Population Genetics of the t and H-2 Systems

Abstract

A population is an assembly of individuals sharing a common gene pool, that is, the group of genes from which those of the next generation are chosen. Genetic constitution of a population is defined by the gene and genotype frequencies calculated from the corresponding phenotype frequencies. Phenotype (genotype, gene) frequencies are obtained by counting the individuals carrying the particular phenotype (genotype, gene) and dividing the sums by the number of individuals in the population. The frequencies are expressed as percentages (0–100 percent) or fractions, ranging from 0 to 1. All phenotype frequencies and the genotype frequencies for dominant genes are obtained by direct counting; genotype frequencies for recessive genes are computed using special statistical methods. Gene frequencies are calculated from genotype frequencies as illustrated by the following example. Take two genes, A1 and A2, and their frequencies, p and q, respectively, where p+q = 1. Consider three genotypes, A1A1, A1A2, and A2A2, and their respective frequencies P, H, and Q, where P+H+Q = 1. The relationship between gene and genotype frequencies is then expressed by the equations $$\begin{array}{*{20}{c}} {p = P + \tfrac{1}{2}H} \\ {q = Q + \tfrac{1}{2}H} \\ \end{array}$$