Genetics – Sex Determination: NEET MCQs with Answers

15 free questions on Genetics – Sex Determination for NEET (UG), starting with previous-year NEET and AIPMT questions. Try each one, then tap Show answer for the answer and a short explanation.

Syllabus covered: Sex Determination: Sex determination-In humans, birds, honey bee;

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Question 1

Previous-year question
Select the incorrect statement. [NEET 2019]
  1. The male fruit fly is heterogametic
  2. In male grasshoppers, 50% of the sperms have no sex chromosome
  3. In domesticated fowls, the sex of the progeny depends on the type of sperm rather than the egg
  4. In humans, all ova carry an X chromosome
Show answer
Answer: (C) In domesticated fowls, the sex of the progeny depends on the type of sperm rather than the egg
Explanation: Fowls follow the ZZ-ZW system in which the female is heterogametic. The sex of the chick therefore depends on whether the egg carries a Z or a W chromosome, not on the type of sperm.  

Question 2

Previous-year question
A family of five daughters only is expecting sixth issue. The chance of its being a son is [AIPMT 1988]
  1. Zero
  2. 25%
  3. 50%
  4. 100%
Show answer
Answer: (C) 50%
Explanation: Each conception is an independent event, so the sex of previous children does not affect later ones. Since the male produces X- and Y-bearing sperms in equal numbers, the chance of a son at the sixth birth remains 50%.

Question 3

Previous-year question
Diploid chromosome number in humans is [AIPMT 1989]
  1. 46
  2. 44
  3. 48
  4. 42
Show answer
Answer: (A) 46
Explanation: Human beings have 23 pairs of chromosomes, of which 22 pairs are autosomes and one pair is the sex chromosomes. The total diploid number is therefore 23 × 2 = 46.

Question 4

Previous-year question
Sex is determined in human beings [AIPMT 1993]
  1. by ovum
  2. at the time of fertilisation
  3. 40 days after fertilisation
  4. seventh to eight week when genitals differentiate in foetus
Show answer
Answer: (B) at the time of fertilisation
Explanation: Sex in human beings is determined at fertilisation, because it depends on which type of sperm fertilises the ovum. The male produces X-bearing and Y-bearing sperms in equal numbers, while all ova carry X.

Question 5

Previous-year question
Mr. Kapoor has Bb autosomal gene pair and d allele sex-linked. What shall be proportional of Bd in sperms? [AIPMT 1993]
  1. Zero
  2. 1/2
  3. 1/4
  4. 1/8
Show answer
Answer: (C) 1/4
Explanation: Half of the sperms will carry B from the Bb pair, and half will carry the X chromosome bearing d. Since the two genes assort independently, the proportion of Bd sperms is 1/2 × 1/2 = 1/4.

Question 6

Previous-year question
Genes located on Y-chromosome are [AIPMT 1994]
  1. mutant genes
  2. sex-linked genes
  3. autosomal genes
  4. holandric genes
Show answer
Answer: (D) holandric genes
Explanation: Holandric genes are those that occur on the Y-chromosome. Since they are never expressed in females, they are transmitted directly from father to son, e.g. hairy ears (hypertrichosis) in man.

Question 7

Previous-year question
When an animal has both the characters of male and female, it is called [AIPMT 1996]
  1. super female
  2. super male
  3. intersex
  4. gynandromorph
Show answer
Answer: (D) gynandromorph
Explanation: A gynandromorph (hermaphrodite in the loose sense) is an animal that possesses both male and female characteristics, for example the earthworm. Individuals of many invertebrate groups are hermaphrodites.
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Question 8

Previous-year question
Genetic identity of a human male is determined by [AIPMT 1997]
  1. autosome
  2. nucleolus
  3. sex chromosome
  4. cell organelles
Show answer
Answer: (C) sex chromosome
Explanation: The genetic identity of a human male is determined by the sex chromosomes. Sex is fixed at fertilisation: if an X-bearing sperm fertilises the ovum the child is female, and if a Y-bearing sperm does so the child is male.

Question 9

Previous-year question
Foetal sex can be determined by examining cells from the amniotic fluid by looking for [AIPMT 1997]
  1. Barr bodies
  2. autosomes
  3. chiasmata
  4. kinetochore
Show answer
Answer: (A) Barr bodies
Explanation: Amniotic fluid contains living cells shed from the skin of the foetus. In non-dividing nuclei one X chromosome remains active while an additional X, if present, appears as a darkly staining Barr body — its presence indicates a female foetus.

Question 10

Previous-year question
Drosophila flies with XXY genotype are females, but human beings with such genotype are abnormal males. It shows that [AIPMT 2000]
  1. Y-chromosome is essential for sex determination in Drosophila
  2. Y-chromosome is female determining in Drosophila
  3. Y-chromosome is male determining in human beings
  4. Y-chromosome has no role in sex determination either in Drosophila or in human beings
Show answer
Answer: (C) Y-chromosome is male determining in human beings
Explanation: In human beings the presence of a Y chromosome is required for male development, so even XXY individuals are male (Klinefelter's syndrome). In Drosophila sex depends on the X : autosome ratio and the Y plays no significant role, so XXY flies are female.

Question 11

Previous-year question
Probability of four sons of a couple is [AIPMT 2001]
  1. 1/4
  2. 1/8
  3. 1/16
  4. 1/32
Show answer
Answer: (C) 1/16
Explanation: The probability of a son at each birth is 1/2 and each birth is an independent event. Therefore the probability of four sons in succession is 1/2 × 1/2 × 1/2 × 1/2 = 1/16.

Question 12

Previous-year question
Male XX and female XY sometime occur due to [AIPMT 2001]
  1. deletion
  2. transfer of segments in X and Y-chromosome
  3. aneuploidy
  4. hormonal imbalance
Show answer
Answer: (B) transfer of segments in X and Y-chromosome
Explanation: XX males and XY females occasionally arise through the transfer of chromosome segments between the X and Y chromosomes, so that the male-determining region ends up on the 'wrong' chromosome.

Question 13

Previous-year question
Number of Barr bodies in XXXX female is [AIPMT 2001]
  1. 1
  2. 2
  3. 3
  4. 4
Show answer
Answer: (C) 3
Explanation: A Barr body is a mass of condensed sex chromatin formed from an inactivated X chromosome. Whenever there is more than one X, the number of Barr bodies is one less than the number of X chromosomes; hence an XXXX female has three Barr bodies.

Question 14

Previous-year question
Pattern baldness, moustaches and beard in human males are examples of [AIPMT 2003]
  1. sex differentiating traits
  2. sex determining traits
  3. sex linked traits
  4. sex limited traits
Show answer
Answer: (D) sex limited traits
Explanation: Sex-limited traits are those expressed in one sex only. Moustaches and beard are found only in human males, and statistical analysis suggests that premature baldness is controlled by a gene expressed only in the presence of a certain level of androgen.

Question 15

Previous-year question
In Drosophila, the sex is determined by [AIPMT 2003]
  1. the ratio of pairs of X-chromosomes to the pairs of autosomes
  2. whether the egg is fertilised or develops parthenogenetically
  3. the ratio of number of X-chromosomes to the set of autosomes
  4. X and Y-chromosomes
Show answer
Answer: (C) the ratio of number of X-chromosomes to the set of autosomes
Explanation: Calvin Bridges demonstrated that in Drosophila sex is determined by the ratio of the number of X chromosomes to the sets of autosomes. According to this genic balance theory the Y chromosome plays no significant role in determining sex.

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