This problem refers to the MN and ABO loci mentioned in class. It also refers to

Question

This problem refers to the MN and ABO loci mentioned in class. It also refers to the Rh locus, which is responsible for the positive/negative part of the blood type. The Rh+ allele is dominant to the Rh- allele at this locus. Select all couples who could be the parents of a child with phenotype N, AB- based on the phenotypes at these three loci. If none of these couples could be the parents of this child, select "None of These".

Select one or more:

Mother Type M, A+ and Father Type N, B-

Mother Type MN, AB- and Father Type M, O-

Mother Type MN, B+ and Father Type N, O+

Mother Type MN, O+ and Father Type MN, A-

None of These

Explanation / Answer

We first need to know that MN alleles are codominant in nature. So in heterozygous form (MN) both alleles are expressed.

Now the question says we need a couple whose offspring will have N phenotype and AB blood group with Rh negative phenotype.

So to get only N allele in the child, firstly both mother and father need to carry N allele only. If either one of them carry M allele then it will be expressed as the allele is co dominant.

Here in all options the mother carries the M allele with or without the N allele, so the child will carry M allele which is not desirable according to the question.

Therefore the correct OPTION IS - NONE OF THESE.

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