NEET Genetics: Hardy-Weinberg and Linkage
NEET-UG Biology Genetics questions test conceptual understanding of Mendelian and non-Mendelian inheritance, and numerical application of the Hardy-Weinberg principle. NEET awards +4 for correct and −1 for incorrect (Biology = 90 questions, 360 marks).
Hardy-Weinberg principle: in a large, randomly mating population with no mutation, migration, natural selection, or genetic drift, allele frequencies remain constant. If frequency of allele A = p and a = q, then p + q = 1. Genotype frequencies at equilibrium: AA = p², Aa = 2pq, aa = q². Application: if 9% of population is homozygous recessive (aa), then q² = 0.09, q = 0.3, p = 0.7. Frequency of heterozygotes Aa = 2pq = 2(0.7)(0.3) = 0.42 = 42%.
Linkage and recombination: linked genes are on the same chromosome and violate Mendel's law of independent assortment. Recombination frequency (cM) = (recombinant progeny / total progeny) × 100%. Used to construct genetic maps. NEET tests: identifying linked vs unlinked from cross data (expected 9:3:3:1 for unlinked; deviation indicates linkage or epistasis); calculating recombination frequency from testcross data.
Sex-linked inheritance: X-linked recessive conditions (haemophilia, colour blindness) appear more frequently in males (XY — one copy sufficient for expression) than females (XX — need two recessive alleles). Carrier female: X^A X^a — phenotypically normal, 50% of sons affected. NEET pedigree questions: identify mode of inheritance (autosomal/sex-linked, dominant/recessive) and predict offspring ratios.