NEET Biology Principles of Inheritance and Variation MCQs Set 13

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Multiple Choice Questions

Question 1: A man and a woman, who do not show any apparent signs of a certain inherited disease, have seven children (2 daughters and 5 sons). Three of the sons suffer from the given disease but none of the daughters are affected. Which of the following mode of inheritance do you suggest for this disease?
(a) Autosomal dominant
(b) Sex-linked dominant
(c) Sex-limited recessive
(d) Sex-linked recessive
Show Answer & Explanation

Answer: (d) Sex-linked recessive

Explanation:
1. Unaffected parents with affected sons only indicate an X-linked recessive disease.

Teacher's Note:
1. Mother is a carrier.

Question 2: At a particular locus, frequency of ‘A’ allele is 0.6 and that of ‘a’ is 0.4. What would be the frequency of heterozygotes in a random mating population at equilibrium?
(a) 0.16
(b) 0.48
(c) 0.36
(d) 0.24
Show Answer & Explanation

Answer: (b) 0.48

Explanation:
1. Heterozygotes frequency = 2pq = 2 x 0.6 x 0.4 = 0.48.

Teacher's Note:
1. Hardy-Weinberg.

Question 3: A woman with normal vision, but whose father was colour blind, marries a colourblind man. Suppose that the fourth child of this couple was a boy. This boy:
(a) Must have normal colour vision
(b) Will be partially colourblind since he is heterozygous for the colourblind mutant allele
(c) Must be colourblind
(d) May be colourblind or may be of normal vision
Show Answer & Explanation

Answer: (d) May be colourblind or may be of normal vision

Explanation:
1. The mother is a carrier (XCX) and the father colour blind (XCY); a son may be colour blind (XCY) or normal (XY), each with 50% chance.

Teacher's Note:
1. Each child is an independent event.

Question 4: Haemophilia is more commonly seen in human males than in human females because
(a) This disease is due to an X-linked dominant mutation
(b) A greater proportion of girls die in infancy
(c) This disease is due to an X-linked recessive mutation
(d) This disease is due to a Y-linked recessive mutation
Show Answer & Explanation

Answer: (c) This disease is due to an X-linked recessive mutation

Explanation:
1. Haemophilia is X-linked recessive, so males with one X are affected more often.

Teacher's Note:
1. Hemizygous males.

Question 5: A woman with 47 chromosomes due to three copies of chromosome 21 is characterized by
(a) Down syndrome
(b) Triploidy
(c) Turner syndrome
(d) Super femaleness
Show Answer & Explanation

Answer: (a) Down syndrome

Explanation:
1. 47 chromosomes with three copies of chromosome 21 is Down syndrome.

Teacher's Note:
1. Trisomy 21.

Question 6: In order to find out the different types of gametes produced by a pea plant having the genotype AaBb, it should be crossed to a plant with the genotype
(a) aaBB
(b) AaBb
(c) AABB
(d) aabb
Show Answer & Explanation

Answer: (d) aabb

Explanation:
1. The gametes of AaBb are discovered by crossing it with aabb (test cross).

Teacher's Note:
1. aabb gives only ab gametes.

Question 7: Which of the following is not a hereditary disease?
(a) Cretinism
(b) Cystic fibrosis
(c) Thalassaemia
(d) Haemophilia
Show Answer & Explanation

Answer: (a) Cretinism

Explanation:
1. Cretinism is due to thyroxine deficiency (iodine deficiency) and is not hereditary, while cystic fibrosis, thalassaemia and haemophilia are hereditary.

Teacher's Note:
1. Hereditary means genetic.

Question 8: The salivary gland chromosomes in the dipteran larvae, are useful in gene mapping because
(a) These are much longer in size
(b) These are easy to stain
(c) These are fused
(d) They have endoreduplicated chromosomes
Show Answer & Explanation

Answer: (d) They have endoreduplicated chromosomes

Explanation:
1. Salivary gland chromosomes are giant because of endoreduplication (polyteny), which makes gene mapping easier.

Teacher's Note:
1. Polytene chromosomes show bands.

Question 9: Genetic variation in a population arises due to
(a) Mutations only
(b) Recombination only
(c) Mutations as well as recombination
(d) Reproductive isolation and selection
Show Answer & Explanation

Answer: (c) Mutations as well as recombination

Explanation:
1. Genetic variation arises by both mutations and recombination.

Teacher's Note:
1. Mutation creates new alleles; recombination shuffles them.

Question 10: Which one is the incorrect statement with regards to the importance of pedigree analysis?
(a) It helps to trace the inheritance of a specific trait
(b) It confirms that DNA is the carrier of genetic information
(c) It helps to understand whether the trait in question is dominant or recessive
(d) It confirms that the trait is linked to one of the autosome
Show Answer & Explanation

Answer: (b) It confirms that DNA is the carrier of genetic information

Explanation:
1. Pedigree analysis traces inheritance and tells whether a trait is dominant/recessive, autosomal/sex-linked; it cannot confirm that DNA is genetic material.

Teacher's Note:
1. DNA was proved by other experiments.

Question 11: In our society women are blamed for producing female children. Choose the correct answer for the sex- determination in humans
(a) Due to some defect in the women
(b) Due to some defect like aspermia in man
(c) Due to the genetic make up of the particular sperm which fertilizes the egg
(d) Due to the genetic make up of the egg
Show Answer & Explanation

Answer: (c) Due to the genetic make up of the particular sperm which fertilizes the egg

Explanation:
1. Sex of the child depends on the sperm (X or Y) that fertilises the egg, not the mother.

Teacher's Note:
1. Egg always carries X.

Question 12: Down’s syndrome in humans is due to
(a) Two ‘Y’ chromosomes
(b) Three ‘X’ chromosomes
(c) Three copies of chromosome 21
(d) Monosomy
Show Answer & Explanation

Answer: (c) Three copies of chromosome 21

Explanation:
1. Down syndrome is trisomy of chromosome 21.

Teacher's Note:
1. Three copies of chromosome 21.

Question 13: If two pea plants having red (dominant) coloured flowers with unknown genotypes are crossed, 75% of the flowers are red and 25% are white. The genotypic constitution of the parents having red coloured flowers will be
(a) Both homozygous
(b) One homozygous and other heterozygous
(c) Both heterozygous
(d) Both hemizygous
Show Answer & Explanation

Answer: (c) Both heterozygous

Explanation:
1. Red x red giving 3 red : 1 white means both parents are heterozygous (Rr x Rr).

Teacher's Note:
1. 3 : 1 ratio.

Question 14: Walter Sutton is famous for his contribution to
(a) Genetic engineering
(b) Totipotency
(c) Quantitative genetics
(d) Chromosomal theory of inheritance
Show Answer & Explanation

Answer: (d) Chromosomal theory of inheritance

Explanation:
1. Walter Sutton proposed the chromosomal theory of inheritance (with Boveri).

Teacher's Note:
1. Chromosomes carry genes.

Question 15: A polygenic trait is controlled by 3 genes A, B and C. In a cross AaBbCc × AaBbCc, the phenotypic ratio of the offsprings was observed as 1 : 6 : x : 20 : x : 6 : 1 What is the possible value of x?
(a) 3
(b) 9
(c) 15
(d) 25
Show Answer & Explanation

Answer: (c) 15

Explanation:
1. With three polygenes the ratio of F2 is 1 : 6 : 15 : 20 : 15 : 6 : 1, so x = 15.

Teacher's Note:
1. Binomial expansion of (a+b)^6.

Question 16: The chromosome constitution 2n – 2 of an organism represents
(a) Monosomic
(b) Nullisomic
(c) Haploid
(d) Trisomic
Show Answer & Explanation

Answer: (b) Nullisomic

Explanation:
1. 2n - 2 is the nullisomic condition (loss of both members of a pair).

Teacher's Note:
1. Monosomic = 2n - 1.

Question 17: Mendel's principle of segregation means that the germ cells always receive
(a) One pair of alleles
(b) One quarter of the genes
(c) One of the paired alleles
(d) Any pair of alleles
Show Answer & Explanation

Answer: (c) One of the paired alleles

Explanation:
1. By the principle of segregation, a gamete receives only one of the two alleles of a gene.

Teacher's Note:
1. Alleles separate during gamete formation.

Question 18: Absence of one sex chromosome causes
(a) Turner's syndrome
(b) Klinefelter's syndrome
(c) Down's syndrome
(d) Tay-Sach's syndrome
Show Answer & Explanation

Answer: (a) Turner's syndrome

Explanation:
1. Absence of one sex chromosome (XO) causes Turner's syndrome.

Teacher's Note:
1. Monosomy of X.

Question 19: The genes, which remain confined to differential region of Y-chromosome, are
(a) Autosomal genes
(b) Holandric genes
(c) Completely sex-linked genes
(d) Mutant genes
Show Answer & Explanation

Answer: (b) Holandric genes

Explanation:
1. Genes in the differential region of Y are Y-linked (holandric) genes.

Teacher's Note:
1. They pass from father to son.

Question 20: The colour blindness is more likely to occur in males than in females because
(a) The Y-chromosome of males have the genes for distinguishing colours
(b) Genes for characters are located on the X-chromosomes
(c) The trait is dominant in males and recessive in females
(d) None of these
Show Answer & Explanation

Answer: (b) Genes for characters are located on the X-chromosomes

Explanation:
1. Colour blindness genes are on the X chromosome, so males (XY) show the recessive trait with a single allele.

Teacher's Note:
1. Hemizygous condition.

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Practice MCQs for NEET Biology Principles of Inheritance and Variation

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