The ABO blood group assorts independently of the rhesus (Rh) blood group and both assort independently of the MN blood group. Three alleles, I^A, I^B and i, occur at the ABO locus. Two alleles, R, a dominant allele producing Rh+, and r, a recessive allele for Rh-, are found at the Rh locus, and codominant alleles M and N occur at the MN locus. Each gene is autosomal.

A child with blood types A, Rh−, and M is born to a woman who has blood types O, Rh−, and MN and a man who has blood types A, Rh+, and M. Determine the genotypes of each parent.

Key Concepts

ABO Blood Group System

The ABO blood group system is determined by the presence of three alleles: I^A, I^B, and i. The I^A and I^B alleles are codominant, meaning that if both are present, both will be expressed, resulting in blood type AB. The i allele is recessive, so an individual must have two i alleles to express blood type O. Understanding this system is crucial for determining the possible genotypes of parents based on their children's blood type.

Rh Factor

The Rh factor is determined by two alleles: R (dominant) and r (recessive). An individual with at least one R allele will have Rh+ blood, while only those with two r alleles will have Rh- blood. This concept is essential for analyzing the Rh status of the parents and the child, as it influences the inheritance patterns of the Rh blood group.

MN Blood Group System

The MN blood group system is defined by two codominant alleles, M and N. An individual can have one of three genotypes: MM, MN, or NN, which correspond to the blood types M, MN, and N, respectively. This system is important for understanding the inheritance of the MN blood type in the child and how it relates to the genotypes of the parents.