NEET (UG) · Botany, Class 12
Principles of Inheritance and Variation: NEET PYQ, 2018–2026
Principles of Inheritance and Variation (Botany, Class 12) has been asked 28 times in the 7 NEET papers from 2018, 2020, 2021, 2023, 2024, 2025 and 2026: about 4 questions a paper, 8% of all Botany questions. It is the 3rd most-asked of 17 Botany chapters. NEET 2026 had 3 from it. Last checked 28 October 2026.
Questions per paper
Year by year.
| Year | Questions |
|---|---|
| 2018 | 4 |
| 2020 | 4 |
| 2021 | 3 |
| 2023 | 5 |
| 2024 | 6 |
| 2025 | 3 |
| 2026 | 3 |
From 2021 to 2024 each paper had 200 questions (a Section B with a choice); the others had 180.
Inside the chapter
Topics asked most.
- Genetic disorders10
- Deviations from Mendelism8
- Mendelian genetics8
- Linkage and recombination2
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10 Principles of Inheritance and Variation questions to practise.
Our own questions, written in the NEET pattern and checked, each with an explanation. Pick an option to see the answer.
Q1 · Botany · Principles of Inheritance and Variation
Morgan found that when the two genes of a dihybrid cross are situated on the same chromosome, the F₂ generation shows:
Answer: (A)
Morgan saw that when two genes lie on the same chromosome, the proportion of parental gene combinations is much higher than that of the non-parental type. He attributed this to the physical association, or linkage, of the two genes, and used the term recombination for the generation of non-parental gene combinations.
Q2 · Botany · Principles of Inheritance and Variation
In β-thalassaemia, the anaemia results from which molecular defect?
Answer: (A)
β-thalassaemia is an autosomal recessive single-gene disorder. Mutations in the HBB gene reduce or abolish β-globin synthesis. Haemoglobin needs equal α and β chains, so the excess α-chains form insoluble aggregates that damage red blood cell precursors. The result is haemolytic anaemia. Distinguish it from sickle-cell anaemia, where the β-chain is structurally altered rather than underproduced.
Q3 · Botany · Principles of Inheritance and Variation
In a testcross, a female heterozygous for three linked genes in the order A-B-C (genotype ABC/abc) is crossed with an abc/abc male. Of 1000 progeny, 430 are ABC, 430 are abc, 50 are Abc, 50 are aBC, 10 are ABc, 10 are abC, 10 are AbC and 10 are aBc. What is the map distance between genes A and C?
Answer: (C)
Identify parental classes (ABC, abc), single crossover classes for A-B (Abc, aBC), single crossover classes for B-C (ABc, abC) and double crossover classes (AbC, aBc), which are the rarest and have B switched relative to the flanking genes. A-B recombinants = 100 + 20 = 120, so 12 cM. B-C recombinants = 20 + 20 = 40, so 4 cM. Observed A-C recombinants are 120 because double crossovers return A and C to parental arrangement, so the observed value (12) underestimates the true distance. The true A-C distance is 12 + 4 = 16 cM.
Q4 · Botany · Principles of Inheritance and Variation
Which set of features is characteristic of Down's syndrome?
Answer: (A)
Principle: Down's syndrome is a trisomy of chromosome 21 (2n+1). Its clinical features include mental retardation, a flattened face, and a single palmar crease. Application: when a question names these features, identify the autosomal trisomy rather than a sex-chromosome disorder.
Q5 · Botany · Principles of Inheritance and Variation
Hypertrichosis of the pinna (excess hair on the outer ear) is a trait that is passed only from father to son. What is the most accurate reason for this inheritance pattern?
Answer: (A)
Principle: genes on the Y chromosome are inherited only through males, from father to all sons, because the Y is passed from father to son only. Apply it: a trait restricted to males and passed from fathers to all sons, with no transmission to daughters, is Y-linked. Compare X-linked traits, which go from mother to son and from father to daughter.
Q6 · Botany · Principles of Inheritance and Variation
Which statement about a drone (male honey bee) is correct?
Answer: (B)
In the honey bee an unfertilised egg develops into a male by parthenogenesis, so the drone is haploid with 16 chromosomes, while the diploid females have 32. Being haploid, the males produce sperms by mitosis. A drone therefore has no father and cannot have sons, though it has a grandfather and can have grandsons.
Q7 · Botany · Principles of Inheritance and Variation
A heterozygote with two linked genes in coupling is test-crossed with a homozygous recessive individual, and the genes show complete linkage with no crossing over. What phenotypic pattern will the progeny show?
Answer: (A)
In a test cross, the heterozygote contributes its gametes and the homozygous recessive parent contributes only recessive alleles, so progeny phenotypes reflect the gametes produced by the heterozygote. With complete linkage, the heterozygote makes only parental gametes, so only two phenotypes appear, in a 1:1 ratio.
Q8 · Botany · Principles of Inheritance and Variation
In the ABO system, a person of genotype I^A I^B hh has a blood group that is not A, B or AB. Which blood group does this person show?
Answer: (A)
ABO is a multiple-allele, codominant system, but its antigens are built on a precursor substance made under the control of the H gene. The hh genotype cannot make the precursor, so the I^A and I^B alleles have no substrate to act on. The person therefore expresses the O phenotype, the Bombay phenotype, regardless of the ABO genotype.
Q9 · Botany · Principles of Inheritance and Variation
A couple plans to have four children. Assuming each birth is independent and the chance of a boy or girl is equal at 1/2, what is the probability that exactly two of the four children are girls?
Answer: (A)
Each child's sex is an independent Bernoulli trial with p = 1/2. The probability of exactly k successes in n trials is C(n,k) p^k (1-p)^(n-k). Here n = 4, k = 2, so C(4,2)(1/2)^2(1/2)^2 = 6 × 1/16 = 3/8. The binomial coefficient is the factor students most often omit.
Q10 · Botany · Principles of Inheritance and Variation
Which feature of the garden pea (Pisum sativum) made it especially convenient for Mendel to obtain true-breeding lines?
Answer: (A)
Mendel needed parents that breed true for each trait so that crosses gave clearly defined results. The pea is normally self-pollinated inside a closed flower, so each variety stays pure across generations. Recall this under Mendel's experimental material in NCERT Class 12 Chapter 5.
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About Principles of Inheritance and Variation in NEET.
How many questions come from Principles of Inheritance and Variation in NEET?
Principles of Inheritance and Variation (Botany, Class 12) has been asked 28 times in the 7 NEET papers from 2018, 2020, 2021, 2023, 2024, 2025 and 2026: about 4 questions a paper, 8% of all Botany questions. It is the 3rd most-asked of 17 Botany chapters. NEET 2026 had 3 from it.
Which topics of Principles of Inheritance and Variation are asked most in NEET?
Genetic disorders (10), Deviations from Mendelism (8), Mendelian genetics (8), Linkage and recombination (2), counted over the papers from 2018–2026.
Is Principles of Inheritance and Variation important for NEET 2027?
It is in the syllabus in force, so it can be asked. By past papers it ranks 3 of 17 in Botany; use that to decide how much time it gets, not whether to study it.
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