Chapter: Principles of Inheritance and Variations.

Very short answer questions (1 Mark Questions )

1. Name the Mendel’s law which states that gene pairs assort randomly or independently of

one another?

Ans: The Law of Independent Assortment.

2. What is Aneuploidy?

Ans: Addition or loss of one or more chromosomes to the complete diploid chromosome

complement of an organism

3. What is point mutation? Give an example?

Ans: Point mutation occurs due to change in a single base pair of D.N.A. Ex.Sickle Cell

Anemia.

4. What is the cytological basis of Down’s syndrome?

Ans: It is Trisomy of 21 chromosome / 45+ XX/ 45+ XY.

5. Define test cross.

Ans: A cross between F1 generation and a recessive parent.

6. A child is born with XXY chromosomal constitution, what will be the syndrome?

Ans: Klinefelter’s Syndrome

7. What is Gynaecomastia ?

Ans: Development of breast in males

8. How many autosomes are found in a single mature human sperm or ovum?

Ans: 22 Autosomes

9. What is female heterogamy ?

Ans: It is the phenomenon where females produce two different types of gametes or ova,

with reference to sex chromosomes.

10. What is frame shift mutation?

Ans: Deletion or addition of one or two base pairs or a segment of DNA in a gene, leads to

change in reading sequence of triplet codons on m-RNA. This results in wrong polypeptide

chain synthesis.. In thalassemia, an inherited blood disorder, the B chain of hemoglobin

changes due to frame shift mutation.

11. What is multiple allelism?

Ans: Occurrence of a gene in more than two allelic forms is multiple allelism . An individual

possess only two of these alleles on homologous chromosomes.. Ex. Alleles of ABO blood

types in human.

12. Define the terms genetics and inheritance.

Ans: Genetics is a branch of science which deals with inheritance as well as the variation of

characters from the parents to offspring. Inheritance is a process by which characters are

passed on from parents to offspring through genes.

13. What is emasculation?

Ans: Removal of anthers from by sexual flowers, to prevent self pollination.

14. What is true breeding line for a trait?

Ans: It is a homozygous individual, obtained by continuous self-pollination for several

generations.

15. What is linkage?

Ans: Closely placed genes on a chromosome tend to inherit together as a block from parents

to offspring. This phenomenon is linkage.

16. What is crossing over?

Ans: Mutual exchange of genetic material between non-sister chromatids of homologous

chromosomes during the process of meiosis.

17. A garden pea plant produced axial white flowers. Another of the same species produced terminal violet flowers. Identify the dominant traits. Ans: Axial , violet flowers

18. Define pleiotrophy with is an example .

Ans: Single gene produces more than one effect or control more than one phenotype. 19. How is sex determined in grasshopper?

Ans: By XO type sex determining mechanism. The males have only one X chromosome,

besides the autosomes, whereas the females have a pair of X chromosomes

20. In the following pedigree chart, state if the trait is autosomal dominant, autosomal recessive or sex linked. Give a reason for your answer.

Ans: It is autosomal dominant because the trait is seen in both parents and offspring; and also

both sons and daughters are affected

21. Name one autosomal dominant and one autosomal recessive Mendelian disorder in

humans.

Ans: autosomal dominant – myotonic dystrophy; one autosomal recessive- sickle cell

anaemia.

22. What are the advantages of pedigree analysis?

Ans: It provides a strong tool to trace the inheritance of a specific trait or abnormality or

disease. It gives the history of a character in a family.

23. Which of the following traits in Garden Pea are considered to be recessive in Mendel’s

experiment: Axial flowers, Green seed, Green pod, violet flowers?

Ans: Green seed

24. Which of the following cross is the test cross:

TT X Tt ; TT X TT; Tt X Tt; Tt X tt

Ans: Tt X tt

25.

What is this Mendel’s deviation technically termed.

Ans: Pleiotropy

26. When a cross is done between a red flowered plant with a white flowered one, pink

flowered off springs are produced in F1 generation. Name the phenomenon behind this

process?

Ans: Incomplete dominance.

27. The human genome consists of ___ linkage groups.

Ans: 23

28. State which law of Mendelian inheritance is expressed in the following diagram?

Ans:- Law of Segregation

29. What type of allele produces its effects only in homozygous individual . a) dominant, b) recessive, c) incomplete dominant , d) incomplete recessive.

Ans. recessive 30. Name two organisms where males are heterogametic. Ans. Human and Drosophilla 31. Scientific name of garden pea is ________________ Ans. Pissum sativum

32. Tendency of gene to link together in a same locus is called ___________________ Ans. Linkage

33. Name two Mendelian disorder that are sex- linked

Ans. Haemophilia , colour blindness

Short answer questions (2/ 3 Marks )

34. What is incomplete dominance, explain with punnet square?

Or

When a red flowered Antirrhinum plant was crossed with a white flowered Antirrhinum

plant the F1 offspring had pink flowers. Mention

a) The genotype of F1plant. b) The reason why it did not bear the parental red or white

flower colours.

Ans: Incomplete dominance: In a Hybrid the allelic pair responsible for a trait is in

heterozygous condition. Neither of the alleles is recessive nor dominant and produces an

intermediate phenotype. Ex: flower colour in Snapdragon/ Antirrhinum

Punnet Square

Phenotypic Ratio- 1:2:1 Genotypic Ratio- 1:2:1

35. Why did Mendel select pea plant for his genetic experiments?

Gamete R r

R RR ( Red)

Rr ( Pink)

r Rr (Pink)

rr (White)

Ans: It is a annual plant with a short life cycle. So, several generations can be studied

within a short period.

Has easily observable contrasting pairs of characters.

Has bisexual flowers, hence can produce pure lines by natural self pollination.

Artificial cross pollination can be easily carried out.

36. A true breeding tall plant is crossed with a true breeding dwarf plant. F1 progeny is 100% tall and F2 has tall : dwarf in the ratio 3:1 Explain why

(i) F1 shows only one type of parental phenotype; (ii) F2 shows both parental phenotypes

Or Explain Mendel’s law of segregation with the help of a monohybrid cross.

Ans: (i) Law of dominance: The allele ‘T’ is dominant over allele‘t’.

The tall allele’T’ expresses in both heterozygous and homozygous

condition. Therefore F1 hybrids tall

(b) Law of segregation: The alleles in heterozygous condition remain together without

mixing with each other and at the time of gamete formation they separate out, only one

allele enters each gamete. Because of this, in F2 generation both the parental

phenotypes are observed.

Parents ; Tall vs Dwarf

Genotype: TT tt

Gametes: T t

F1 generation: Tt

Tall

Selfing of Fi hybrids

Tt vs Tt

Tall Tall

Gametes: T t T t

F2 generation:

Tall: Dwarf - 3:1

37. In a pea plant round seed is dominant over wrinkled seed. What will be the expected Phenotypic ratio of the offspring in a cross between

a. Heterozygous round and heterozygous round. b. Homozygous round and heterozygous round c. Heterozygous round and wrinkled

Ans: Hint: a) cross between Rr vs Rr

b) cross between RR vs Rr

c) cross between Rr vs rr

T t

T TT tall

Tt tall

t Tt tall

Tt dwarf

38. Inheritance patterns of flower colour in garden pea plant and snap dragon differs. Why is the difference observed? Explain the difference in their inheritance patterns with the help of crosses. Ans: Hint: Explain law of dominance in case of garden pea Explain law of incomplete dominance in case of snap dragon

39. In a particular plant species, majority of the plants bear purple flowers. Very few plants bear white flowers. No intermediate colours are observed. If you are given a plant bearing purple flowers, how would you ascertain that it is a pure breed for that trait? Explain.

Ans: By Test cross

Cross purple flower plant, with a (homozygous) recessive plant with white flowers

If all the flowers of the progeny of the above cross are purple, then plant is homozygous dominant i.e. pure breed.

Parents: Purple flower vs white flower

Genotype: PP pp

Gametes:

Progeny: Pp

Purple

.

.

40. Explain the phenomena of multiple allelism and co-dominance taking ABO blood

group as an example.

Ans: Multiple allelism is the phenomenon of occurrence of a gene in more than two

allelic forms on the same locus. In ABO blood group in humans’ one gene ‘I’ has three

alleles - IA, IB and i. But an individual with a specific blood group possess only two of such

alleles Ex: A group has genotype; IAIa or IAi.

Co-dominance is the phenomena in which both alleles express themselves side by side

when present together. When the genotype is IAIB the individual has AB blood group,

since both IA and IB equally influence the formation of antigens A and B.

41. A man with blood group A married a woman with B group. They have a son with AB blood group and a daughter with blood group O. Work out the cross and show the possibility of such inheritance.

Ans: Since, son has blood group AB and daughter has blood group O then the possible genotype of man will be IA i and that of female will be IB i. The desired cross would be as follows:

Parents : Man vs woman

Genotypes IAi IBi

Gametes IA, i IB, i F1 generation

gametes IA i

P P

IB IAIB

AB group IBi

B group

i IAi A group

I i O group

Thus, the F1 progeny can have all the four possible blood groups, i.e., A, B, AB and O.

42. Who proposed chromosomal theory of inheritance? What are the main concepts of it?

Ans: Sutton and Boveri proposed the theory.

Main concepts:

Genes are arranged in linear order on chromosome.

In a dipoid individual, the homologous chromosomes occur in paired condition.

So also the genes responsible for a trait occur in paired condition as they are

present on homologous chromosomes.

At the time gamete formation the paired chromosomes as well as gene pair

separate and move to gametes.

The paired condition of the chromosomes/ genes gets restored by fertilization

process.

43. Why was Drosophila selected for genetic experiments by T.H. Morgan?

Ans: It can be grown on simple synthetic medium in a lab.

It completes life cycle in short span of time.

Single mating produces large number progeny.

Phenotypic characters can be observed easily

44. T.H. Morgan, during a dihybrid cross in drosophila between white eyed, yellow bodied

female and red eyed, brown bodied male found that phenotypic ratios deviated from

expected 9:3:3:1 ratio. Explain the conclusion he arrived at.

Ans: When two genes in a dihybrid cross are located on the same chromosome, the

proportion of parental gene combinations in the progeny was much higher than the

non- parental gene combinations.

On the same chromosome also tightly linked genes show less recombination,

where as loosely linked genes show higher recombination

45. Explain the reasons for the change in the parental and non parental gene combinations in

genetic crosses. How has it been utilized in further genetic studies?

Ans: The changes in parental and non parental gene combinations are due to linkage and recombination. The frequency of gene recombinations between gene pairs on the same chromosome is used as a measure of distance between genes; it is used in mapping of chromosomes.

46. Explain sex determination mechanism in human? How is it different from birds?

Ans: In humans – male heterogamety is seen

In human XY type of sex determination is seen. Male determines the sex of new born child

Both males and females have equal number of Chromosomes i.e 46. out of these 44 are autosomes and 2 are sex chromosomes.

Males have X and Y sex chromosome. While, females have X and X sex chromosomes

Male produces two types of sperms i.e. ‘X’ and ‘Y’ sperms, hence it is heterogametic

Female produces only one type of eggs i.e. ‘X’ eggs, hence it is homogametic

When Y sperm fertilizes with X egg, a boy ( XY) is born. When x sperm fertilizes with x egg, a girl ( XX) is born.

In birds,- female heterogamety is seen

They exhibit ZW type of sex determination Female determines the sex of the offspring.

Female produces two types of eggs i.e. ‘Z’ and ‘W’ eggs, hence it is heterogametic

Male produces only one type of sperms i.e. ‘Z’ sperms, hence it is homogametic

When W egg fertilizes with Z sperm , a female(ZW) is born. When Z egg fertilizes with Z sperm , a male(ZZ) is born.

47. In our society the women are blamed for giving birth to daughters. Can you explain why

this is not correct?

Ans: Hint: Explain sex determining mechanism in human

48. What is female heterogamy? Is the egg or sperm responsible for the sex of individual in humans? Ans: Hint: Explain sex determining mechanism in birds

49. The male fruit fly and female fowl are heterogametic while the female fruit fly and the male fowl are homogametic. Why are they called so? Ans: The male fruit fly has XY sex chromosomes and produces two types of gametes hence

it is called heterogametic while female fowl has ZW sex chromosomes thereby producing

two types of gametes thus they are called heterogametic.

Female fruit fly has two X chromosomes, i.e., XX and produces similar gametes hence they

are called homogametic. Also, male fowl has two Z chromosomes and produces similar

gametes thus they are called homogametic.

50. Why is haemophilia generally observed in human males? Explain the conditions under which a human female can be haemophilic.

Or

Why is it that the father never passes on the gene for haemophilia to his sons? Explain

Ans: Haemophilia is caused due to the recessive gene on X-chromosome. Y has no allele

for this.

The male inherits Xh allele from the mother and ,he will be haemophilic with a single dose

of haemophilic allele(with the genotype XhY).

Females with single dose of haemophilic allele act as carriers (XhX).

If female with the genotype XhXh is haemophilic.She inherits the alleles, one from the

carrier mother and one from her haemophilic father.

51. A non-haemophilic couple was informed by their doctor that there is possibility of a

haemophilic child be born to them. Draw a checker board and find out the percentage of

possibility of such child in the progeny.

Ans: In the instant case mother is a carrier ( Xh X) and father is a non haemophilic (XY)

Phenotypes : Carrier mother vs normal father Genotype: (Xh X) (XY)

Gametes: Xh, X X, Y Progeny:

gametes Xh X

X XhX XX

Y XhY XY

50% daughter normal (XX) 50% daughter carrier (XhX) 50% son normal (XY)

50% son haemophilic (Xh Y)

52. A normal visioned woman, whose father is colour blind, marries a normal visioned

man.what would be the probability of her sons and daughters to be colour blind?

Ans:

Hint: Woman is carrier for colour blindness, as her father is colour blind.

Solve the problem just like question no. 40 by substituting Xh allele( haemophilic allele) with

Xc allele( colour blind allele).

53. Explain the cause of Sickle-cell Anaemia and its inheratance.

Sickle-cell Anaemia Ans: It is an autosomal linked recessive trait.

The disease is controlled by a single pair of allele- HbA and HbS .

Only the homozygous individuals for Hb S, i.e., HbSHbS show the diseased phenotype.

The heterozygous individual are carriers (HbAHbS ).

Due to point mutation, Glutamic acid (Glu) is replaced by Valine (Val) at sixth positions of beta globin chain of haemoglobin molecule.

HbS behaves as normal haemoglobin except under oxygen stress where erythrocytes lose their circular shape and become sickle-shaped. As a result, the cells cannot pass through narrow capillaries. Blood capillaries are clogged and thus affects blood supply to different organs.

54. Name a disorder, give the karyotype and write the symptoms where a human male suffers

as a result of monosomy of the sex chromosome.

Or

Name the phenomenon that leads to situations like ‘XO’ abnormality in humans. How do

humans with XO abnormality suffer? Explain.

Ans: Turner’s syndrome is the disorder caused by the absence of one of the x

chromosomes. Its karyotype will be 45+ XO.

Symptoms:

Sterile females

Rudimentary ovaries

Lack of secondary sexual characters

55. Explain the inheritance phenomenon responsible for skin colour in human.

Ans: the phenomenon is ‘Polygenic inheratance’

This polygenic trait is controlled by three different pairs of alleles( Aa Bb and Cc) and these

alleles have cumulative/additive effect on phenotype.

The person with all 6 dominant alleles ( AABBCC) has dark colour

The person with all 6 recessive alleles ( aabbcc) has white colour

The person with 3 dominant alleles ( AaBbCc) has intermediate colour

56. Explain why the phenotype and genotype ratios are the same in Mirabilis in the case of

inheritance.

Ans: It is because of incomplete dominance. The F1 progeny show intermediate character

between dominant and recessive traits. When red flowered plants are crossed with a white

flowered plants the F1 progeny produced are pink flowered. When the F1 is self pollinated

1red, 2pink and 1 white flowered plants are obtained and so F2 phenotypic and genotypic

ratios are same 1:2:1.

57. From the following diagram name the type of mutation and its possible cause?

Ans: Duplication of genes in a chromosome, This may be due to sudden change occurring

during supercoiling of DNA or synthesis or division of chromosomes.

58. Individuals suffering from sickle cell anaemia are more prone to heart attack. State why?

Ans: It is due to aggregation of red blood cells in the capillary systems and thus several

tissues suffer from severe damage due to less supply of oxygen.

59. When XHX female is crossed with XY male, what is the percentage of offsprings suffering

from haemophilia?

Ans: 25% male progeny suffer from haemophilia and 25% female are carrier.

60. How is polyploidy helpful to humans?

Ans: Polyploidy is introduced in hybridisation experiments in agriculture to obtain novel

characters. Eg:Triticum sp. (wheat) used widely is a polyploid(4n).

61. The map distance between A & B genes is 24 unit; between B & C is 22 unit and A & C is 2 unit.(a)What is the order of genes on a linkage group?(b) Write the unit of map distance. Ans: (a)

(b) Centi Morgan

62. (a) Write the genotype of each individual next to the symbol.

b) Whether this pedigree is for an autosomal recessive trait or dominant trait?

c) In this pedigree, two generations have been skipped. What can you conclude about

recessive traits skipping generations (is it possible or not)?

Ans:(a)

(b) autosomal recessive

(c) It is possible as recessive genes express only in homozygous condition and

remains suppressed in heterozygous condition. 63. Distinguish between monohybrid and dihybrid cross. Ans. Crossing between asingle con trasting character/two contrasting character. Phenotypic ratio of monohybrid cross is 3:1/ dihybrid is 9:3:3:1. 64. What is trisomy, Give an example. Ans. Three copies of a particular chromosome present in a cell, example-Down”syndrome 65. What is co-dominance, give an example.

Ans. When alleles express themselves equally,. Blood group AB. 66. Write four symptomps of Turner”s syndroms. Ans. 1)sterile female ,2)poorly developed breast 3)short stature. 4) small uterus 67. Mentions the advantages of selecting pea plant for experiment. Ans. Pea is a annual plant and cultivated in small area, pollination generally self but cross pollination may take artificially, contrasting characters are not overlapping. 68. What is Pedigree analysis? Write advantages.

Ans. It is a system to study the distribution and movement of traits in a series of

generation in a family. Sex linked disorders like Haemophilia and colour blindness will be identified and treated by Pedigree .

Long answer questions (5 Marks Questions ) 69. .What is dihybrid cross ? Explain Law of independent assortment taking example of seed

shape and seed coluor in pea plant.

Ans: Mendel’s Law of Independent Assortment: This law states that ‘ when two pairs of traits are combined in a hybrid, segregation of one pair of traits/ characters is independent of the other pair of characters’.

When round yellow seed pea plant is crossed with wrinkled green seeds pea plant, in the F1 generation round yellow seeds are produced.

When F1 hydrids are selfed, in the F2 generation we get parental as well as new combinations in 9:3:3:1 ratio. This because the alleles of seed colour assort independent to that of seed shape. Parents: Round yellow vs Wrinkled green Genotype: RRYY rryy Gametes: RY ry F1 generation: RrYy Round yellow Selfing F1 hybrids Round yellow vs Round yellow RrYy RrYy Gametes: RY, Ry, rY, ry RY, Ry, rY, ry F2 generation

gametes RY Ry rY ry

RY RRYY Round yellow

RRYy Round yellow

RrYy Round yellow

RrYy Round yellow

Ry RRYy Round

RRyy Round

RrYy Round

Rryy Round

yellow green yellow green

rY RrYy Round yellow

RrYy Round yellow

rrYy wrinkled yellow

rrYy wrinkled yellow

ry RrYy Round yellow

Rryy Round green

rrYy wrinkled yellow

Rryy wrinkled green

Phenotype:

Round yellow =9

Round green =3

wrinkled yellow=3

wrinkled green =1

46. A true breeding pea plant homozygous for axial violet flowers (AAVV) is crossed with

another pea plant with terminal white flowers (aavv).

(i)What would be the phenotype and genotype of F1 and F2 generation?

(ii)Give the phenotypic ratio of F2 generation.

(iii)List the generalizations of Mendel that can be derived from the above cross.

Ans: Hint: work out like question No.45

Phenotype of F1 generation-all axial violet flowers

Genotype of F1 generation –AaVv

(ii)Phenotypic ratio of F2 generation 9:3:3:1

(iii)Law of independent assortment

70. A true breeding pea plant homozygous for inflated green pods is crossed with another pea

plant with constricted yellow pods (ffgg).

(i)What would be the phenotype and genotype of F1 and F2 generation? (ii)Give the phenotypic ratio of F2 generation.

(iii)List the generalizations of Mendel that can be derived from the above cross.

Ans: Hint: Answer in the lines of question No.46

47 (i) How does a Chromosomal disorder differ from a Mendelian disorder? (ii) Name any two chromosomal aberration associated disorders. (iii) List the characteristics of the disorders mentioned above that help in their diagnosis

Mendelian Disorder

Chromosomal Disorder

(i) This disorder is mainly due to alteration or mutation in the single gene.

This disorder is caused due to absence or excess or abnormal arrangement of one or more chromosomes

(ii) This follows Mendel’s principles of inheritance

This does not follow Mendel’s principles of inheritance

(iii) This may be recessive or dominant in nature

This is always dominant in nature.

(iv) For example, haemophilia, sickle-cell anaemia

For example, Turner’s syndrome

(ii) Two chromosomal aberration-associated disorders are Down’s syndrome and Klinefelter’s syndrome. (iii) (a) Down’s syndrome: The individuals have overall masculine development but they

express feminine development like development of breast, i.e., gynaecomastia. They are

sterile. This is caused by trisomy of 21st chromosome.

(b) Klinefelter’s syndrome: The females are sterile as ovaries are rudimentary. Other

secondary sexual characters are also lacking. This caused by XXY karyotype.

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