Population Genetics & Evolution

Individuals do not evolve but populations do

Genetic Equilibrium Occurs when the frequency of alleles remains the same over generations within a population

Genetic Equilibrium Gene pool - All of the alleles of a population’s genes

Genetic Equilibrium Allele Frequency - percentage of a specific allele in the gene pool

Genetic Equilibrium A population that is in genetic equilibrium is NOT evolving

Genetic Equilibrium Anything that affects the genes in a gene pool can change allelic frequencies, which will disrupt a population’s genetic equilibrium and result in the process of evolution

Mechanisms that disrupt a population’s genetic equilibrium Mutations: introduce new alleles into the gene pool & change allelic frequencies

Mechanisms that disrupt a population’s genetic equilibrium Genetic drift - alteration of allelic frequencies by chance events Occurs mainly in small populations that interbreed with each other

Example of Genetic Drift Allele for extra fingers & toes is 1 out of 14 in Amish people but 1 out of 1000 for the rest of the U.S. population

Mechanisms that disrupt a population’s genetic equilibrium Gene flow - transport of genes by migrating individuals Genes are lost from the gene pool when an individual leaves a population; genes are added when an individual enters a population

Mechanisms that disrupt a population’s genetic equilibrium *The 3 mechanisms previously described primarily affect evolution of small, isolated gene pools (like those on islands) but their effect is often insignificant in larger, less isolated gene pools*

Mechanisms that disrupt a population’s genetic equilibrium Natural selection - the most significant factor that causes changes in established gene pools, whether they are large or small There are 3 types of natural selection: stabilizing, directional, & disruptive

Stabilizing Natural Selection Favors the average individuals in a population Reduces variation in a population

Directional Natural Selection Favors individuals with one of the extreme variations of a trait Can result in rapid evolutionary change within a population

Disruptive Natural Selection Favors individuals with either extreme of a traits variation Can lead to evolution of 2 distinct species

The End