Small sample size invalidates the man's genetic conclusion

Steps:

• Man has blood group A (genotype IAIA or IAi); wife has O (ii).
• If man is IAi, each child has 50% chance of A (IAi) and 50% O (ii).
• Both children A is possible outcome (probability 0.25 for n=2).
• Small family size (2 children) cannot reliably distinguish genotypes; larger sample needed for ratios.

Why A is correct:

• Mendelian ratios are expected probabilities, but small samples (n=2) often deviate due to chance, making conclusions from them unreliable.

Why the others are wrong:

• B: Blood group O requires homozygous recessive (ii) genotype; wife cannot carry dominant IA allele.
• C: Incorrect; heterozygous father (IAi) and O mother (ii) yield 1:1 A:O ratio, not 3:1.
• D: Same error as C; ratio is 1:1, not 3:1.

Final answer: A