With the assumption that the population follows Hardy-Weinberg equilibrium, it can be expected that it follows the equation p2 + 2pq + q2 + 2qr + r2 + 2pr = 1, where p is the allele frequency for IA, q for IB, and r for IO.
The other terms are defined below, along with their values:
p2 (0.09) is for the genotypic frequency for homozygous IAIA,
2pq (0.36) is for heterozygous IAIO,
q2 (0.36) is for homozygous IOIO,
2qr (0.12) is for heterozygous IBIO,
r2 (0.01) is for homozygous IBIB, and
2pr (0.06) is for heterozygous IAIB.
It should be noted that unlike systems with just two alleles, having three alleles would modify the other equation to p + q+ r = 1.
Human blood type is determined by three alleles, IA, IB, and IO. The alleles IA and IB are codominant to each other, and both are dominant to IO. Within a large, randomly mating population (540,000 individuals), the frequencies for the blood type alleles are 0.3 for the IA allele; 0.6 for the IO, and 0.1 for the IB allele.
a. Calculate the expected number of people in the population having each blood type A, B, AB, and O.
b. Determine the percentage of type B people that are heterozygous.
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