Question

A woman who has blood type A positive has a daughter who is type O positive and a son who is type B negative. Rh positive is a trait that shows simple dominance over Rh negative and is designated by the alleles R and r, respectively. A third gene for the MN blood group has codominant alleles M and N.
Which of the following is a possible partial genotype for the son?
A) IBIB
B) IBIA
C) ii
D) IBi
E) IAIA

Answer 1

The answer is D) IBi

A mother has either AA or AO genotype. Since her daughter has OO genotype, the one O allele is from a father and one is from the mother.  Thus, mother must have allele O. So mother's genotype is AO.

A mother with AO genotype will pass to her son either A or O allele. Since son is type B negative, it could inherit from mother only O allele. Son's genotype is BO. This means that he inherited from the father B allele.

Talking of Rh, her son is type B negative. A negative Rh phenotype contains both recessive alleles r.
Therefore, the son genotype is BOrr. In terms of the alleles for the I locus, it can be represented as $I^{B}$i.