Extra Problem 2.

  The genetics of the Rh blood type system are very simple: there are two types of alleles denoted + and -, with + dominant. Thus, the genotypes + + and + - both lead to the phenotype +, which only the genotype - - gives rise to a phenotype -.

The observed phenotype frequencies among North American caucasians is about 84% Rh + and 16% Rh -.

Let p denote the frequency of the + gene, and q = 1-p denote the frequency of the - gene.

(a) Assuming the Hardy - Weinberg principle, estimate the frequency q of the - gene from the given data on phenotype frequencies.

(b) Using your result from (a), compute the frequency of the + + and + - genotypes.

(c) Suppose you know that a mother has an Rh + phenotype, and her child is Rh -. Compute the conditional probability that the father is Rh - given the child's phenotype.