Question

This question refers to the ABO blood type locus. Remember that the A and B alleles are codominant to each other and both are dominant to the O allele. Assume no epistatic interactions with the H locus. A woman is blood type AB. Her child is blood type B. She wants to get child support from a man who is blood type A. Can this man be the father of the woman's child based on these data?

Yes
No

Answer 1

Answer:

No

Explanation:

If the mother has a phenotype AB, she only can have the genotype $I^{A}I^{B}$. This because A and B are codominant alleles.  The child is blood type A, so he can be heterozygote or homozygote for allele B.  The possible father is blood type A and he can be heterozygote or homozygote for allele A.  Hence, possibles genotypes are:

Mother: $I^{A}I^{B}$

Child:  $I^{B}I^{B}$ or $I^{B}I^{o}$

Possible father: $I^{A}I^{A}$ or $I^{A}I^{o}$

If the father is  $I^{A}I^{A}$, children of these parents can have the genotypes shown in the first Punnet Square.

And, if the father is  $I^{A}I^{o}$, possible progeny will be the one on the second Punnet Square.

So, it is impossible for this couple to have a son blood type A.