MUTATION

Mutations are changes in the structure of genes and chromosomes. The Hardy-Weinberg theorem assumes that no mutations occur or that mutational equilibrium exists. Mutations, however, are a fact of life. Most importantly, mutations are the origin of all new genes and a source of variation that may prove adaptive for an animal. Mutation counters the loss of genetic material from natural selection and genetic drift, and it increases the likelihood that variations will be present that allow a group to survive future environmental shocks.

   Mutations are random events, and the likelihood of a mutation is not affected by the mutation’s usefulness. Organisms cannot filter harmful genetic changes from advantageous changes before they occur. The effects of mutations vary enormously. Most are deleterious. Some may be neutral or harmful in one environment and help an organism survive in another environment.

   Mutational equilibrium exists when a mutation from the wild-type allele to a mutant form is balanced by mutation from the mutant back to the wild type. This has the same effect on allelic frequency as if no mutation occurred. Mutational equilibrium rarely exists, however. Mutation pressure is a measure of the tendency for gene frequencies to change through mutation.