Small sample sizes mislead genetic conclusions

Steps:

• Man's blood group A means genotype IA IA (homozygous) or IA i (heterozygous); wife's O means ii (homozygous recessive).
• If man heterozygous, each child has 50% chance of A (IA i) or O (ii), so expected 1:1 ratio.
• Two A children possible by chance (probability 0.25), but doesn't rule out heterozygous father.
• Small family size (n=2) can't confirm ratios; larger samples needed for reliability.

Why B is correct:

• Mendel's law of segregation predicts ratios as probabilities over many offspring; small numbers follow binomial distribution, allowing deviations by chance.

Why the others are wrong:

• A: Blood group alleles are stable; mutations rare and irrelevant here.
• C: Group O is always ii, homozygous recessive—no heterozygosity possible.
• D: Heterozygous father (IA i) and O mother (ii) yield 1 A:1 O, not 3:1 (which requires different cross).

Final answer: B