Читать книгу Principles of Plant Genetics and Breeding - George Acquaah - Страница 107

To understand the genetic structure of a population, consider a large population in which random mating occurs, with no mutation or gene flow between this population and others, no selective advantage for any genotype, and normal meiosis. Consider also one locus, A, with two alleles, A, and a. The frequency of allele A ₁ in the gene pool is p, while the frequency of allele A ₂ is q. Also, p + q = 1 (or 100% of the gene pool). Assume a population of N diploids (have two alleles at each locus) in which two alleles (A, a) occur at one locus. Assuming dominance at the locus, three genotypes – AA, Aa, and aa – are possible in an F₂ segregating population. Assume the genotypic frequencies are D (for AA), H (for Aa), and Q (for aa). Since the population is diploid, there will be 2N alleles in it. The genotype AA has two A alleles. Hence, the total number of A alleles in the population is calculated as 2D + H. The proportion or frequency of A alleles (designated as p) in the population is obtained as follows:

The same can be done for allele a, and designated q. Further, p + q = 1 and hence p = 1 – q. If N = 80, D = 4, and H = 24,

Since p + q = 1, q = 1 − p, and hence q = 1 – 0.2 = 0.8.