Science (086) — AI-generated practice question

In F1 plants, the gene for tallness (T) comes from one parent and the gene for shortness (t) comes from the other, giving genotype Tt. Because a single copy of T is sufficient to produce a tall plant, T is dominant and t is recessive. The t allele is present but its effect is completely masked by T, so F1 plants appear tall.

During self-pollination of F1 (Tt × Tt), the two alleles separate and recombine randomly, producing offspring in the ratio TT : Tt : tt = 1 : 2 : 1. Only the tt plants (one-quarter) lack any T allele, so the recessive shortness trait is expressed again in F2.

Source: Chapter 8, Section 8.2.2

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• Key terms examiners expect: dominant, recessive, genotype (Tt, TT, tt), self-pollination, 1:2:1 ratio.
• The core idea is masking of recessive allele by dominant allele in heterozygous condition, and segregation during gamete formation restoring the recessive phenotype.
• Avoid vague phrases like "the gene disappeared" — always say it was present but not expressed.
• A Punnett square is not required for 3 marks but mentioning the 1:2:1 genotypic ratio earns credit.