Principles of Inheritance & Variation — NEET PYQ
20 previous year questions on Principles of Inheritance & Variation for NEET Biology. Filter by year, solve each MCQ, and review detailed solutions.
Principles of Inheritance & Variation in NEET — Weightage & What Actually Gets Asked
Principles of Inheritance & Variation (NCERT Class 12 Biology, "Genetics & Evolution" unit) is one of the highest-return chapters in all of NEET Biology. The single chapter is asked roughly 3–4 questions almost every year, and together with Molecular Basis of Inheritance and Evolution the Genetics unit is usually the single highest-weight block of the whole paper. The good news for PYQ practice: the ideas repeat — Mendelian ratios, sex-linked disorders and chromosomal syndromes come back year after year in new wording.
| NEET question frequency | ~3–4 questions from this chapter most years |
| Genetics unit weightage | ~9–10 Qs (with Molecular Basis + Evolution) — among the highest of any unit |
| NCERT source | Class 12, Ch. "Principles of Inheritance & Variation" |
| Difficulty trend | Easy–Moderate, shifting toward match-the-column & multi-statement application |
High-Yield Sub-Topics (most-asked first)
- Mendelian ratios & the test cross. Monohybrid 3:1 (genotypic 1:2:1), dihybrid 9:3:3:1, and the test cross (a dominant phenotype × homozygous recessive) used to expose an unknown genotype. The most-asked single theme — practise reading a ratio backwards to the parent genotypes, not just forwards.
- Deviations from Mendelism. Incomplete dominance (snapdragon — F₂ phenotype ratio equals the genotype ratio, 1:2:1), codominance (ABO "AB" blood group expresses BOTH antigens), multiple alleles (Iᴬ, Iᴮ, i give six genotypes), and pleiotropy (one gene, many traits — sickle cell, PKU). NEET tests these distinctions almost every year.
- Sex determination systems. XX–XY (humans, Drosophila), XX–XO (grasshopper), ZZ–ZW (birds), and the haplodiploid honeybee system (males are haploid, developing from unfertilised eggs). In humans the sperm decides sex, and the SRY gene on the Y triggers male development.
- Sex-linked & Mendelian disorders. Haemophilia and red–green colour blindness are X-linked recessive (commoner in males; a carrier mother passes it to ~50% of sons). Sickle-cell anaemia = point mutation (Glu→Val at the 6th position of the β-globin chain, autosomal recessive); thalassemia = reduced globin synthesis; PKU = phenylalanine hydroxylase deficiency. Pedigree-reading questions hang on these.
- Chromosomal disorders (karyotypes). Down syndrome = trisomy 21 (47,+21); Turner = 45,X (the only viable monosomy, female); Klinefelter = 47,XXY (male). The exact karyotype is an almost-guaranteed single-fact mark — lock all three.
Common Mistakes Students Make
- Confusing incomplete dominance with codominance. Incomplete dominance BLENDS to an intermediate (pink); codominance shows both alleles fully and separately (AB blood = A and B antigens both present).
- Swapping Turner (45,X — female, monosomy) and Klinefelter (47,XXY — male, extra X). A whole mark can turn on this one character.
- Saying crossing over happens between sister chromatids — it is between NON-sister chromatids of homologous chromosomes, in the pachytene stage of prophase I.
- Forgetting that linked genes do NOT assort independently, so a dihybrid cross of linked genes does not give 9:3:3:1 — recombination frequency between them measures map distance.
Frequently Asked Questions
How many questions come from Principles of Inheritance and Variation in NEET?
Typically 3–4 questions from this chapter alone, almost every year. Counting the whole Genetics & Evolution unit (this chapter plus Molecular Basis of Inheritance and Evolution), it is usually among the highest-weight units in the paper at roughly 9–10 questions — which is why genetics is non-negotiable for a top NEET rank.
Is genetics hard for NEET?
It is conceptual rather than memory-heavy, so it feels hard only until the logic clicks. Once you can read a cross both ways (parents → ratio and ratio → parents) and you have the karyotypes and X-linked patterns memorised, it becomes one of the most reliable scoring chapters because the question types repeat.
What are the most important topics in Principles of Inheritance for NEET?
In priority order: Mendelian ratios and the test cross, deviations from Mendelism (incomplete/codominance, multiple alleles, pleiotropy), sex-determination systems, X-linked disorders with pedigree analysis, and the three chromosomal syndromes (Down, Turner, Klinefelter) with their exact karyotypes.
How should I use previous year questions for genetics?
Drill them by theme, not by year. Because NEET re-asks the same handful of ideas, sorting PYQs into ratios / deviations / sex-linkage / disorders and solving each cluster together makes the repeating patterns obvious and exposes the exact distinctions (e.g. Turner vs Klinefelter) the examiners keep testing.
More Chapters in Genetics & Evolution
Need Help with Principles of Inheritance & Variation?
Get 1-on-1 doubt sessions and personalised PYQ analysis with our NEET Biology coaching mentors.