Typically we talk about blood types as B-positive or AB-negative and so forth. The

positive and negative part of the blood type is determined by a completely separate gene (the
Rh locus). The ABO locus and the Rh locus are inherited independently, like pea shape and
pea color. The positive phenotype is dominant to the negative phenotype. A father has
genotype IA IO Rh+Rh– and a mother has genotype IA IB Rh+Rh–.
a. What are the phenotypes of these parents?
b. What is the probability that their only child will have phenotype B-positive?

To determine the phenotypes of the parents, you need to understand how blood type and Rh factors are inherited. Let's break it down step by step:

a. Phenotypes of the parents:
- The father has the genotype IA IO Rh+ Rh–. Based on the genotype, we can determine the blood group and the Rh factor separately:
- The ABO blood group genotype IA IO indicates that the father has blood group A (genotype IA) and carries the genetic variant for blood group O (genotype IO).
- The Rh genotype of Rh+ Rh– indicates that the father is positive for the Rh factor.

Therefore, the father's phenotype is A-positive (blood group A and Rh+).

- The mother has the genotype IA IB Rh+ Rh–. In a similar manner, we can determine her blood group and Rh factor:
- The ABO blood group genotype IA IB indicates that the mother has blood group AB, as she has the genetic variants for both blood groups A (genotype IA) and B (genotype IB).
- The Rh genotype of Rh+ Rh– tells us that the mother is positive for the Rh factor.

Thus, the mother's phenotype is AB-positive (blood group AB and Rh+).

b. To determine the probability of their only child having the phenotype B-positive, we need to understand how the genotypes can be combined during inheritance.

The possibilities for the child's blood type can be determined by combining the ABO genotypes of the parents: IA and IB.

The possible genotypes for the child are:
- IA IA (blood group A)
- IA IB (blood group AB)
- IA IO (blood group A)
- IB IB (blood group B)
- IB IO (blood group B)
- IO IO (blood group O)

Since the Rh factor is dominant, if either parent carries the Rh+ allele, the child will be Rh-positive.

Out of the six possible genotypes, only the genotype IB IB will result in a B-positive blood type.

Therefore, the probability that their only child will have the phenotype B-positive is 1 out of 6, or approximately 16.67%.