Both genetic and environmental factors can cause phenotypic variation in a population. Different alleles can confer different phenotypes, and different environments can also cause individuals to look or act differently. Only those differences encoded in an individual’s genes, however, can be passed to its offspring and, thus, be a target of natural selection. Natural selection works by selecting for alleles that confer beneficial traits or behaviors, while selecting against those for deleterious qualities.
Genetic drift stems from the chance occurrence that some individuals in the germ line have more offspring than others. When individuals leave or join the population, allele frequencies can change as a result of gene flow. Mutations to an individual’s DNA may introduce new variation into a population. Allele frequencies can also be altered when individuals do not randomly mate with others in the group.
when individuals tend to mate with those who are phenotypically similar to themselves
magnification of genetic drift as a result of natural events or catastrophes
gradual geographic variation across an ecological gradient
flow of alleles in and out of a population due to the migration of individuals or gametes
effect of chance on a population’s gene pool
diversity of alleles and genotypes in a population
differences in the phenotypic variation between populations that are separated geographically
fraction of population variation that can be attributed to its genetic variance
mating of closely related individuals
increase in abnormalities and disease in inbreeding populations
changes in a population’s gene pool due to mate choice or other forces that cause individuals to mate with certain phenotypes more than others
distribution of phenotypes in a population
environmental factor that causes one phenotype to be better than another