Awoman 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 phenotype for the father?
a) a negative
b) o negative
c) b positive
d) ab negative
e) impossible to determine

The answer is C) B positive.

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.

Father has either BO or BB genotype. Since his daughter has OO genotype, she must inherit one O allele from the father. Thus, the father has BO genotype.

Talking of Rh, her son is type B negative. A negative Rh phenotype contains both recessive alleles r, so the mother must have allele r (she is either Rh+ heterozygous, or Rh- homozygous). The same is with father - he  is either Rh+ heterozygous, or Rh- homozygous.