Use the following information to answer the questions below.
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.
-If both children are of blood type M, which of the following is possible?
A) Each parent is either M or MN.
B) Each parent must be type M.
C) Both children are heterozygous for this gene.
D) Neither parent can have the N allele.
E) The MN blood group is recessive to the ABO blood group.

Question

Quizplus · Accepted Answer

CA) Since both children are of blood type M, it means they must have received an M allele from each parent. This allows for the possibility that each parent could be either homozygous M (MM) or heterozygous MN, as both could pass on the M allele to their children.C) Given that both children are of blood type M and assuming each parent contributed an M allele, the children would be homozygous (MM) for this gene, not heterozygous. This choice was incorrectly marked as correct based on a misinterpretation of the question's details. The correct interpretation should note that if both children are of blood type M and this trait is codominant, they could indeed be homozygous (MM), assuming each parent contributed an M allele. However, the question's phrasing about possibilities does not strictly exclude other genotypes for the parents, making the explanation for choice A valid. The initial explanation mistakenly identified an incorrect understanding of codominance and the inheritance of the M allele.

Use the Following Information to Answer the Questions Below