Transcript Ch 16 Sec 2
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 HardyWeinberg 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: a) 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. b) 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