Population Genetics The study of allele frequencies within

Population Genetics The study of allele frequencies within a population

Gene Pool • All of the genes of a population of organisms – Organisms that are the most successful at reproducing contribute most to the gene pool

Evolution • Any change in the frequency of any allele within a gene pool – Populations undergo evolution – Individuals do not undergo evolution

Factors Affecting the Allele Frequency • Mutation – Especially important for organisms with short generation times

Factors Affecting the Allele Frequency • Migration – Movement of organisms into or out of the population

Factors Affecting the Allele Frequency • Genetic Drift – Random change in allele frequencies – Occurs mostly in small, isolated populations

Factors Affecting the Allele Frequency • Selection – Environmental pressures – Competition – Climate change

Factors Affecting the Allele Frequency • Nonrandom mating – Preferences in selection of a mating partner

SPECIES Species: Species A group of organisms so similar to one another that they can interbreed and produce fertile offspring Kingdom Phylum Class Order Family Genus Species

Speciation • Speciation is the evolution of new species through time • Speciation occurs most rapidly in a small population

Mechanisms of Speciation • Artificial Speciation – New species have been developed by man Intentional mutations • Cross breeding • Genetic engineering •

Mechanisms of Speciation • Natural Speciation by Isolation of Small Populations – Geographical Isolation • Geographical barriers separate two populations – Mountain ranges – Deep canyons – Bodies of water – Ecological Isolation • Organisms of two populations require different habitats

Mechanisms of Speciation • Behavioral Isolation – Changes in habits that identify one population with another • Mating rituals • Methods of communication

Mechanisms of Speciation • Seasonal Isolation – Reproductive cycles do not coincide • Plants that flower at different times • Animals that mate or nest build at different times

Mechanisms of Speciation • Mechanical Isolation – Physical characteristics that keep organisms from interbreeding • Difference in size • Difference in reproductive anatomy • Inability of sperm to penetrate the egg

Observations From the Fossil Record • Species often remain stable for millions of years with little or no noticeable change • Species may disappear rapidly and new species may appear just as fast

Population Evolution

Punctuated Equilibrium Long periods of stability followed by short periods of rapid change