If a boy has blood type O and his mother has blood type A,what is the genotype of his father?

Analyze the question

The boy has blood group O, so his genotype must be OO. He got one O allele from each parent. His mother is group A, so she must be AO (heterozygous). That means the father must also carry at least one O allele.

Concept: ABO blood group inheritance

• Alleles: I^A and I^B are codominant, and O (i) is recessive.
• Group A: AA or AO
• Group B: BB or BO
• Group AB: AB
• Group O: OO

A child with group O must receive an O allele from both parents.

Check the options

• A. BB: has no O allele, so it cannot produce an O child. ✗
• B. AA: has no O allele. ✗
• C. AO: has one O allele, so it can pass on O. ✓
• D. AB: has no O allele. ✗

Cross (mother AO × father AO):

| | A | O | |---|---|---| | A | AA | AO | | O | AO | OO |

This gives a 25% chance of an OO child, so the boy's blood group is possible.

Option C is the only genotype listed that carries an O allele.

Tip: If a child is group O, both parents must carry an O allele. When you see an O child, look for the option that contains O.