Based on the following results, select the best conclusion: Mother MM R0R0; Alleged father MM rr; Child MN R0r; the alleged father is

Based on the following results, select the best conclusion: Mother MM R0R0; Alleged father MM rr; Child MN R0r; the alleged father is

• A. Excluded by his M antigen
• B. Homozygous for R0
• C. Heterozygous for MN
• D. Not related

Answer: (A)

The main idea is how MN inheritance works. The MN blood group is governed by two codominant alleles, M and N. To express MN in a child, the child must inherit one M and one N allele. The mother is MM, so she can only pass M. That means the child must receive the N allele from the father. The alleged father is MM for MN, meaning he can only pass M and has no N allele. He cannot contribute the required N to produce an MN child. Therefore, he cannot be the biological father of a child with MN phenotype, so he is excluded. The Rh findings (mother R0R0, father rr, child R0r) are consistent with paternal contribution of the R0 from the mother and r from the father, but the MN result rules him out.

The main idea is how MN inheritance works. The MN blood group is governed by two codominant alleles, M and N. To express MN in a child, the child must inherit one M and one N allele. The mother is MM, so she can only pass M. That means the child must receive the N allele from the father. The alleged father is MM for MN, meaning he can only pass M and has no N allele. He cannot contribute the required N to produce an MN child. Therefore, he cannot be the biological father of a child with MN phenotype, so he is excluded. The Rh findings (mother R0R0, father rr, child R0r) are consistent with paternal contribution of the R0 from the mother and r from the father, but the MN result rules him out.