This tutorial covered the basic principles of population genetics. A population is a group of organisms that are members of the same biological species and that live in the same geographic area. Characters in a population can be monomorphic, showing no variation, or polymorphic, having at least two different variants. Variation can be caused by the organism's genotype or by environmental effects. The Hardy-Weinberg equation can be used to examine genetic variation within populations. In the case of two alleles for a gene, the sum of the frequency of the alleles equals 1 or 100%. This is represented by the equation p + q = 1. To determine the frequencies of the three possible genotypes, use the equation p2 + 2pq + q2 = 1. When the allele frequencies stay the same between generations, the population is in Hardy-Weinberg equilibrium. Hardy-Weinberg equilibrium requires that allele frequencies within a population remain the same from one generation to the next, as long as certain conditions (including no mutation, large population size, no migration, random mating, and no natural selection) are met. The next tutorial will explore the evolutionary forces that can cause changes in allele and/or genotype frequencies in a population; that is, changes that lead to evolution.
The Hardy-Weinberg equation can be used to determine the allele frequency in a population. Thus, it provides a useful tool to describe the degree of evolution that is taking place over successive generations. Not all populations are undergoing evolution at all times. In certain stable environments, many populations show no evidence for evolution. (Although if the conditions change, then evolution can take place.)
There are a number of conditions that predictably decrease evolution; namely: large populations that are more genetically stable compared to smaller populations; no migration/immigration by which new alleles are introduced or removed from a population; no mutations to introduce new alleles; random mating that allows all individuals equal access to all alleles and; no natural selection, which causes changes in allele frequencies due to fitness differences between individuals.
Conversely, opposing conditions increase the chance of evolution; namely: small populations are genetically unstable because they are susceptible to genetic drift; migration/immigration that allows alleles to enter or leave a population; mutations that introduce new alleles; nonrandom mating that can cause unequal access to all alleles; and natural selection that changes allele frequencies based upon an individuals' reproductive capacity and fitness.