Populations, Gene Pools, & Microevolution Chapter 13

What you need to know! How mutation and sexual reproduction each produce genetic variation. The conditions for Hardy-Weinberg Equilibrium. How to use the Hardy-Weinberg equation to calculate allelic frequencies and to test whether a population is evolving.

Evolution & Gene Pools A single organism does not evolve One animal has the genes it was born with and they do not change Populations evolve Populations are multiple animals of a single species (that can interbreed) All the genes/alleles in a population are called a gene pool Microevolution is the change of a species’ relative frequencies of alleles

Relative Frequencies The number of times alleles appear in a gene pool divided by the total number of alleles What are the Relative Frequencies of fur color for these mice? Relative Frequency: Brown: 30/50, Black: 20/50 Sample Population Frequency of Alleles allele for brown fur allele for black fur 48% heterozygous black 16% homozygous black 36% homozygous brown

Sources of Microevolution Natural Selection: differential reproductive success of certain phenotypes lead to a(n) increase/decrease of certain alleles Mutation: introduces new alleles Gene flow: add or remove alleles to a gene pool based on migration

Sources of Microevolution Genetic Drift: Random change of allele frequency in small populations Founder Effect: spike in gene change due to genetic drift after a small population inhabits a new region Bottleneck effect: a small surviving group (near extinction) gives rise to a new population with a dramatically different gene pool

Sources of Microevolution Sexual Selection: choosing mates based on heritable characteristics Sexual dimorphism: differences between males and females of the species Distance: Mating more often occurs between close neighbors than distant neighbors Inbreeding: reproduction with close relatives in small populations

Genetic Equilibrium In 1908, 2 mathematicians (Hardy & Weinberg) stated that the allelic frequency in a given population accounts for changes in populations They developed the concept of genetic equilibrium: how alleles in a population stay constant from one generation to another (no evolution)

Equilibrium Requires No natural selection No mutations No gene flow No genetic drift Random mating