Disruption of Genetic Equilibrium Chapter 16 Section 2

Introduction Evolution is the change in a population’s genetic material over generations Change in a population’s allele frequencies Any exception to the Hardy- Weinberg equilibrium can result in evolution

Mutation Remember  the first condition for genetic equilibrium is no net mutations Mutations can affect genetic equilibrium by producing new alleles for a trait Most are harmful or have no effect The few beneficial mutations will be passed on and eventually build up in a population

Gene Flow Remember  The second requirement for genetic equilibrium is that the population size remains constant Gene Flow - If individuals move their genes move with them Immigration – Movement of individuals into a population Emigration – Movement of individuals out of a population

Genetic drift Remember  the third requirement of genetic equilibrium is the presence of a large population Genetic drift - the alteration of the gene pool of a small population due to chance. Northern Elephant seal – individuals are homozygous for all traits tested Lost their genetic variation Very susceptible to extinction

Two factors may cause genetic drift:                                      Bottleneck effect may lead to reduced genetic variability following some large disturbance that removes a large portion of the population. The surviving population often does not represent the allele frequency in the original population. Founder effect may lead to reduced variability when a few individuals from a large population colonize an isolated habitat.

Nonrandom Mating Remember  the fourth requirement of genetic equilibrium is random mating Most species do not mate randomly, often influenced by geographic proximity Sexual Selection – females chose the males they mate with based on certain traits

Extreme traits give the females an indication of the males fitness in his environment

Natural Selection Remember  the fifth requirement of genetic equilibrium is the absence of natural selection Natural selection means that some members of a population are more likely to survive and reproduce then others and contribute their genes to the next generation Scientists observe 3 patterns of natural selection

Disruptive Selection Individuals with either extreme of a trait have greater fitness then individuals with the average form of trait Ex. Limpet White shelled - found on rocks covered with white goose barnacles Dark shelled - found on bare rocks Intermediate individuals are easier to spot and get eaten by birds

Directional Selection Individuals with one extreme of a trait have greater fitness then other individuals Ex. Anteater – feeds by breaking open termite nests then pushes sticky tongue into nest to lap up termites Anteaters with a long tongue would be able to eat more termites, this extreme would be favored over all other sizes

Stabilizing Selection Individuals with average form of a trait have the highest fitness Extreme for of traits have lower fitness Ex. A very large individual may be easier to spot by predators. A small individual may not be able to run as fast