Overview

Natural populations of most plants and animals are genetically diverse, and a sizeable fraction of their genes have two or more common alleles. Population genetics is about the frequencies of alleles in populations and how these allele frequencies change from generation to generation. This chapter describes the following:

• The relation between allele frequencies and genotype frequencies in populations

• The magnitude of genetic variation in populations, and how it is measured

As with Mendelian theory and experiments, in population genetics one should focus attention first and foremost on gametes and haplotypes.

Populations

A population is a group of organisms of one species, living in one area. An asexual population is a clone, while a population of sexually reproducing, freely interbreeding eukarya is sometimes called a deme. In diplontic species, population size is defined as the number of all diploid individuals in that population, N. The copies of a gene in a population comprise a gene pool, and the size of the gene pool for diplontic species is 2N.

Predicting Genotype Frequencies from Allele Frequencies

Populations in Static Equilibrium

Consider gene A, an autosomal gene with two alleles, A1 and A2; the gametes in this population carry either A1 or A2. The frequency of A1 gametes is p and the frequency of A2 gametes is q, where p + q = 1.