In a monohybrid cross between two heterozygous garden pea plants (Tt x Tt) where tallness (T) is completely dominant to dwarfness (t), what is the theoretical probability of obtaining an offspring that is dwarf?
Answer and explanation
Correct answer: C. 25% (1 in 4)
- Step 1: Construct a Punnett square for cross Tt x Tt: Gametes T and t from each parent.
- Step 2: Offspring genotypic distribution: 1 TT, 2 Tt, 1 tt.
- Step 3: Dwarf phenotype requires the homozygous recessive genotype (tt).
- Step 4: Determine probability: 1 out of 4 combinations = 25%.
Answer
25% (1 in 4).
Why not the others: '50% (1 in 2)' is the proportion of heterozygous carriers (Tt); '75% (3 in 4)' is the probability of the dominant tall phenotype; '0%' occurs only when at least one parent is homozygous dominant (TT).
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