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NEET Principles of Inheritance and Variation: 5 practice MCQs

By the PrepMatic team · Updated 9 Oct 2026 · 4 min read

Principles of Inheritance and Variation is the first genetics chapter in Class 12 Biology, and it is the one with calculations: ratios, probabilities and pedigrees. The five MCQs below cover the F2 genotypic ratio of a monohybrid cross, a dihybrid fraction, ABO inheritance, sex-linked colour blindness and a chromosomal disorder.

What this chapter covers in the NEET syllabus

The NMC unit is Genetics and Evolution, and this chapter is its inheritance half, taught as the Class 12 NCERT chapter of the same name. The topics are:

• Mendel's laws of inheritance: dominance, segregation and independent assortment, and the test cross.
• Incomplete dominance, codominance, multiple alleles (ABO blood groups) and pleiotropy.
• Polygenic inheritance.
• Chromosomal theory of inheritance, linkage and recombination.
• Sex determination in humans, birds and honey bees.
• Mutation, pedigree analysis, and genetic disorders: Mendelian (haemophilia, colour blindness, sickle-cell anaemia, thalassemia, phenylketonuria) and chromosomal (Down's, Klinefelter's and Turner's syndromes).

Five practice MCQs on Principles of Inheritance

Question 1

In a monohybrid cross between two heterozygous (Tt × Tt) plants, the genotypic ratio in the F2 generation is:

• A. 3 : 1
• B. 1 : 2 : 1
• C. 1 : 1
• D. 9 : 3 : 3 : 1

Question 2

In a dihybrid cross between RRYY (round, yellow) and rryy (wrinkled, green) pea plants, the fraction of F2 plants that are round and yellow is:

• A. 3/16
• B. 1/16
• C. 1/4
• D. 9/16

Question 3

A woman with blood group AB marries a man with blood group O. Their children can have blood group:

• A. A or B only
• B. A, B, AB or O
• C. AB or O only
• D. O only

Question 4

A woman who is a carrier for colour blindness marries a man with normal vision. The chance that a son is colour-blind is:

• A. 0%
• B. 25%
• C. 50%
• D. 100%

Question 5

The chromosome complement of a person with Turner's syndrome is:

• A. 44 autosomes + XXY
• B. 44 autosomes + XYY
• C. 45 autosomes + XX
• D. 44 autosomes + X (one sex chromosome)

Answers and explanations

1. B. Selfing Tt gives TT, Tt and tt in the ratio 1 : 2 : 1, which is the genotypic ratio. The phenotypic ratio is 3 : 1 when T is completely dominant. Option D is the dihybrid phenotypic ratio.
2. D. In the F2 of a dihybrid cross the phenotypes are in the ratio 9 round yellow : 3 round green : 3 wrinkled yellow : 1 wrinkled green. So 9/16 are round and yellow.
3. A. Blood group AB is I^A I^B and group O is ii. The children can only be I^A i (group A) or I^B i (group B). Neither AB nor O is possible, which is a standard question on exclusion of parentage.
4. C. The mother is X^c X (a carrier, with X^c the colour-blind allele) and the father is XY (normal). Each son receives his mother's X, which is X^c half of the time, so 50% of sons are colour-blind. All daughters have normal vision, though half of them will be carriers.
5. D. Turner's syndrome is a monosomy of the sex chromosomes, 45 chromosomes in all (44 autosomes + one X), written XO. The affected person is a sterile female with a short stature and underdeveloped ovaries. Klinefelter's syndrome is XXY.

How to prepare Principles of Inheritance

• Set up crosses the same way each time. Write parental genotypes, gametes, then a Punnett square. For two genes, multiply separate single-gene ratios (the product rule) instead of drawing a 16-box square. Practise ten dihybrid problems and ten test-cross problems.
• Know every ratio and its cause. 3 : 1, 1 : 2 : 1, 9 : 3 : 3 : 1, 1 : 1 test cross, 1 : 2 : 1 for incomplete dominance and codominance, and what changes in each. Questions often give a ratio and ask you to identify the type of inheritance.
• Master ABO blood groups as multiple alleles. Three alleles (I^A, I^B, i), six genotypes and four phenotypes, with codominance of I^A and I^B.
• Treat sex-linked inheritance carefully. Write the genotypes with the X chromosome explicitly (X^c X, X^c Y). Pedigree questions need you to identify whether a trait is autosomal or sex-linked, dominant or recessive.
• Make a disorders table: disorder, cause (gene or chromosome), pattern of inheritance, and symptoms. Include the karyotype of each chromosomal disorder.

Genetics rewards practice more than reading, so solve five problems daily. The NEET genetics and evolution guide goes deeper on problem types and common mistakes, and the NEET Biology preparation guide places this chapter in the plan.

Take a full Principles of Inheritance test on PrepMatic

Genetics problems need steady practice. PrepMatic's analytics track your accuracy over time and your speed per question as you take more tests, and each topic test is about 15 questions in 30 minutes with NEET's negative marking. Topic tests are in the free Basic plan, and the practice hub has more chapters.

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