WBBSE 10th Class Science Solutions Science & Environment Chapter 3 Heredity and Some Common Genetic Diseases

09/05/2023 Ajit kumar 109 Views 0 Comments

West Bengal Board 10th Class Science Solutions Science & Environment Chapter 3 Heredity and Some Common Genetic Diseases

WBBSE 10th Class Life Science & Environment Solutions

TOPIC – 1

HEREDITY

SUB-TOPIC – 1.1

EREDITY AND VARIATION-EXPLANATION OF SOME IMPORTANT TERMS RELATED TO HEREDITY

SUMMARY

The inheritance of characters from one to next generation by reproduction is called heredity. The scientific explanation of heredity was first given by Mendel and due to this he is known as ‘Father of genetics!
Chromosomes contain genes in linear sequence. Sudden heritable change of chromosome is called mutation.
The difference between different individuals resulting from reproduction is called variation. Example-Normal and roller tongue of human.
Mendel introduced some important terms. For example, ‘allele’ which refers to two alternative forms of a gene. The location of allele in chromosome is called locus. One allele controls one character. When same allele is present twice then the organism is homozygous and when two different alleles are present, the organism is heterozygous. The arrangement of alleles is called genotype and external expression of a character is called phenotype.

Long Answer Type Questions

1. What are variations? Mention some phenotypically distinct human variations.

Ans. Variations

During sexual reproduction and due to mutation, certain external and internal changes occur in some members of a population. These changes among the organisms are known as variations.

Examples of variations in human population

Free and attached earlobe: In human population the soft lower portion of pinna occur in two different forms. One type of pinna has the lobe attached to the side of the face and another type has free hanging lobe. It is found that a pair of dominant alleles controls the formation of free lobe of human pinna. On the other hand, a mutated recessive gene pair is responsible for the formation of pinna with attached lobe. This is an example of phenotypic variation seen in human population, caused by mutated gene.
Roller and normal tongue: 65-81% of the human population are able to roll their tongue but the rest cannot do so. The ability of tongue rolling is a genetic trait, controlled by a pair of dominant alleles. A recessive mutated gene pair, on the other hand, makes one unable to roll the tongue. This is another example of human variation, caused by a recessive mutated gene.

Short Answer Type Questions

1. What is heredity?

Ans. The process of transmission of characters from parents to offspring is known as heredity. Due to heredity, progeny of an organism of any species acquires the features similar to its parents. For example-a mango tree grows from a mango seed or a calf is born from a cow as a result of heredity.

2. Who is known as the ‘Father of genetics’? Why is he regarded as the ‘Father of genetics’?

Ans. Father of genetics: Gregor Johann Mendel is known as the ‘Father of genetics.

Reason: Based on his seven year long (1856 to 1863) experiments, Mendel formulated the laws of heredity. That is why Mendel is regarded as the ‘Father of genetics!

3. What is a monohybrid cross?

Ans. A cross between two organisms carrying two opposite traits of a single character, is called monohybrid cross. A cross between tall and dwarf pea plants or between black and white guinea pig are examples of monohybrid cross.

4. What is a dihybrid cross?

Ans. A cross between two organisms carrying contrasting traits of two different pairs of character, is called dihybrid cross. A cross between a pea plant with yellow cotyledon and round seed and another one with green cotyledon and wrinkled seed or a cross between black and rough furred guinea pig and a white and smooth furred guinea pig are examples of dihybrid cross.

5. What is a dominant trait? Give example.

Ans. Dominant trait: In a cross between two pure and opposite trait-bearing organisms, only one of the traits is expressed in the first filial (F₁) generation. This trait is called as the dominant trait of that organism.

Example: If a cross is performed between pure violet and white flower-bearing pea plants, the F₁ progeny will grow violet flowers only. Here violet flower colour is a dominant trait of that flower.

6. What is recessive trait? Give example.

Ans. Recessive trait: In a cross between two pure and opposite trait-bearing organisms, one of the traits remains dormant in the first filial (F₁) generation. This trait is treated as the recessive trait of that organism.

Example: If a cross is performed between a pure black and a pure white guinea pig, all F₁ offsprings appear black. The white coat colour does not appear in F₁ generation. Here white coat colour is a recessive trait of that guinea pig.

7. Define homozygous organism.

Ans. An organism, having identical alleles in the same locus of both of the homologous chromosomes, is called homozygous for that specific trait. Example-Identical alleles are seen in case of pure tall (TT) or pure dwarf (tt) pea plants, therefore these are homozygous organisms.

8. Define heterozygous organism.

Ans. An organism, having contrasting alleles in the same locus of two homologous chromosomes, is called heterozygous for that specific trait. Example–Contrasting alleles are seen in case of hybrid tall (Tt) pea plants, therefore, these are heterozygous organisms.

9. What is an allele or allelomorph?

Ans. Each of the two alternative forms of a gene, located at the same loci of two homologous chromosomes, controlling two alternative expressions (traits) of the same character, is called an allele or allelomorph. Example-The genes ‘T’ and ‘t’ for tallness and dwarfness respectively examples of alleles.

10. What is phenotype? Give examples.

Ans. Phenotype: Phenotype is the observable physical expression of an organism that results from its genetic makeup.

Examples: Tall and dwarf features are the two phenotypes of pea plant.

11. What is genotype? Give examples.

Ans. Genotype: Genotype is the genetic constitution that controls the expression of all the traits of an organism.

Examples: In pure tall and pure dwarf pea plants, ‘TT’ and ‘tt’ are the respective genotypes. In a hybrid tall pea plant, the genotype is ‘Tt.

12. What is hybridisation?

Ans. Hybridisation is the process of cross breeding between contrasting varieties of a same species with reference to a single or more traits. The cross between a pure tall and a pure dwarf pea plant is a common example of plant hybridisation.

13. What is meant by parental generation?

Ans. Parental generation or P-generation indicates either only two individuals or two groups of organisms, between which the cross is done at the start of any hybridisation experiment. In Mendelian monohybrid cross, pure tall (TT) and pure dwarf (tt) pea plants are regarded as parental generation.

14. Define first filial or F₁ generation.

Ans. The set of progeny resulting from a cross between members of parental generation is called the first filial or F₁ generation. In a cross between pure violet (VV) and pure white (vv) flower-bearing parental generation of pea plants, hybrid violet (Vv) flower-bearing pea plants are produced. The hybrids belong to the first filial or F₁ generation.

15. What is a character in an organism?

Ans. In genetics, the term character is used to define a heritable feature. A character can have two or more variants, which are known as traits. Height of pea plant is a character and each variant of height, such as, tall and dwarf, is a trait.

16. What is trait?

Ans. Trait is a genetically determined characteristic feature of an organism. Generally, each character has two contrasting traits, like height of pea plant has two opposite traits, tall and dwarf.

17. What is meant by pure organism in heredity?

Ans. Any organism, which maintains identical phe notypic and genotypic constitution for successive generations, is called a pure organism. If not crossed with a tall (TT) variety, the dwarf (tt) pea plant remains as it is for generations.

18. What is meant by hybrid organism in heredity?

Ans. The progeny, produced from a cross between two parents with contrasting traits for one or more characters, is called a hybrid organism. In a cross between a pure black (BB) and a pure white (bb) guinea pig, offsprings are born as hybrid with black (Bb) coat.

19. What are haploid and diploid set?

Ans. Haploid set: It refers to the single set of chromosomes, found in reproductive cells or gametes. It is represented as n or N.

Diploid set: It refers to the two sets of chromosomes found in somatic cells (cells canstituting the body). It is represented as 2n or 2N.

Very Short Answer Type Questions

Multiple Choice Questions & Answers [MCQ]

1. Mendelian heredity is seen in case of-

A. Rolling and normal tongue

B. Free and attached earlobe

C. Brown and blue iris

D. All of these

Ans. D

2. The allele, responsible for attached earlobe, is-

A. Dominant

B. Co-dominant

C. Recessive

D. Incompletely dominant

Ans. C

3. Which is the main genetic material of an organism?

A. DNA

B. RNA

C. Both DNA and RNA

D. Either DNA or RNA

Ans. A

4. Who coined the term ‘gene’?

A. Mendel

B. Johannsen

C. Bateson

D. Morgan

Ans. B

5. Who is also known as the ‘Father of heredity’?

A. Morgan

B. Bateson

C. Johannsen

D. Mendel

Ans. D

6. Transmission of parental characters to the next generation is known as-

A. Evolution

B. Heredity

C. Adaptation

D. Genome

Ans. B

7. The sum total of genes of all organisms of a specific population is known as-

A. Gene pool

B. Genome

C. Genetic code

D. Heterozygote

Ans. A

8. The genes, located on the same loci of the homologous chromosomes, responsible for determining the opposite traits of the same character are called-

A. Alleles

B. Polygenes

C. Autosomes

D. Allosomes

Ans. A

9. Who coined the term ‘genetics’?

A. Johannsen

B. Khorana

C. Bateson

D. Darwin

Ans. C

10. Mendel belongs to which country?

A. Australia

B. England

C. Sweden

D. Austria

Ans. D

11. What is the unit of heredity?

A. Chromosome

B. Gene

C. DNA

D. RNA

Ans. B

12. Who proposed the term ‘gene’ for Mendel’s factor?

A. Mendel

B. Johannsen

C. Bateson

D. Morgan

Ans. B

13. Permanent heritable change of gene is called –

A. Allele

B. Mutation

C. Evolution

D. Adaptation

Ans. B

14. Who introduced the concept of mutation?

A. Mendel

B. Darwin

C. Morgan

D. de Vries

Ans. D

15. Roller tongue is ……….. type of character.

A. Recessive

B. Dominant

C. Incompletely dominant

D. None of the above

Ans. B

16. The external expression of a character is called-

A. Genotype

B. Phenotype

C. Allele

D. Gene

Ans. B

17. Aa x aa is an example of-

A. Monohybrid cross

B. Dihybrid Cross

C. Test Cross

D. None of the above

Ans. C

Answer in a single word or sentence

1. What is genetics?

Ans. The branch of biological science that deals with the gene and heredity, is known as genetics.

2. What is the structural and functional unit of heredity?

Ans. Gene is the structural and functional unit of heredity.

3. Where are genes located?

Ans. Genes are located on chromosomes.

4. What is it called, when sexual reproduction and random mutation lead to phenotypic and genotypic differences among individuals?

Ans. When sexual reproduction and random mutation lead to phenotypic and genotypic differences among individuals, it is termed as variation.

5. What is Mendelism?

Ans. The findings of Mendel on inheritance of characters from parents to offspring and Mendel’s laws of heredity, which were derived from these observations, are collectively known as Mendelism.

6. Which term is used in genetics to denote the observable features of any organism?

Ans. Phenotype

7. What is gene?

Ans. Gene is a particular segment of DNA that controls the expression of a specific biological character in an organism.

8. Which term denotes the transfer of parental features to the offspring?

Ans. Heredity

9. Which character is expressed in F₁ generation of Mendelian monohybrid cross?

Ans. A dominant character is expressed in F_₁ generation of Mendelian monohybrid cross.

10. Which character is not expressed in F_₁ generation of Mendelian monohybrid cross?

Ans. A recessive character is not expressed in F_₁ generation of Mendelian monohybrid cross.

11. Name the cross between two opposite traits of a single character.

Ans. The cross between two opposite traits of a single character is called monohybrid cross.

12. Name the type of offsprings that inherits identical alleles of a character from parents.

Ans. An offspring that inherits two identical alleles of a specific character from parents, is called homozygous offspring.

13. Name the type of offspring that inherits two dissimilar alleles of a character from parents.

Ans. An offspring that inherits two dissimilar alleles of a specific character from parents, is called heterozygous or hybrid offspring.

14. Which ratio represents the genetic constitution of the progeny of a hybrid cross?

Ans. Genotypic ratio

15. What is locus?

Ans. The region of chromosome where a gene is located is called locus.

16. Give an example of variation inherited in man along the generation.

Ans. Hair colour

Fill in the blanks

1. A zygote having two identical alleles is called ……….

Ans. Homozygote

2. A ………… is formed, by the union of two gametes carrying contrasting alleles.

Ans. Heterozygote

3. ………… is the unit of heredity.

Ans. Gene

4. The parental character, which is not expressed in F_₁ generation of monohybrid cross, is called ……… character.

Ans. Recessive

5. The specific location of a gene on a chromosome is called ……….. of the gene.

Ans. Locus

6. Free lobed ear is formed by a pair of …………. genes.

Ans. Dominant

7. Mutation generates ………….

Ans. Variation

8. Generally, the number of ……….. within the cells of an organism is constant.

Ans. Chromosomes

9. Human genome contains about ……….. different genes.

Ans. 25000

10. Roller tongue producing gene is a ………… type of gene.

Ans. Autosomal dominant

11. Different forms of a gene is called ………….

Ans. Allele

12. In heterozygous organism ………. character is expressed.

Ans. Dominant

13. The individual in which there are two different alleles of a gene is called ………

Ans. Hetrozygote

14. Individual containing Bb genotype is ……….. type of individual.

Ans. Heterozygous

State true or false

1. Mendel is the ‘Father of genetics.

Ans. True

2. The branch of science, that deals with gene and heredity, is known as genetics.

Ans. True

3. Two opposite variations of a gene are known as alleles.

Ans. True

4. Mendel denoted the unit of heredity as ‘gene’.

Ans. False

5. RNA is the universal genetic material.

Ans. False

6. In Mendelian experiment, ‘TT’ indicates pure tall character of the pea plant.

Ans. True

7. Sudden heritable permanent change of chromosome or gene is called variation.

Ans. False

8. T and t allele together form a homozygote.

Ans. False

9. The external expression of a character is called phenotype.

Ans. True

SUB-TOPIC – 1.2

MENDEL’S WORK ON PEA PLANT; MENDEL’S LAWS AND THEIR DEVIATION

SUMMARY

Mendel performed experiments on pea plants to study inheritence pattern. He chose seven characters of pea plants like stem height, seed colour and shape, pod colour and shape, flower colour and position. Each character has a dominant and a recessive phenotype. He performed monohybrid cross with single character and dihybrid cross with two characters.
Mendel derived his first law i.e. law of segregation from the monohybrid cross. This law states that characters never get mixed rather get segregated in the second generation, Mendel’s second law ie. law of independent assortment came from the dihybrid cross. This law states that characters not only segregate rather are expressed in all possible combination.
Deviation from Mendel’s principle is exhibited by certain organisms in terms of certain characters. The inheritance of flower colour of Mirabilis jalapa (4 o’clock plant) one such example where the F₁ hybrid organism shows intermediate phenotype of two parents is and none of the parental phenotype is completely dominant over other.

Long Answer Type Questions

1. Explain the two conclusions of Mendel’s monohybrid cross. Rough coat (RR) is dominant and smooth coat (rr) is recessive character for guinea pigs. If two heterozygous rough coated guinea pigs are crossed, what will be the types of offsprings in F_₁, generation?

Ans. Two conclusions of Mendel’s monohybrid cross

Analysing the results of monohybrid cross of garden pea plants, Mendel reached two conclusions. These are popularly known as the law of dominance and the law of segregation.

Law of dominance: In a cross between two parents that are pure for contrasting traits only one of the two expresses itself in the first filial generation. This is controlled by a dominant factor that helps to express the dominant trait by suppressing the recessive one. Here, the expressed one is the dominant trait and the suppressed one is the recessive trait.
Law of segregation: This law states that during formation of gametes, two alleles controlling each character, move apart due to separation of the homologous chromosomes during meiosis. Thus, each gamete receives only one allele of each character on random basis.

Monohybrid cross between heterozygous rough coated guinea pigs

Let us mark rough coat (dominant) as ‘RR’ and smooth coat (recessive) as ‘rr!

Therefore, the genotype of a heterozygous rough coated guinea pig should be denoted as ‘Rr. The cross between two heterozygous rough coated Rr guinea pigs is schematically represented here.

From this cross, we get two different phenotypes, 75% or 3/4th part of the progeny are rough coated and remaining 25% or 1/4th part are smooth coated. Therefore, the phenotypic ratio is- Rough coat: Smooth coat 3:1. The genotypic ratio of this cross is- Pure rough coat: Hybrid rough coat: Pure smooth coat = 1:2:1.

2. In a cross between two pea plants bearing, pure violet [dominant] and pure white [recessive] flowers, what will be the ratio of pure violet and pure white flowered plants in the F_₂ generation?

Ans. Ratio of pure violet and pure white flowered plants in F_₂ generation

Let us represent the dominant pure violet flower character as (VV) and the recessive pure white flower character as (vv).

In a cross between the pure violet (VV) and pure white (vv) flowered pea plants, all F_₁ progeny grow violet flowers. This is due to the dominant nature of the violet flower colour. If selfpollination is allowed in the F_₁ plants, two different phenotypes will appear in the F₂ generation. Among the F₂ progeny, 3/4th parts of plants grow violet flower and remaining 1/4th part of plants bear white flowers. Of these 3/4th parts of plants bearning violet flower, 1/4th part F, generation of plants grow pure violet and 2/4th parts of plants grow hybrid violet flowers. Therefore, among the F₂ progeny, 1/4th part of plants (25%) grow pure violet, 2/4th parts of plants (50%) grow hybrid violet and remaining 1/4th part of plants (25%) grow pure white flowers.

The cross is schematically represented here with checker board.

Therefore, the ratio of violet and white flowered pea plants (phenotypic ratio) is 3: 1. The ratio of pure violet, hybrid violet and pure white flowered pea plants of the F₂ generation (genotypic ratio) is 1: 2: 1. The ratio of pure violet and pure white flowered plants of the F₂ generation is 1 : 1.

3. Explain with checker board, how Mendel reached the conclusion to his monohybrid cross experiment.

Ans. The conclusion of Mendel’s monohybrid cross

Garden pea plants have seven different genetic characters, each having two distinct opposite traits. For monohybrid cross experiment, Mendel selected only one character, that is the height of the garden pea plant. The two opposite traits are denoted as ‘TT’ for pure tall and ‘tt’ for pure dwarf. The steps of the experiment are mentioned here.

The first filial generation: Mendel collected pollens from a flower of a pure tall pea plant and placed it on the stigma of some emasculated flowers (flowers, artificially converted into unisexual female flower by removing the anthers) of dwarf pea plants. The progeny plants produced from this cross were the first filial or F_₁ generation, all of which were tall in phenotype.
The second filial generation: Mendel then allowed self pollination among the F_₁ plants and got the F₂ progeny with two different phenotypes. 75% of these were tall and 25% were dwarf = 3:1. Among the F_₂ plants, 25% were pure tall, 50% were hybrid tall and 25% were pure dwarf. Therefore, the genotypic ratio of monohybrid cross is Pure tall: Hybrid tall: Pure dwarf = 1:2:1.
The cross is schematically represented here with checker board

Conclusion: The experimental result shows that during hybridisation the parental factors, which come together in F_₁ generation, do not get mixed. During gamete formation of F_₁ generation, the factors segregate from each other and each gamete carries one factor. Thus, by analysing the result of monohybrid cross, Mendel framed the law of segregation.

4. Explain the monohybrid cross of an animal and draw a conclusion from this experiment.

Ans. Monohybrid cross of an animal and its conclusion

Monohybrid cross can be performed on guinea pig. Black coat (BB) of guinea pig is a dominant trait over white coat (bb). In a cross between pure black and white coated guinea pigs, all F_₁ offsprings are black (Bb). These hybrid black F_₁ guinea pigs give birth to F₂ offsprings with two different phenotypes, black and white. Out of this 75% is black and 25% is white. Therefore the phenotypic ratio is 3:1. Among F_₂ offsprings, three different genotypes are found. These are pure black (BB), hybrid black (Bb) and pure white (bb) in the ratio of 1:2:1.

The monohybrid cross of guinea pig is schematically represented here.

Conclusion: The result of the monohybrid cross in between black and white guinea pigs maintains absolute similarity with the Mendelian monohybrid cross and supports the law of segregation.

5. Describe Mendel’s dihybrid cross experiment and explain the conclusion drawn from it.

Ans. Dihybrid cross experiment

For his dihybrid cross experiment, Mendel selected two different characters of garden pea plant, each having two distinct contrasting traits. The characters are-[1] Colour of seed or cotyledon and [2] Shape of seed. For colour of seed, the contrasting traits are yellow (YY) and green (yy), where yellow one is dominant over green. For shape of seed, the opposite traits are round (RR) and wrinkled (rr), where round is dominant over wrinkled.

First filial generation: Mendel crossed pure round and yellow seed bearing pea plants (RRYY) with wrinkled and green seed bearing pea plants (rryy). From this cross he got the F₁ hybrids with yellow cotyledons and round seeds (YyRr).
Second filial generation: Mendel allowed self pollination among the F₁ plants and F₂ offsprings were produced. These were of four different phenotypes-round yellow, wrinkled yellow, round green, and wrinkled green in the ratio of 9:3:3:1. By analysing the genotypes of these F₂ plants, Mendel found nine different combinations in the ratio of 1:2:2:4:1:2:1:2:1.

Mendel’s dihybrid cross experiment is schematically represented here.

Checker board of F₂ generation

Phenotype and genotype of F_₂ generation of Mendelian dihybrid cross

Phenotype	Phenotypic ratio	Genotype	Genotypic ratio
Round yellow	9	RRYY RrYY RRYy RrYy	1 2 2 4
Wrinkled yellow	3	rrYY rrYy	1 2
Round green	3	RRyy Rryy	1 2
Wrinkled green	1	rryy	1

Conclusion: From the results of this experiment, Mendel came to the following conclusions. [1] The factors, responsible for any of the cotyledon colours and shapes of the seeds, do not get mixed in the F₁ progeny. All four factors segregated during gamete formation of the F₁ plants. [2] The gametes, which carry the colour and shape regulating factors of pea seeds in segregated manner, unite independently in all possible combinations to form the F2 progeny. Based on these conclusions, Mendel framed his second law of heredity or the law of independent assortment.

6. Mention the seven pairs of contrasting characters of garden pea plant as selected by Mendel.

Ans. Seven pairs of contrasting characters of garden pea plant

For his experiment on heredity, Mendel selected seven pairs of opposite characters of garden pea plant, which are mentioned below in a table.

Characters	Dominant	Recessive
1. Height of the plant	Tall	Dwarf
2. Position of flower	Axial	Terminal
3. Shape of pod	Inflated	Constricted
4. Colour of pod	Green	Yellow
5. Colour of flower	Violet	White
6. Shape of seed	Round	Wrinkled
7. Colour of seed or cotyledon	Yellow	Green

7. Mention the causes of Mendel’s success in his experiments on heredity with garden pea Which types of gametes unite to form a male baby?

Ans. Causes of Mendel’s success in his experiments on heredity with garden pea plants

[1] Mendel selected the pure breed of pea plants for a particular character after two years of continuous successive self-breeding. [2] The seven pairs of factors (genes), responsible for the selected contrasting traits, are present on seven separate sets of homologous chromosomes. This feature helps in the independent assortment of the factors. [3] Pea plants are easy to breed, the life cycle is short and therefore, Mendel could study several generations in a short time. Pea flowers are bisexual, naturally self-pollinating, but Mendel successfully manipulated it for artificial crosspollination. He was also successful in preventing any undesired pollination. [4] Mendel, though selected seven traits of the pea plant, but worked on one or two at a time. This helped him in collection and analysis of the data. [5] The characters, selected by Mendel, were sharply contrasting and showed complete dominance. [6] Mendel used many samples at a time for breeding to get a large number of progeny, which helped him for statistical analysis of the data and to get the correct ratio between two or more contrasting characters.

Gametes required to produce a male baby

Union of an ovum with 22 autosomes and an X chromosome (22A+X) and a sperm with 22 autosomes and a Y chromosome (22A+Y) can produce a male baby with genotype (44A+XY).

8. What is hybrid organism? What will be the phenotype of the F₁ offspring from a cross between a hybrid black and a pure white guinea pig. Explain your answer.

Ans. Hybrid organism

The progeny, produced from a cross between parents bearing two contrasting traits with respect to a single or more characters, is called hybrid organism.

Hybridisation experiment on guinea pig

In a cross between hybrid black (Bb) and pure white (bb) guinea pigs, two different phenotypes will be seen among the F_₁ offsprings. 50% of the offsprings will have black coat and remaining 50% will be white coated. Therefore, the phenotypic ratio will be Black White = 1:1. The cross is schematically represented here.

Explanation: The genotype of the hybrid black guinea pig is ‘Bb. Therefore, this parent produces two different types of gametes, ‘B’ and ‘b. The other parent, pure white guinea pig is homozygous recessive having a genotype of ‘bb. This parent produces only ‘b’ type of gametes. Union of ‘B’ and ‘b’ gametes produce hybrid black ‘Bb’ offsprings. On the other hand, the fertilisation between two ‘b’ gametes from two parents gives rise to pure white ‘bb’ offspring. The checker board of the F_₁ generation of this cross clearly shows that the proportion of hybrid black and pure white offsprings is equal.

9. The black coat of guinea pig is dominant over the white coat. If a cross is performed between two hybrid black guinea pigs, what will be the result in the F_₁ generation? Which types of gametes unite to form a female baby?

Ans. Crossing of hybrid black guinea pig

Let the allele for dominant black coat colour be ‘B’ and the recessive white coat colour be ‘b’ So, the genotype of a hybrid guinea pig can be denoted as ‘Bb.

A hybrid black coated guinea pig may produce two different types of gametes ‘B’ and ‘b. Therefore, the F_₁ progeny produced from a cross between two hybrid black guinea pigs will have two different phenotypes. 75% of them will be black and remaining 25% will be white. Hence, the phenotypic ratio for Black : white is 3:1. If the genotypes of F, progeny are analysed on a checker board, we will see three different type- 25% of it is pure black, 50% is hybrid black and remaining 25% is pure white. Therefore ratio for pure black: hybrid black: pure white is 1:2:1.

The cross and the checker board is shown here.

Gametes required to produce a female baby

Union of an ovum with 22 autosomes and an X chromosome (22A+X) and a sperm with 22 autosomes and an X chromosome (22A+X) can produce a female baby with genotype 44A+XX.

10. Describe a dihybrid cross experiment on animal (guinea pig) and analyse the result.

Ans. Dihybrid cross experiment on animal

In the dihybrid cross experiment on guinea pig, the coat colour and fur character are considered. The two opposite traits for coat colour are black and white. The opposite traits for fur character are rough and smooth. The black coat (BB) and rough fur (RR) are dominant over white coat (bb) and smooth fur (rr) respectively.

First filial generation: A cross is done between a black and rough furred male and a white and smooth furred female guinea pigs to get the F_₁ offsprings. Eventually, all these hybrid offsprings are with black coat and rough fur (BbRr).
Second filial generation: The F, offsprings are allowed to breed among themselves. They four different types of phenotypes. 9 animals of which are black-rough furred, 3 animals black-smooth furred, 3 animals are white-rough furred and remaining 1 animal is white-furred. Therefore, the phenotypic ratio of this dihybrid cross is 9:3:3:1. The F_₁ hybrids four different types of gametes- BR, Br, bR and br. These four different varieties of male female gametes unite with each other in all possible combinations to produce F₂ with nine different types of genotypes in the ratio of 1:2:2:4:1:2:1:2:1.
The checker board for the above mentioned cross is represented here.

Checker board of F₂ generation

Phenotype and genotype of F₂ generation of Mendelian dihybrid cross

Phenotype	Phenotypic ratio	Genotype	Genotype ratio
Black, rough fur	9	BBRR BBRr BbRR BbRr	1 2 3 4
Black, smooth fur	3	BBrr Bbrr	1 2
White, rough fur	3	bbRR bbRr	1 2
White, smooth fur	1	bbrr	1

Conclusion: The result obtained from this experiment on dihybrid cross of guinea pig is the same as that of the Mendelian dihybrid cross of garden pea plants. This experimental result confirms that the law of independent assortment is also applicable to the heredity of the animals like guinea pig.

11. Why did Mendel select garden pea plants for his experiments on heredity?

Or, Mention the main causes of selection of pea plants (Pisum sativum) by Mendel for his experiments on heredity.

Ans. Causes of selection of pea plants by Mendel

[1] Pea flower is naturally self-pollinating. The stamens and pistil always remain closed inside the petals, therefore, cross-pollination by insects and air do not occur. However, these flowers can be manipulated for artificial cross-pollination for experimental purpose. [2] The bisexual pea flowers can be emasculated and transformed into female flowers by simply cutting the stamens and removing the anthers. [3] Pea plants have distinct contrasting phenotypic features and the characters remain unchanged for generations. [4] The life cycle of pea plants is short, hence, a number of generations can be studied within a few years. The dormancy of seed is brief, therefore, a new generation can grow quickly. [5] The hybrids of pea plants are fertile and these are suitable for both selfing and crossing to produce next generations. [6] Each pea plant produces several seeds, therefore, analysis of the result can be done more accurately.

12. Describe the experimental works of Mendel on garden pea plants.

Ans. Mendel’s work on garden pea plant

[1] Mendel first visually selected seven distinct contrasting characters of the pea plant. [2] To become sure of homozygosity of the parental generation, he allowed selfing of selected characterbearing plants for several successive generations. [3] Before crossing, Mendel gently opened the petal cover to expose the stamens and cut the anthers before they mature. By this process, he emasculated the bisexual flowers to prevent undesired self-pollination. [4] For crossing, Mendel collected pollens from a selected flower from a parental plant with fine brush and placed it delicately on the stigma of the emasculated flowers of the other parental plant, bearing the opposite trait. He performed reciprocal crossing between two parental pea plants. [5] After crossing, he covered the cross-pollinated flower with fine muslin cloth to prevent any undesired pollination. [6] He collected seeds from the resultant fruits of the cross and sowed them to get the next generation. [7] Mendel meticulously studied the concerned characters of each generation and statistically analysed the result to reach a conclusion.

By this process, Mendel performed separate experiments on different sets of contrasting traits before framing his famous laws of heredity.

13. What is incomplete dominance? Explain with suitable example.

Ans. Incomplete dominance

In a cross between two pure contrasting trait-bearing parents, sometimes none of the traits dominates completely over the other so the phenotypic expressions of both the parents’ characters are subdued partially in the F, generation. This event is treated as incomplete dominance.

Explanation of incomplete dominance

Among plants, incomplete dominance is clearly noticed in four o’ clock (Mirabilis jalapa) plants. In this plant, two contrasting flower colours are red and white. Let us mark the pure red flower as ‘RR’ and pure white as ‘rr’. When these two contrasting flower-bearing plants are crossed, the F_₁ generation grows neither red nor white flowers, instead they grow pink flowers. Here, phenotypic expressions of flower colour of both the parents are subdued to some extent. When these F_₁ plants are self pollinated, three different phenotypes are produced. These are – 25% red, 50% pink and 25% white. The genotypes of red, pink and white flower-bearing genotypic plants are-‘RR, ‘Rr’ and ‘rr’. Here, both phenotypic and genotypic ratios are identical, i.e., 1: 2: 1, which is a deviation from Mendelian monohybrid cross.

Short Answer Type Questions

1. Mention the Mendelian laws of heredity.

Ans. Mendel proposed two laws of heredity, they are-[1] Law of segregation and [2] Law of independent assortment.

2. How did Mendel explain the occurrence of all tall pea plants in the F₁ generation of his monohybrid cross experiment?

Ans. In the monohybrid cross between pure tall and pure dwarf pea plants, all progeny of the F₁ generation came out as tall. From this observation, Mendel concluded that the tall character is a dominant one, which was expressed by suppression of the recessive dwarf character. From this finding, Mendel framed a law of heredity, known as the law of dominance.

3. Which type of offspring will come out of a monohybrid cross between a pure black and a pure white guinea pig? Why does it happen?

Ans. In a cross between a pure black and a pure white guinea pig, all F₁ offsprings will be hybrid black.

In guinea pig, the black coat colour is dominant over the white coat colour. Therefore, the gene for black coat colour will express itself by suppressing the gene for white cote colour.

4. Which law of heredity did Mendel frame from the results of his famous monohybrid cross experiment? State the law.

Ans. Law of heredity from monohybrid cross: From the results of the monohybrid cross experiment on garden pea plants, Mendel framed the law of segregation.

Law of segregation: During hybridisation, the factors of each character are transmitted to the F₁ generation from their parents but do not get mixed. During gamete formation, these factors segregate from each other, so that each gamete receives only one factor for each character.

5. What is a test cross?

Ans. To determine the genotype of an individual exhibiting the dominant phenotype of a trait, it is crossed with an individual that is homozygous recessive for that trait. This cross is known as the test cross. Example-To test the genotype of the tall F₁ pea plants in Mendel’s monohybrid cross, these can be crossed with homozygous recessive dwarf (tt) pea plants.

6. What is a back cross?

Ans. A cross between any of the parents or any individual with genotype, identical to any of the parents, and a member of F₁ generation of any individual with similar genotype to that of the F₁ progeny is known as the back cross. Example-A cross between ‘TT’ and ‘Tt’ and ‘tt’ and ‘Tt’ are the examples of back crosses with respect to Mendel’s monohybrid cross.

7. Explain: ‘Every test cross is a back cross’.

Ans. A cross between any of the parents ‘TT’ or ‘tt’ and a member of the F₁ generation “Tt’ is a back cross. In Mendelian monohybrid cross, one of the parents is homozygous recessive (tt). When this recessive homozygous (tt) parent is used for back cross with a F₁ progeny (Tt), it becomes a test cross. Therefore, every test cross may be treated as a back cross.

8. What is incomplete dominance?

Ans. Incomplete dominance is a genetic event where one of the alleles does not dominate completely over the other, but both the alleles express themselves partially when both are present together in the hybrid.

9. What is a checker board? Why is it known as the Punnett square?

Ans. Checker board: The tabular representation of a genetic cross showing all genotypes of offsprings, produced from every possible combination of gametes, is known as checker board.

Punnett Square: Geneticist Reginald C Punnett, first represented a cross in tabular form. Therefore, checker board is also known as the Punnett square, after his name.

10. Give example of incomplete dominance in a plant and an animal.

Ans. Example of incomplete dominance in a plant: From a cross between red and white flowered four o’ clock (Mirabilis jalapa) plants, we get pink flower in F_₁ generation.

Example of incomplete dominance in an animal: If pure black Andalusian hen is crossed with a pure white cock, the F_₁ chicks will be blue in colour.

11. Mention the constrasting traits of any two characters of garden pea plant.

Ans. Two characters of garden pea plant are height and flower colour. Opposite traits of height are tall and dwarf. Opposite traits of flower colour are violet and white.

12. What will be the phenotypes of the two pea plants, when their genotypes are ‘TT’ and ‘tt’? Mention the chromosomal distribution of normal human male and female.

Ans. Phenotypes of ‘TT’ and ‘tt’: Phenotype of ‘TT’ will be tall and ‘tt’ will be dwarf.

Chromosomal distribution of human: Chromosomal distribution of normal human male is 44A+XY and that of female is 44A+XX..

13. The genotype of a sweet pea plant bearing round and yellow seeds is ‘RrYy’. Which types of gametes may be produced from this plant?

Ans. From a pea plant with genotype ‘RrYy, four different types of gametes may be produced. These are ‘RY, ‘Ry’, ‘rY’ and ‘ry!

14. In a dihybrid cross experiment, black and rough coated male is crossed with a white and smooth coated female guinea pig. What will be the phenotypes of the F₂ progeny?

Ans. In a cross between a black and rough coated male with a white and smooth coated female guinea pig, the F2 progeny will be of four types. These are-[1] Black and rough coated, [2] Black and smooth coated, [3] White and rough coated and [4] White and smooth coated.

15. What is genome?

Ans. All the genes present in the haploid set of chromosomes of an individual organism are collectively known as genome. The genome is carried through the chromosomes of a gamete from an individual parent to its offspring.

16. How did Mendel explain the combinations of different dominant and recessive factors in F_₂ generation of a dihybrid cross?

Ans. In a dihybrid cross, all different types of gametes, carrying various combinations of dominant and recessive factors, unite randomly in all possible combinations to create the F₂ offsprings. During this process, no factor affects the expression of any other. Mendel explained this random distribution of factors as independent assortment.

17. What are the limitations of law of segregation?

Ans. [1] When one character is controlled by more than one gene then in that case, segregation may take place in different ratio other than monohybrid cross. [2] In case of incomplete dominance segregation takes place but not in a ratio of monohybrid cross.

18. What is checker board?

Ans. Checker board is a method of expressing different combinations of genotypes through a tabular representation of the genetic cross. It was discovered by Reginald punnet.

19. ‘Dwarf plants are always pure’-Justify it.

Ans. Dwarf phenotype is a recessive phenotype. In presence of dominant allele, the recessive one is not expressed. Therefore recessive character is always expressed in homozygous. So dwarf plants are always homozygous or pure.

Very Short Answer Type Questions

Multiple Choice Questions & Answers [MCQ]

1. The laws of heredity were framed by-

A. Hugo de Vries

B. Darwin

C. Lamarck

D. Mendel

Ans. D

2. Mendelian concept deviates in-

A. Law of segregation

B. Law of dominance

C. Law of incomplete dominance

D. Law of independent assortment

Ans. C

3. A genetic cross between hybrid offspring and one of the homozygous parental types, is known as –

A. Back cross

B. Test cross

C. Reciprocal cross

D. Final cross

Ans. A

4. In a cross between red (WW) and white (ww) flower bearing evening primrose plants, all plants of F₁ generation bear pink (Ww) flowers. It is an example of-

A. Hybridisation

B. Dominance

C. Incomplete dominance

D. Mutation

Ans. C

5. A cross is performed between white (recessive) and violet (dominant) flower bearing garden pea plants. What would be the percentage of white flower bearing plants F₂ generation?

A. 100%

B. 25%

C. 50%

D. 75%

Ans. B

6. What would be the genotypic ratio of the offsprings from a test cross of an organism having AaBb genotype?

A. 1:1:1:1

B. 1:2:1

C. 3:1.

D.. 9:3:3:1

Ans. A

7. The findings of Mendel on heredity and the laws of inheritance are collectively known as-

A. Mendelism

B. Monohybrid cross

C. Genetics

D. Dihybrid cross

Ans. A

8. The genotype of a pure dwarf pea plant is-

A. TT

B. Tt

C. tt

D. Ttt

Ans. C

9. How many pairs of contrasting traits of pea plant did Mendel select for carrying out his experiments on heredity?

A. One pair

B. Two pairs

C. Seven pairs

D. Nine pairs

Ans. C

10. As per Mendel’s experiment on monohybrid cross, a cross is performed between a heterozygous tall (Tt) and a homozygous dwarf (tt) garden pea plant. What would be the percentage of tall pea plants in the first filial (F_₁) generation?

A. 25%

B. 50%

C. 75%

D. 100%

Ans. D

11. The phenotypic ratio in F₂ generation of Mendel’s monohybrid cross is-

A. 1:2:1

B. 3:1

C. 9:3:3:1

D. 1:1

Ans. B

12. The phenotypic ratio in F₂ generation of Mendel’s dihybrid cross is-

A. 1:2:1

B. 3:1

C. 9:3:3:1

D. 1:1

Ans. C

13. What would be the percentage of dwarf pea plants in F_₁ generation resulting from a cross between two hybrid tall pea plants?

A. 25%

B. 50%

C. 75%

D. 100%

Ans. A

14. Dwarf pea plants are always-

A. Homozygous

B. Heterozygous

C. Hybrid tall

D. Hemizygous

Ans. A

15. Name the Mendelian law that is derived from dihybrid cross.

A. Law of segregation

B. Law of incomplete dominance

C. Law of dominance

D. Law of independent assortment

Ans. D

16. A cross is performed between two hybrid tall pea plants. What would be the percentage of tall and dwarf offsprings respectively, in the F₁ generation of this cross?

A. 50% and 25%

B. 25% and 25%

C. 75% and 25%

D. 50% and 50%

Ans. C

17. The pea plants, produced from the seeds resulting from a cross between hybrid tall (Tt) and pure dwarf (tt) pea plants will be-

A. All tall

B. All dwarf

C. 50% tall and 50% dwarf

D. 75% tall and 25% dwarf

Ans. C

18. The numerical ratio of pure black and pure white offsprings obtained in the F₂ generation of a monohybrid cross between pure black (BB) and pure white (bb) guinea pig, is-

A. 1:1

B. 1:2

C. 2:1

D. 3:1

Ans. A

19. The numerical ratio of pure white and hybrid black offsprings obtained in the F_₂ generation of a monohybrid cross between pure black (BB) and pure white (bb) guinea pig, is-

A. 1:1

B. 1:2

C. 3:1

D. 2:1

Ans. B

20. The ratio of pure genotypes produced in F2 generation of a monohybrid cross is-

A. 1:1

B. 1:2

C. 1:3

D. 3:1

Ans. A

21. The percentage of hybrid tall offsprings obtained from a cross between two hybrid tall pea plants is-

A. 25%

B. 50%

C. 75%

D. 100%

Ans. B

22. The ABO blood group in human is an example of-

A. Dominance

B. Codominance

C. Polygene

D. Incomplete dominance

Ans. B

23. Mendel’s Law of segregation is derived from-

A. Monohybrid cross

B. Dihybrid cross

C. Hybridisation

D. Variation

Ans. A

24. The 1:2:1 ratio in the F₂ generation of Mendel’s monohybrid cross is-

A. Phenotypic

B. Genotypic

C. Homozygotic

D. Heterozygotic

Ans. B

25. Self pollination is possible in garden pea flower, because it is a-

A. Male flower

B. Female flower

C. Unisexual flower

D. Bisexual flower

Ans. D

26. Which of the following indicates test cross of Mendel’s monohybrid experiment?

A. Tt x TT

B. Tt x Tt

C. Tt x tt

D. TT x TT

Ans. C

27. In which of the following cases, both phenotypic and genotypic ratios are 1:2:1 in F_₂ generation of a monohybrid cross?

A. Complete dominance

B. Incomplete dominance

C. Super dominance

D. Mendelian dominance

Ans. B

28. The allelic state or the genetic constitution of an organism is known as-

A. Allelomorph

B. Gene

C. Genotype

D. Phenotype

Ans. C

29. Which of the following is a dominant character?

A. Stem height-Dwarf

B. Shape of seed-Wrinkled

C. Cotyledon colour-Yellow

D. Flower colour-White

Ans. C

Answer in a single word or sentence

1. Write down the scientific name of garden pea plant.

Ans. Pisum sativum

2. What is the phenotypic ratio in F_₂ generation of a monohybrid cross?

Ans. The phenotypic ratio in F, generation of a monohybrid cross is, Dominant:Recessive=31.

3. What is the genotypic ratio in F_₂ generation, of a monohybrid cross?

Ans. The genotypic ratio in F₂ generation of a monohybrid cross is-Pure dominant : Hybrid: Pure recessive = 1:2:1.

4. Give an example of a dominant character of guinea pig.

Ans. Black coat colour is a dominant character of guinea pig.

5. in a monohybrid cross, the phenotypic and genotypic ratio of F₂ generation are 3:1 and 1:2:1 respectively. What does this observation indicate?

Ans. This observation indicates the complete dominance of the concerned character.

6. What does ‘Tt’ indicate in Mendel’s experiment?

Ans. In Mendel’s experiment, ‘Tt’ indicates the genotype of a hybrid tall pea plant.

7. Which type of pea plant is denoted by ‘TT’ in Mendel’s experiment?

Ans. In Mendel’s experiment, ‘TT’ indicates pure tall pea plant.

8. Which type of pea plant is denoted by ‘tt’ in Mendel’s experiment?

Ans. In Mendel’s experiment, ‘tt’ indicates pure dwarf pea plant.

9. Mention a character and its opposite traits found in guinea pig.

Ans. Coat colour is a character of guinea pig, which has two opposite traits-black and white.

10. Which is the dominant colour of flowers of garden pea plant?

Ans. The dominant colour of flowers of garden pea plant is violet.

11. Which ratio indicates the external features of the progeny of a hybrid cross?

Ans. Phenotypic ratio

12. In which journal Mendel’s paper on heredity of garden pea plants was published?

Ans. Mendel’s paper on heredity of garden pea plants was published in the Journal of Natural History Society at Brunn.

13. What does the ratio of 3:1 indicate in genetics?

Ans. The ratio of 3:1 indicates the phenotypic ratio of the F₂ progeny of monohybrid cross.

14. What does the ratio of 1:2:1 indicate in genetics?

Ans. The ratio of 1:2:1 indicates the genotypic ratio of the F_₂ progeny of monohybrid cross.

15. What does the ratio of 9:3:3:1 indicate in genetics?

Ans. The ratio of 9:3:3:1 indicates the phenotypic ratio of the F₂ progeny of dihybrid cross.

16. Which Mendelian law is derived from the result of monohybrid cross experiment?

Ans. The law of segregation is derived from the result of Mendel’s monohybrid cross experiment.

17. Which Mendelian law is derived from the result of dihybrid cross experiment?

Ans. The law of independent assortment is derived from the result of Mendel’s dihybrid cross experiment.

18. Who first designed the checker board?

Ans. Reginald C Punnett, a British geneticist, first designed the checker board.

19. What does Mendelian factors mean?

Ans. Mendelian factors are the alleles of genes, which are responsible for expression of various hereditary characters.

20. What is mulatto?

Ans. The medium complexioned offspring, born to pure black and pure white parents, is called mulatto.

21. In case of guinea pig whether the phenotype of the two genotypes bbRR and bbRr is same?

Ans. Yes, the phenotype of the two genotypes bbRR and bbRr will be same in case of guinea pig.

22. Write the phenotypic ratio obtained in the F_₂ generation of Mendel’s dihybrid cross experiment.

Ans. 9:3:3:1

23. Write the genotypic ratio obtained at 2nd filial generation in the monohybrid experiment done by Mendel.

Ans. 1:2:1

24. Which law Mendel concluded from his dihybrid cross experiment?

Ans. Law of independent assortment.

Fill in the blanks

1. An individual which carries both dominant and recessive alleles is called ………. individual.

Ans. Hybrid

2. Mendel’s first law of heredity is known as the law of ………..

Ans. Segregation

3. Mendel’s second law of heredity is known as the law of …………

Ans. Independent assortment

4. In monohybrid cross between red and white flower bearing evening primrose plants, the phenotypic ratio of the F₂ progeny is ………..

Ans. 1:2:1

5. The parental generation of monohybrid cross is marked as ……….. generation.

Ans. P

6. Mendel performed ………. pollination between the flowers of pure tall and pure dwarf pea plants.

Ans. Cross

7. To get F_₂ generation, Mendel allowed ……….. pollination among F₁ plants.

Ans. Self

8. Yellow colour of cotyledons of pea plants is a ………. character.

Ans. Dominant

9. SER Hybridisation between two traits of a single character is known as ……….. cross.

Ans. Monohybrid

10. Permanent and heritable change in the number and structure of gene or chromosome is known as ……….

Ans. Mutation

11. Mendel selected ……….. number of characters of pea plant for his experiment.

Ans. Seven

12. Different ……….. of an individual may show same phenotype.

Ans. Genotypes

13. White and smooth fur of guinea pig is a …………. character.

Ans. Recessive

14. The ratio of TT:Tt:tt in monohybrid cross is …………

Ans. 1:2:1

SUB-TOPIC – 1.3

SEX DETERMINATION OF HUMAN

SUMMARY

The male contains 44 autosomes and two sex chromosomes-X and Y in human (44A+XY), so two types of gametes are formed during sperm formation through meiosis, Y containing (22A+Y) and X containing (22A+X).
Females contain 44 autosomes and two X chromosomes. So, female can produce only one type of female gamete (22A+X) through meiosis.
Males are called heterogametic as they produce two types of gametes and females are called homogametic as they produce only one type of gamete.
Embryo produced by fusion of Y chromosome containing sperm and female gamete develops into a male. On the other hand embryo produced by fusion of X chromosome containing sperm and female gamete develops into a male.

Long Answer Type Questions

1. Describe the method of sex determination in human.

Ans. Sex determination in human

Sex determination in human is controlled in two ways-primary sex determination and secondary sex determination.

Primary sex determination: A normal human somatic cell carries 22 pairs of autosomes and 1 pair of sex chromosomes or allosomes. Autosomes control the bodily features and sex chromosomes play a major role in sex determination. Human female carries 22 pairs of autosomes and a pair of X chromosomes or the sex determining chromosomes. Their chromosomal distribution can be represented as 44A+XX. Human male, on the other hand, has one X and a Y chromosome as the sex determining chromosomes along with 22 pairs of autosomes. In case of male, the chromosomal set of a somatic cell is denoted as 44A+XY.

Meiotic cell division during gamete formation divides the chromosomes into two equal halves. In case of female, all gametes (ova) have identical chromosomal distribution, i.e., (22A+X). In male, two types of gametes are formed, the X-carrying gynosperm (22A+X) and the Y-carrying androsperm (22A+Y).

When an androsperm (22A+Y) fertilises an ovum (22A+X), a zygote is formed, which develops to form a male baby. On the other hand, the union of a gynosperm (22A+X) and an ovum results into the formation of a female baby. Therefore, father of a child determines his or her sex.
Secondary sex determination: After primary sex determination by sex chromosomes, male and female sex hormones play important role in development of respective gonads and expression of the secondary sex characters.

Short Answer Type Questions

1. Why human females are called homogametic?

Ans. Chromosomal distribution of human female is 44A+XX. It means, somatic cell of a human female carries 22 pairs of autosomes and a pair of X chromosomes. After meiosis, every ovum gets 22 autosomes and an X chromosome (22A+X). With respect to chromosomal type, a normal human female can produce identical gametes and is therefore called homogametic.

2. Why human males are called heterogametic?

Ans. Chromosomal distribution of human male is 44A+XY. It means, somatic cell of a human male carries 22 pairs of autosomes and two different sex chromosomes, X and Y. After meiosis of the male germ mother cell, two different types of male gametes or sperms are formed. Half of the sperms get 22 autosomes and an X chromosome (22A+X) and remaining half get 22 autosomes and a Y chromosome (22A+Y). With respect to chromosomal type, a normal human male can produce two different types of gametes and is therefore called heterogametic.

3. Mention the role of a mother in sex determination of a human baby.

Ans. Human female is homogametic. All ova carry X chromosomes, so the mother plays no role in the sex determination of a human baby.

4. What are sex-linked genes? Mention the types.

Ans. Sex-linked genes: Genes, present on either X or Y chromosomes, are known as sex-linked genes.

Types: The genes present on the X chromosome are called X-linked and those present on Y chromosome are called Y-linked genes.

5. Mention the role of a father in sex determination of a human baby.

Ans. Human male is heterogametic. He has two types of sperms, androsperm (carrying Y chromosome) and gynosperm (carrying X chromosome). Union of ovum and androsperm produces a male baby but union of ovum with a gynosperm produces a female baby. Therefore, only the father plays a role in sex determination of a human baby.

6. What is TDF gene?

Ans. In case of male of human there is a gene called testes determining factor in Y chromosome. Its alternative name is SRY and it helps in male child formation.

7. Why 22A+Y sperm is called androsperm and 22A+X is called gynosperm?

Ans. When 22A+Y sperm fuse with female gametes the embryo thereby formed, develop into a male child. So it is called androsperm as ‘andro’ means male. On the other hand, if a 22A+X sperm fuse with female gametes the embryo thereby formed develop into a female child. So it is called gynosperm as ‘gyno’ means female.

Very Short Answer Type Questions

Multiple Choice Questions & Answers [MCQ]

1. What would be the probability of having a boy and a girl child from a marriage between a male and a female?

A. 2:1

B. 3:2

C. 1:1

D. 1:2

Ans. C

2. Which of the following chromosomal sets applicable for a normal human male?

A. 44A + XX

B. 44A + XY

C. 44A + XXY

D. 44A + XYY

Ans. B

3. The chromosomal setup of a normal human female is-

A. 44A + XX

B. 44A + XY

C. 22A + X

D. 22A + Y

Ans. A

4. Number of chromosomes in a normal human somatic cell is-

A. 44

B. 23

C. 22

D. 46

Ans. D

5. Number of autosomes in a normal human somatic cell is-

A. 44

B. 1

C. 2

D. 46

Ans. A

6. Number of autosomes in a normal human germ cell is-

A. 44

B. 22

C. 23

D. 46

Ans. B

7. The sex chromosome present in human male gamete is-

A. X or Y

B. Only X

C. Only Y

D. X and Y

Ans. A

8. Number of sex chromosomes present in a normal human somatic cell is-

A. 46

B. 1

C. 44

D. 2

Ans. D

9. Number of chromosomes in the germ mother cell of human is-

A. 46

B. 23

C. 44

D. 22

Ans. A

10. Determination of sex by the qualitative character of chromosomes, is known as-

A. Primary sex determination

B. Secondary sex determination

C. Both A and B

D. Tertiary sex determination

Ans. A

11. Which of the following does not denote a human sperm?

A. 22A+X

B. 22A+Y

C. n

D. 44A+XY

Ans. D

12. Which of the following denotes androsperm?

A. 22A+X

B. 22A+Y

C. 22A+Z B

D. None of the above

Ans. B

13. Which of the following gametes obtained from male is responsible for girl child?

A. 22A+Y

B. 22A+X

C. 44A+Y

D. 44A+X

Ans. B

14. A man has three girl child, the chance percentage of fourth child to be a girl is-

A. 25%

B. 50%

C. 75%

D. 100%

Ans. B

Answer in a single word or sentence

1. A male gamete carries 22A+Y chromosomes. What will be the sex of the progeny obtained after its fertilisation?

Ans. If a male gamete carries 22A+Y chromosomes, the progeny will be a male after its fertilisation.

2. What are holandric genes?

Ans. The genes, which are present on Y chromosome, especially in mammals, are called holandric genes. Gene responsible for hairy pinna is an example of holandric gene.

3. Give an example of Y-linked character.

Ans. Hairy pinna in human males is an example of Y-linked character.

4. What is sex determination?

Ans. The mechanism of determining sex of an organism is known as sex determination.

5. What is the name of Y chromosome carrying sperm?

Ans. Y chromosome carrying sperm is known as androsperm.

6. What is the name of X chromosome carrying sperm?

Ans. X chromosome carrying sperm is known as gynosperm.

7. What will be the sex of a human baby if the X chromosome carrying sperm of the father unites with an ovum of the mother?

Ans. By the union of an X chromosome carrying sperm of a father and an ovum of the mother, a female baby will be born.

8. Which sperm of the father is responsible for the birth of a girl child?

Ans. An X chromosome carrying gynosperm of father is responsible for the birth of a girl child.

Fill in the blanks

1. The other name of sex chromosome is ………..

Ans. Allosome

2. Considering the type of gamete production, males are ……….. in nature.

Ans. Heterogametic

3. Considering the type of gamete production, females are ……… in nature.

Ans. Homogametic

4. Y chromosome is also known as ………….

Ans. Androsome

5. SRY is located on …………. chromosome.

Ans. Y

State true or false

1. Human sex chromosomes are of two types.

Ans. True

2. Human germ cells carry 22 autosomes.

Ans. True

3. The chromosomal distribution in a human female mother cell is 44A+XX.

Ans. True

4. The chromosomal distribution of androsperm is 22A+Y.

Ans. True

5. The chromosomal distribution of gynosperm is 44A+X.

Ans. False

6. Both human males and females are heterogametic in nature.

Ans. False

7. If a human male gamete has 22A+Y chromosomes, after fertilisation it will produce a male offspring.

Ans. True

8. A pair of sex determining sex chromosomes are present in the ovum of human.

Ans. False

TOPIC – 2

SOME GENETIC DISEASES

SUMMARY

There are some genetic diseases like-Thalassemia, Haemophilia, Colour blindness seen in human population.
Thalassemia is an autosomal recessive disease. It is mainly of two types-a and B thalassemia. On the basis of severity it is of two types-Highly severe thalassemia major and relatively less severe thalassemia minor.
In thalassemia, globin protein synthesis is disturbed resulting in Anaemia. Due to high accumulation of iron, deformities in bone are generated.
Haemophilia is an X linked disease in which due to absence of blood clotting factor, blood clotting does not take place.
Haemophilia on the basis of severty is of three types-(i) Light haemophilia [Blood clotting factor 5-50%] (ii) Moderate haemophilia [Blood clotting factor 1-5%] (iii) Severe haemophilia [Blood Clotting factor <1%]
On the basis of the type of blood clotting factor that is absent, haemophilia is of 3 typesHaemophilia A, haemophilia B or Christmas disease and haemophilia C.
Colour blindness is another X linked recessive disease where the affected person can not identify blue, green or red colour.
Cololur blindness is of three types-Protanopia [person can not recognise red colour], Deuteranopia [person can not recognise green colour], Tritanopia [person can not recognise Blue colour].
The inheritence pattern of haemophilia, thalassemia and colour blindness can be calculated by genetic cross.
Genetic counselling is important to prevent genetic disease. Through genetic counselling the chance percentage of a disease can be calculated.

Long Answer Type Questions

1. What is thalassemia? Briefly describe different types of thalassemia.

Ans. Thalassemia

The genetic blood disorder, in which any of the globin peptide chains of haemoglobin is not synthesised at all or produced in much less quantity than normal, is known as thalassemia. In this disease, quantity of haemoglobin is reduced, RBC becomes smaller and abnormally shaped.

Types of thalassemia

Two types of thalassemia are seen in human. These are— α-thalassemia and β-thalassemia.

α-thalassemia: In this type of thalassemia, synthesis of α-globin peptide chain of haemoglobin is either reduced or stopped. In 16th homologous chromosome pair, there are two genes (HBA1 and HBA2) and their two sets of alleles to control α-globin peptide synthesis. If mutation occurs in one set of allele, α-thalassemia minor occurs. When both sets of alleles are mutated, the most severe, a-thalassemia major occurs.
β-thalassemia: If synthesis of β-globin peptide chain of haemoglobin is reduced or stopped in the body, a person suffers from β-thalassemia. A pair of alleles of HBB gene is located on 11th homologous pair of chromosomes of a human cell responsible for β-globin peptide synthesis. In case of mutation in one of the alleles, β-thalassemia minor occurs. If both the alleles undergo mutation, β-thalassemia major occurs. American physician Thomas Benton Cooley discovered β-thalassemia, hence this disease is also known as Cooley’s anaemia.

2. Mention the symptoms of thalassemia. Briefly describe the cause of thalassemia.

Ans. Symptoms of thalassemia

[1] Severe anaemia due to reduced synthesis of haemoglobin. [2] Rapid breakdown of RBC leads to release and accumulation of iron in different organs, resulting into their dysfunction. [3] Excessive proliferation of bone marrow leads to deformity of bones, especially of face and skull. [4] Enlargement of liver and spleen occurs. It leads to jaundice, stunted growth and weakened immune system.

Cause of thalassemia

Thalassemia occurs due to mutation in the globin-synthesising genes. The haemoglobin molecule is composed of two a and ß-globin peptide chains. The genes for synthesis of a and ß-globin are located on 16th and 11th autosome of a human cell. The mutant a and ß-globin genes hinder the synthesis of respective globin chains, resulting into abnormal haemoglobin that leads to thalassemia.

3. What is haemophilia? Briefly describe the different types of haemophilia.

Ans. Haemophilia

Haemophilia is a genetic disorder, caused by an X chromosome-linked mutant gene, in which bleeding time from any wound is so prolonged that a person suffers from a life threatening level of blood loss. Mutation in a single gene on X-chromosome causes this disease in males, while mutation in two genes on both the X-chromosomes will cause haemophilia in females.

Types of haemophilia

In humans, two types of haemophilia are seen, these are-

Haemophilia A or classical haemophilia: In case of deficiency of a blood coagulating factor, Factor VIII or anti-haemophilic factor (AHF) in plasma, this serious type of haemophilia occurs. In our country, 80% haemophilic persons suffer from this particular disease.
Haemophilia B or Christmas disease: Deficiency of a blood coagulating factor called factor IX or Christmas factor or plasma thromboplastin component (PTC) in plasma, causes this type of haemophilia. This is not as deadly as haemophilia A. In India, 20% haemophilic persons suffer from haemophilia B. This disease was first detected in a person named Stephen Christmas. Therefore, this is also known as Christmas disease.

4. Mention the symptoms and causes of haemophilia.

Ans. Symptoms of haemophilia

Based on intensity, haemophilia may be classified into three different types-mild, moderate and severe haemophilia, which have different symptoms, as mentioned below.

Symptoms of mild haemophilia: The symptoms of mild haemophilia remain suppressed for a long time. With ageing, the problem, of blood-clotting appears slowly. The problem of bleeding becomes prominent during surgical operations or major injury.
Symptoms of moderate haemophilia: Symptoms of moderate haemophilia appear since birth. The patients suffer from prolonged bleeding. Internal haemorrhage occurs in bone joints. Swelling of joints and joint stiffness are also seen.
Symptoms of severe haemophilia: Patients suffering from severe haemophilia often bleed for no apparent reason, known as spontaneous bleeding. In case of severe haemophilia, profuse internal haemorrhage occurs in bone joints resulting into serious joint deformity (hemarthrosis). Besides, haemorrhage also occurs from nasal mucosa, within the skull, which may result into paralysis, even death of the patient.

Causes of haemophilia

The causes of haemophilia A and haemophilia B are mentioned below.

Cause of Haemophilia A or classical haemophilia: Deficiency of blood coagulating factor, called factor VIII or anti-haemophilic factor (AHF) in blood.
Cause of Haemophilia B or Christmas disease: Deficiency of blood coagulating factor, called plasma thromboplastin component (PTC) or factor IX in blood.

5. Mention the types and cause of colour blindness.

Ans. Types of colour blindness

Different types of colour blindness are seen in human population.

Protanopia or red colour blindness: In this disease, an individual cannot detect red colour. They see red as black or deep brown, orange-yellow-green as different shades of yellow and violet as blue.
Deuteranopia or green colour blindness: In case of deuteranopia, one cannot detect green colour. Deutaronopes cannot detect red, orange and yellow properly but their colour vision is better than protanopes.
Tritanopia or blue colour blindness: In blue colour blindness, a person cannot detect blue colour.

Cause of colour blindness

Colour detection in human eye depends upon the cone cells of retina. There are three types of cone cells in human retina, which are sensitive to red, green and blue colours. These cells contain separate photopsin pigments to sense the wavelengths of red, green and blue lights. Synthesis of red and green photopsin pigments are controlled by X-linked genes, whereas, the blue photopsin synthesis is controlled by an autosomal gene. In case of mutation in these genes, respective colour blindness occurs.

6. What is meant by genetic counselling? Discuss the role of genetic counselling in combating thalassemia.

Ans. Genetic counselling

By analysing the history of genetic diseases of family members and performing some genetic tests, the probability of any genetic disorder being transmitted to the future generations can be predicted. Based on these investigations, a pre-marriage suggestion is provided to a couple by the genetic counsellor so that they can have a healthy offspring. This is known as genetic counselling.

Thalassemia and genetic counselling

Thalassemia is an inherited genetic disease. Therefore, genetic counselling is needed to combat this disease. In this disease, haemoglobin is synthesised in insufficient amount and thus oxygen transportation is hampered. As a result, huge quantities of iron accumulate in the heart, liver and endocrine glands of the body. Therefore, genetic screening of haemoglobin synthesising genes must be done before marriage in families with histories of thalassemia. Using this data, the probability of children having thalassemia can be reduced. With the help of genetic counselling, the probable percentages of offsprings having thalassemia major or minor from thalassemia minor parents can be determined. Thus genetic counselling plays very important role in combating thalassemia.

7. How is genetic counselling performed? Mention the importance of genetic counselling.

Ans. Method of genetic counselling

Generally, a genetic counsellor can offer genetic counselling. This counselling includes the following steps [1] At first, the counsellor collects the history of genetic diseases of different family members and related bloodlines. The collected data is then analysed to detect genealogical trend of any disease. [2] Next, the cells or blood samples of the concerned individual are collected and tested in laboratories to find any genetic abnormality. [3] If any person is found with genetic abnormality, the same tests are performed on his or her partner. [4] After analysing the genetic status of both the partners, the chance of inheritance of any disease and its expected intensity are estimated. [5] Now, the couple is explained about the genetic status of their expected baby, either before their marriage or before conceiving. [6] If a foetus is found positive to any serious genetic disease, the parents are advised for medical termination of pregnancy.

Importance of genetic counselling

Occurrence of thalassemia, haemophilia and some other genetic diseases may be determined by genetic counselling. Genetic counselling has been proved effective if-[1] Both or any of the partners carries thalassemia causing genes. [2] The parents are aged, especially when the mother is in her forties. [3] Genealogical lines show any history of thalassemia or other genetic diseases. [4] Foetal death occurs or baby is born with any genetic disorder.

Short Answer Type Questions

1. Name two autosomal and two sex linked hereditary diseases.

Ans. Two autosomal hereditary diseases arethalassemia and albinism.

Two sex linked hereditary diseases arehaemophilia and colour blindness.

2. What is thalassemia?

Ans. Thalassemia is an autosomal hereditary disease caused due to abnormal synthesis of globin peptide chains of haemoglobin. Formation of haemoglobin in a thalassemic patient is either stopped or reduced. RBC of a thalassemic patient is smaller in size and of shorter life span (normal life span of RBC is 120 days) and the patient suffers from severe anaemia.

3. What is thalassemia major?

Ans. When both α and B-globin chains of haemoglobin are incompletely formed due to genetic mutation in both a and ß-globin genes located on 16th and 11th chromosomes respectively, the disease that occurs, is known as thalassemia major.

4. What is haemophilia?

Ans. Haemophilia is a hereditary haemorrhagic disease, caused by an X-linked recessive gene. this disease, blood lacks the capacity to coagulate and a patient may bleed to death even due to a small cut. This disease occurs due to deficiency of any one of the two blood coagulating factorsfactor VIII and factor IX.

5. What is thalassemia minor?

Ans. When any one of a or ß-globin chains of haemoglobin is incompletely formed due to mutation i.e., there is one defective allele, the disease that occurs, is called thalassemia minor.

6. What are the different types of haemophilia occurring in man?

Ans. Generally, two types of haemophilia occur in man. These are haemophilia A and haemophilia B. Besides, there is another variety of haemophilia, seen among a few people. This is known as haemophilia C.

7. What is the cause of haemophilia A?

Ans. In case of a specific recessive gene mutation in X chromosome, a blood-coagulating factor, namely Factor VIII or anti-haemophilic factor (AHF) is not synthesised in the body. Deficiency of AHF prevents blood coagulation and causes haemophilia A.

8. Why is haemophilia more common among males?

Ans. Haemophilia is an X-linked recessive genetic disorder. It is more common among males because they inherit only one X-chromosome. Since males carry one X-chromosome and one Y- chromosome, they develop symptoms of the disease if the single X-chromosome carries the recessive mutant allele.

9. Why a carrier female of haemophilia A gene does not get affected by the disease?

Ans. Somatic cells of a female carry two X chromosomes. When one of the two X chromosomes carries the recessive allele for haemophilia but the other carries the normal dominant allele, the female becomes a carrier. This normal dominant allele suppresses the recessive haemophilia allele and prevents the female from being haemophilic. Therefore, a female, carrying a single recessive allele for haemophilia is not affected by haemophilia A.

10. What is the cause of haemophilia B?

Ans. In case of a specific recessive gene mutation in X chromosome, a blood-coagulating factor, namely factor IX or Christmas factor is not synthesised in the body. Absence or deficiency of this factor prevents blood coagulation and causes Haemophilia B.

11. What is criss-cross inheritance?

Ans. The transmission of a genetic character from father to daughter and from mother to son is known as criss-cross inheritance. All X-linked characters show criss-cross inheritance. In this type of inheritance, the following inheritance pattern is seen-Father → Grandson Daughter → Great grand daughter.

12. Name few genetic disorders that can be prevented by undergoing genetic counselling.

Ans. Genetic counselling is considered by couples before marriage to prevent the occurrence of any genetic disorder in their children. The examples of the genetic diseases that can be prevented by undergoing genetic counselling are thalassemia, haemophilia, colour blindness, etc.

13. What is colour blindness?

Ans. Colour blindness is a genetic disorder in which a person cannot detect red, green or blue colour. Red-green colour blindness occurs due to X-linked recessive mutation, but blue colour blindness is an autosomal recessive disorder.

14. What is monochromacy?

Ans. In human retina, there are three types of colour sensitive cone cells, which can detect red, green and blue colours separately. If 2 or 3 types of the pigmented cone cells are absent the colour detecting ability is totally lost. Such a person can view the world in black and white. This rare type of colour blindness is known as monochromacy.

15. What is dichromacy?

Ans. If out of the three types of cone cells, two remain active and one inactive, a person cannot detect that particular single colour. This type of colour blindness is called dichromacy. The common red, green or blue colour blindness are the examples of dichromacy.

16. Write down the symptoms of Thalassemia.

Ans. [1] Tiredness and fatigue. [2] Malformation of bone, specially bone of face. [3] Blackish urine. [4] Yellowish colouration of skin and retardation of growth.

17. Which of the three organs of human body are damaged due to thalassemia?

Ans. Liver, spleen and heart of human is damaged in thalassemia due to high accumulation of iron.

18. Why haemophilia is more expressed in male than female?

Ans. Haemophilia is a sex-linked recessive disorder whose gene is present on X chromosome. Males have only one X chromosome so if it fears the allele for haemophilia then it is always expressed. But females have two X chromosomes. So for being haemophilic, each of the two X chromosomes must have the allele for haemophilia, otherwsie the disease is not expressed in females, so haemophilia is more expressed is females than in males,

19. If the mother is haemophilie carrier and father is haemophilic then what will be the nature of spring? Show it with a cross.

Ans.

The nature of the offspring: 50%-haemophilic, 25%-Carrier, 25%-Normal.

20. What will be the genotype of father of a haemophilic girl?

Ans. As both the chromosomes of a haemophilic girl contain allele for colour blindness. So the father must have the X chromosome with allele for colour blindness. He also possess Y chromosome. So his genotype is XCY.

21. If the mother is colour blind then the son is always colour blind-Justify.

Ans. A colour blind mother always has two X chromosomes, each with allele for colour blindness, i.e. genotype is XCXC. A son get his X chromosome from the mother and Y chromosome from father. So he will get a X chromosome from mother and his genotype will be XCY. Thus he will be colour blind.

22. What is genetic counselling?

Ans. Genetic counselling is a process through which by analyzing the history of genetic disease in a family and by genetic test, prediction is made about the chances of the offspring to be normal or with disease.

23. What is the importance of genetic counselling?

Ans. [1] It prevents the birth of child with a genetic disease. [2] It can help in calculating the chances of genetic disease of a child.

24. Show with the help of cross, how colour blindness is inherited.

Ans. Colour blindness is a genetic disorder, caused by an X chromosome linked mutant gene. Mutation in a single gene causes this disease in males, while mutation in two genes on both the Xchromosomes will cause colour blindness in females. So, when a colour blind woman is married to a normal man, their sons will be colour blind while daughters will be carrier of colour blindness. The cross is schematically represented below.

25. A daughter is born to a woman carrier for the colour blind disease who married a colour blind man. What would be the probability of expression of colour blindness in that girl child? Analyse your answer.

Ans.

There will be 50% chance of the daughter being colour blind. This is because the X chromosome that she will obtain from her father will definitely bear allele for colour blindness. However, the X chromosome that she will obtain from her mother may either bear the allele for colour blindness or that for normal vision. So, she has 50% chance of being colour blind.

26. Write the names of two genetic diseases which are expressed in human populations.

Ans. Two genetic diseases expressed in human population are-thalassemia and haemophilia.

27. Give your opinion about probable suggestions which can be given to a pair of contenders before marriage in order to prevent the spread of a genetic disease from the society already known to you.

Ans. The pair of contenders should be suggested to test whether they are carrier or have any particular disease. If both are carrier for autosomal disease or one is carrier and other have the disease then the marriage should be cancelled. If they both are normal or if one is normal and other is carrier then they can marry.

28. One day students read an article in newspaper on thalassemia and were very scared to know the fate of a thalassemic patient. Write what kind of measure they can take to eradicate this disease from the population.

Ans. The measure they can take to eradicate this disease from the population are-

Genetic counselling before marriage and not to conduct marriage between carrier male and female or affected and normal individual.
If genetic counselling is not done before marriage then it must be done before conceiveing a child and not to conceive in sensitive case.

Very Short Answer Type Questions

Multiple Choice Questions & Answers [MCQ]

1. A sudden and permanent change genes is called –

A. Adaptation

B. Inversion

C. Mutation

D. Recombination

Ans. C

2. A symptom of thalassemia is-

A. Scurvy

B. Anaemia

C. Rickets

D. Malaria

Ans. B

3. Anti-haemophilic globulin factor is known as-

A. Factor VII

B. Factor VIII

C. Factor IX

D. Factor X

Ans. B

4. Plasma thromboplastin antecedent is also known as-

A. Factor VII

B. Factor VIII

C. Factor XI

D. Factor X

Ans. C

5. Thalassemia minor is also known as-

A. Thalassemia trait

B. Thalassemia hydrops

C. Cooley’s anaemia

D. Thalassemia child

Ans. A

6. Which of the following is a wrong statement about thalassemia ?

A. It is a sex chromosome-linked trait

B. It is a hereditary disease

C. In this disease structural deformity of haemoglobin is seen

D. In this disease iron is deposited in blood

Ans. A

7. The disease, where a patient faces problem of haemorrhage is known as-

A. Leukaemia

B. Haemophilia

C. Thalassemia

D. Colour blindness

Ans. B

8. Thalassemia major is also known as-

A. Cooley’s anaemia

B. Cooley’s syndrome

C. Down’s syndrome

D. Turner’s syndrome

Ans. A

9. The human chromosome that carries a-globin gene is-

A. 11th

B. 12th

C. 14th

D. 16th

Ans. D

10. The human chromosome that carries β-globin gene is-

A. 11th

B. 12th

C. 14th

D. 16th

Ans. A

11. The colours, which a colour blind person is unable to detect, are-

A. Violet-yellow

B. Indigo-blue

C. Red-green

D. Orange-yellow

Ans. C

12. An example of autosomal hereditary disease is –

A. Haemophilia

B. Colour blindness

C. Thalassemia

D. Scurvy

Ans. C

13. Which of the following is a sex-linked hereditary disease?

A. Anaemia

B. Scurvy

C. Thalassemia

D. Haemophilia

Ans. D

14. An example of X-linked inherited disease is

A. Colour blindness

B. Night blindness

C. Thalassemia

D. Malaria

Ans. A

15. The type of colour blindness, in which a person cannot detect green colour, is-

A. Haemophilia

B. Thalassemia

C. Protanopia

D. Deuteranopia

Ans. D

16. Which of the following diseases occurs mostly among males?

A. Red-green colour blindness

B. Thalassemia

C. Cancer

D. Tuberculosis

Ans. A

17. The gene causing colour blindness is located on-

A. X chromosome

B. Y chromosome

C. Z chromosome

D. M chromosome

Ans. A

18. The other name of blood coagulating factor VIII is-

A. ABB

B. HBA

C. PTA

D. AHF

Ans. D

19. The disease, caused due to abnormal structure of the globin peptide chain, is-

A. Haemophilia

B. Thalassemia

C. Malaria

D. Scurvy

Ans. B

20. Christmas disease is

A. Haemophilia A

B. Colour blindness

C. Royal haemophilia

D. Haemophilia B

Ans. D

21. The other name of blood coagulating factor IX is-

A. AHF

B. HBA

C. HBB

D. PTA

Ans. D

22. To whom should a person approach to get premarriage suggestions to avert any genetic disease in his or her offspring?

A. Psychologist

B. Genetic counsellor

C. Physician

D. Surgeon

Ans. B

23. Genetic counselling is advisable for-

A. Thalassemia

B. Malaria

C. Hepatitis

D. Diarrhoea

Ans. A

24. Deficiency of which of the following factors causes haemophilia?

A. Factor VIII

B. Factor IX

C. Factor III

D. Factors VIII & IX

Ans. D

25. The type of haemophilia carried by Queen Victoria, was-

A. Haemophilia A

B. Haemophilia B

C. Haemophilia C

D. Haemophilia D

Ans. A

26. Criss-cross inheritance occurs in case of-

A. Colour blindness

B. Diabetes

C. Anaemia

D. Scurvy

Ans. A

27. The main problem in haemophilia is-

A. Disability of colour detection

B. Internal haemorrhage

C. Internal blood coagulation

D. High fever and inflammation

Ans. B

28. The plasma protein, which is not synthesised in haemophilia, is –

A. Albumin

B. Globulin

C. Fibrin

D. Chitin

Ans. C

29. The disease in which function of liver and heart is hampered due to iron accumulation-

A. Haemophilia

B. Anaemia

C. Thalassemia

D. Blood Cancer

Ans. C

30. Which of the following is not true for thalassemia?

A. It is a sex linked disease

B. This is a genetic disease

C. In this disease haemoglobin is not formed properly

D. Iron is accumulated in this disease

Ans. A

31. The reason behind Cooley’s anaemia is-

A. Mutation

B. Adaptation

C. HbS

D. HbF

Ans. A

32. Cooley’s anaemia is-

A. α thalassamia major

B. α thalassemia minor

C. β thalassemia major

D. β thalassemia minor

Ans. C

33. If both the parents are carrier of thalassemia then the chance percentage of their child to be thalassemic is-

A. 100%

B. 75%

C. 50%

D. 25%

Ans. D

34. Which of the following is not controlled by the autosomal gene of human?

A. Roller tongue

B. Haemophilia

C. Thalassemia

D. Attached ear hole

Ans. B

35. The factor responsible for haemophilia A is

A. VI

B. VII

C. VIII

D. IX

Ans. C

Answer in a single word or sentence

1. Who coined the term ‘thalassemia’ and when?

Ans. Whipple and Bradford coined the term ‘thalassemia, in the year 1932.

2. What percentage of iron is present in haemoglobin?

Ans. Haemoglobin contains 0.34% iron.

3. Name the group of diseases caused due to defective haemoglobin.

Ans. Group of diseases caused due to defective haemoglobin is called haemoglobinopathy.

4. Which protein is produced in reduced quantity in a thalassemia patient?

Ans. Haemoglobin, the conjugated protein, is produced in reduced quantity in a thalassemia patient.

5. Which metal accumulates in the body of a thalassemia patient due to rapid destruction. of red blood cells?

Ans. Huge quantity of iron accumulates in the body of a thalassemia patient due to rapid destruction of red blood cells.

6. Which organs of the body are mostly affected due to accumulation of excessive iron?

Ans. Heart, liver, spleen and the endocrine system are mostly affected due to accumulation of excessive iron.

7. How much oxygen is carried by normal haemoglobin? m

Ans. 1 g of normal haemoglobin carries 1.34 ml of oxygen.

8. What is the cause of malformation of a and β chains in haemoglobin of a thalassemia patient?

Ans. Due to mutation in a and β-globin genes, a and β-peptide chains in haemoglobin of a thalassemia patient are malformed.

9. What is a thalassemia?

Ans. The type of thalassemia, caused due to incomplete formation of a-chains of haemoglobin, is known as a thalassemia.

10. What is β thalassemia?

Ans. The type of thalassemia, caused due to incomplete formation of β-chains haemoglobin, is known as β thalassemia.

11. In which disease, bleeding does not stop due to non-coagulation of blood?

Ans. In haemophilia, bleeding does not stop due to non-coagulation of blood.

12. Name the disease caused due to deficiency of clotting factor VIII in blood.

Ans. Haemophilia A is caused due to deficiency of clotting factor VIII in blood.

13. Name the disease caused due to deficiency of clotting factor IX in blood.

Ans. Haemophilia B is caused due to deficiency of clotting factor IX in blood.

14. What is the other name of haemorrhagic disease?

Ans. The other name of haemorrhagic disease is haemophilia.

15. Which type of disease is haemophilia B?

Ans. Haemophilia B is an X chromosome-linked recessive hereditary disease.

16. Why does haemophilia occur?

Ans. Haemophilia occurs due to a recessive mutation in an X-linked gene.

17. In which chromosome of human cell does the haemophilia gene occur?

Ans. Haemophilia gene occurs in X chromosome of human cell.

18. What is the other name of haemophilia A?

Ans. The other name of haemophilia A is classical haemophilia.

19. Name the disease-causing gene, which was first carried by Queen Victoria of Britain.

Ans. Queen Victoria of Britain was the first to the carry disease-causing gene of haemophilia B.

20. Who are called protanopes?

Ans. People who are suffering from protanopia and hence, cannot detect red colour, are called protanopes.

21. Who are called deuteranopes?

Ans. People who are suffering from deuteranopia and hence, cannot detect green colour, are called deuteranopes.

22. Who are called tritanopes?

Ans. People who are suffering from tritanopia and hence, cannot detect blue colour, are called tritanopes.

23. Which type of male baby is expected from a colour blind mother and a normal father?

Ans. A colour blind mother and a normal father will have a colour blind son.

24. Which type of thalassemia is predominant in India?

Ans. a thalassemia

25. Which type of haemophilia is not a sex-linked disease?

Ans. Haemophilia C is caused by an autosomal mutation and hence, not a sex-linked disease.

26. What is reason behind the name ‘thalassemia’?

Ans. The disease thalassemia was first discovered in the people living near mediterranean sea. In Latin language sea is called ‘thalassa’ and so the disease is called thalassemia.

27. Which chromosomes contain genes for production of a and ß chain of globin protein?

Ans. a chain-chromosome 11 and β chain-chromosome 16

Fill in the blanks

1. The genetic disease, which was expressed for the first time in the British royal family, is ……….

Ans. Haemophilia

2. Thalassemia is a ……….. disease.

Ans. Genetic

3. If the synthesis of ………. is hampered, a person develops severe anaemia.

Ans. Haemoglobin

4. Regular blood transfusion increases ……….. content in the body of a thalassemia patient.

Ans. Iron

5. Haemophilia is a/an ………… chromosome linked genetic disease.

Ans. X

6. Almost ………. % haemophilia is caused by the deficiency of AHF.

Ans. 80

7. Haemophilia B or …………… disease is caused by the deficiency of blood clotting factor IX.

Ans. Christmas

8. The colour detecting cells of retina are known as ………… cells.

Ans. Cone

9. The gene responsible for blue colour blindness is a/an ……….. gene.

Ans. Autosomal

10. In ………… hromosome of human β globin gene is present.

Ans. 11th

11. Cooley’s anaemia is ………….

Ans. β thalassemia major

12. The cells of eye associated with colour recognition is ………..

Ans. Cone cell

13. All ……….. will be colour blind if mother is colour blind and father is normal.

Ans. Sons

14. A disease in human population caused by recessive gene located in ‘X’ chromosome is ………..

Ans. Haemophilia

15. ………. is a disease created by sex-linked gene.

Ans. Haemophilia

State true or false

1. Malaria, AIDS. hepatitis etc., are examples of genetic diseases.

Ans. False

2.In thalassemia, bone marrow proliferates at an excessive rate.

Ans. True

3. In thalassemia, synthesis of globin protein is hampered.

Ans. True

4. aemophilia is an autosome linked genetic disorder.

Ans. False

5. Haemophilia A is caused by restricted synthesis of factor VIII.

Ans. True

6. Haemophilia B is caused by restricted synthesis of factor X.

Ans. False

7. A protanope is unable to detect red colour.

Ans. True

8. The gene responsible for blue colour blidness is located in 8th chromosome.

Ans. False

9. The pre-marriage suggestion to a couple for having a baby without any genetic disorder, is known as genetic counselling.

Ans. True

10. In an anaemic pattient, oxygen transport is seriously hampered.

Ans. True

11. Night blindness is an X chromosome linked disease.

Ans. False

12. Blood coagulation process is hindered in a haemophilic patient.

Ans. True

13. Rod cells of human retina help in colour detection.

Ans. False

14. In case of serious haemophilia, blood contains 1% more blood coagulating factors than normal.

WNA24

WBBSE 10th Class Science Solutions Science & Environment Chapter 3 Heredity and Some Common Genetic Diseases

West Bengal Board 10th Class Science Solutions Science & Environment Chapter 3 Heredity and Some Common Genetic Diseases

WBBSE 10th Class Life Science & Environment Solutions

Leave a Reply Cancel reply