Punnett square analysis of ABO alleles

Steps:

• Identify genotypes: Homozygous group A woman is I^A I^A; heterozygous group B man is I^B i.
• Determine gametes: Woman produces only I^A eggs; man produces I^B or i sperm (50% each).
• Combine alleles: Offspring genotypes are I^A I^B (AB blood type) or I^A i (A blood type).
• Conclude phenotypes: Possible blood groups are A and AB only.

Why B is correct:

• ABO inheritance follows codominance and recessiveness, where I^A and I^B produce A and AB phenotypes when paired, excluding B or O without i from both parents.

Why the others are wrong:

• A excludes AB, but I^A I^B offspring occur from father's I^B allele.
• C excludes A, but I^A i offspring occur from father's i allele.
• D includes B, but no I^B i offspring possible without mother's i allele.

Final answer: B