ABO Blood Group Inheritance via Punnett Square

Steps:

• Father AB has genotype I^A I^B, contributing I^A or I^B allele equally.
• Mother O has genotype I^O I^O, contributing only I^O allele.
• Possible offspring genotypes: I^A I^O (blood type A) or I^B I^O (blood type B).
• Each combination occurs with 50% probability, yielding 1:1 ratio of A:B.

Why A is correct:

• Codominance in ABO system means I^A or I^B with I^O expresses as A or B phenotype, per Mendelian segregation.

Why the others are wrong:

• B, C, D all predict O blood type, but no I^O I^O genotype possible since father always contributes I^A or I^B.

Final answer: A