The 8 Most Dangerous NEET Traps in Mendelian Genetics

Trap 1 — Reversed phenotypic/genotypic ratios: Phenotypic ratio of monohybrid F2 = 3:1 (not 1:2:1). Genotypic = 1:2:1. The 1:2:1 ratio applies to phenotypes ONLY in incomplete or co-dominance.

Trap 2 — Yellow vs Green dominance: Yellow seed colour is dominant; but Yellow pod colour is RECESSIVE (Green pod is dominant). These are opposite — study as a matched pair, not a rule.

Trap 3 — Calling AB blood group "incomplete dominance": AB blood group is CO-DOMINANCE. Blending is incomplete dominance. Simultaneous full expression of both alleles is co-dominance. Pink snapdragon ≠ AB blood group.

Trap 4 — Pleiotropy vs Polygenic reversal: Pleiotropy = one gene, many effects. Polygenic = many genes, one trait. These are definitions frequently reversed in NEET options; read the definition carefully.

Trap 5 — AB × O producing O or AB offspring: AB parent ($I^A$ $I^B$) contributes only $I^A$ or $I^B$ gametes. O parent (ii) contributes only i. Children = groups A and B only. O and AB children are impossible.

Trap 6 — Applying 9:3:3:1 to linked genes: This ratio only applies when genes are on different chromosomes. Linked genes produce parental-class-heavy ratios with fewer recombinants.

Trap 7 — Recombination frequency above 50%: Maximum observable recombination frequency is 50%. No pair of genes on the same chromosome can show more than 50% recombinants, because multiple crossovers restore parental combinations.

Trap 8 — Multiple alleles means one person has 3 alleles: Multiple allelism is a population-level phenomenon. Each diploid individual still carries exactly two alleles. Three alleles ($I^A$, $I^B$, i) exist across the human population, not within one person.