Human Genetics Problem Set

Problem 19: Who is NOT the father of my grandson?

"What are the types that the fathers would have to be in order for him (grandson) to be a B+?"

Tutorial

How did Professor Hallick respond to the concerned grandmother?

The child in question has blood type B. Since the mother is blood type A, the child must have received an O allele from the mother, and a B allele from the biological father. The mother's blood type is AO, the child is BO, and the father is either AB or B, which are the only two types that could be the source of a B allele.

If the father is type B, the genotype could be either BB (homozygous) or BO (heterozygous). If either of the two "gentlemen" in question has blood type O or blood type A, he can be excluded as being the biological father.

The child in question is Rh+. The Rh+ allele is at a different locus than the A, B, O alleles. Rh+ is dominant to Rh-. In this particular case, the father could be either Rh- or Rh+, and no discrimination on this factor is possible.

The Biology Project
University of Arizona
Thursday, June 5, 1997 Contact the Development Team