NEET Previous Year Questions(PYQs) MCQs on Principles of Inheritance and Variation Class-XII Biology

Question 31 of 39

🟢 Re NEET 2026 📘 CLASS XII

Given below are two statements:

Statement I: Down's syndrome is caused by the absence of one of the X-chromosomes.

Statement II: Turner's syndrome is caused by the presence of an additional copy of the chromosomes.

In the light of the above statements, choose the correct answer from the options given below:

Down's syndrome is caused by trisomy of chromosome 21. Turner's syndrome is caused by the absence of one X chromosome, resulting in the chromosome complement 45, XO.

Question 32 of 39

🟢 Re NEET 2026 📘 CLASS XII

For a person with blood group 'O', which of the following is not a possible combination of parents' blood group genotypes?

A child with blood group O has genotype ii. Since the father (I^AI^B) has no i allele, this combination cannot produce an O blood group child.

Question 33 of 39

🟢 Re NEET 2026 📘 CLASS XII

Given below are two statements:

Assertion (A): In an experiment, Mendel observed that the F₁ progeny plants are all tall and none are dwarf.

Reason (R): Stem height is a contrasting trait, with tall being dominant and dwarf being recessive.

In the light of the above statements, choose the most appropriate answer from the options given below:

In Mendel's monohybrid cross, the dominant allele for tallness masks the recessive dwarf allele, so all F₁ plants are tall.

Question 34 of 39

🟢 NEET 2026 📘 CLASS XII

Which of the following statements are true with reference to the sex determination in honeybees?

(A) An offspring formed from the union of a sperm and an egg develops as a female (queen or worker).
(B) An unfertilized egg develops as a male by parthenogenesis.
(C) A male has half the number of chromosomes than that of a female.
(D) Males produce sperms by meiosis.
(E) Honeybees have a haplodiploid sex-determination system.

Choose the correct answer from the options given below:

Male honeybees are haploid and produce sperms by mitosis, not meiosis. Therefore statement D is incorrect.

Question 35 of 39

🟢 NEET 2026 📘 CLASS XII

Which one of the following disorders is caused by the substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the beta globin chain of the haemoglobin molecule?

Sickle-cell anaemia results from a point mutation in the β-globin gene causing substitution of glutamic acid by valine at the sixth position.

Question 36 of 39

🟢 NEET 2026 📘 CLASS XII

Match List-I with List-II:

List-I	List-II
A. Incomplete dominance	I. Human skin colour
B. Co-dominance	II. Inheritance of flower colour in Antirrhinum
C. Pleiotropy	III. Phenylketonuria disease in humans
D. Polygenic inheritance	IV. ABO blood groups

Incomplete dominance is seen in Antirrhinum, co-dominance in ABO blood groups, pleiotropy in phenylketonuria and polygenic inheritance in human skin colour.

Question 37 of 39

🟢 NEET 2026 📘 CLASS XII

What is the probability of having children with O blood group, where both mother and father are heterozygous for A and B blood groups, respectively?

Cross: I^Ai × I^Bi produces AB, A, B and O blood groups in the ratio 1:1:1:1. Therefore, O blood group has a probability of 25%.

Question 38 of 39

🟢 NEET 2026 📘 CLASS XII

In which animal do haploid cells divide mitotically to produce gametes?

Male honeybees are haploid. Since meiosis cannot occur in haploid individuals, sperms are produced by mitosis.

Question 39 of 39

🟢 NEET 2026 📘 CLASS XII

In a population of a grasshopper species, the chromosome number of some members is 23 and some other members possess 24 chromosomes. The 23 and 24 chromosome-bearing members in this species are ________.

Grasshoppers show the XO type of sex determination. Males possess 23 chromosomes (XO), whereas females possess 24 chromosomes (XX).

Principles of Inheritance and Variation NEET PYQs