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 phenotype for the father?
A) A negative
B) O negative
C) B positive
D) AB negative
E) impossible to determine

Answer 1

The father's possible phenotype, based on the blood types of his children and wife, could be B positive, as he must have both IB and Rh-positive alleles. So the correcct option is C.

Step-by-step explanation:

The question posed revolves around determining the possible phenotype of the father given the known blood types of his children and spouse. To address this, we must consider the inheritance patterns of the ABO blood group system and the Rh factor.

First, let's clarify the inheritance of the ABO blood group system. The blood type alleles are IA for type A, IB for type B, and i for type O. Since type A and B are codominant to each other and both are dominant over type O, we can deduce that the woman with type A blood must be heterozygous (IAi), as she has a child with type O blood, which is only possible if she contributes the 'i' allele. The son's blood type is B, which means the father must have contributed the IB allele.

Since the Rh factor shows simple dominance, where R is dominant and r is recessive, the positive Rh factor of the daughter and the woman indicates the presence of at least one dominant R allele in both. The son's negative Rh factor signifies that in his case, both parents must provide the recessive r allele, so the father also carries at least one recessive r allele.

The father's possible genotypes could be IBiRr or IBiRR, which means his possible phenotypes could be B positive or B negative. Since we know he must have the IB and the Rh allele, the only matching option from the given list is C) B positive.

Answer 2

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.