1 Review Define genetic drift Relate Cause and Effect How can the founder effect lead to changes in the allele pool 2 Infer Genetic equilibrium is uncommon in actual populations. Why do you think this is the case 3 Evolution Do you think populations stay in genetic equilibrium after the environment Has changed significantly- explain.

Ch 17 Evolution of Populations 17.2 Evolution as Genetic Change in Populations

Insect populations often contain a few individuals that are resistant to a particular pesticide They pass on their resistance to their offspring and soon the pesticide-resistant offspring dominate the population.

Natural Selection on Single-Gene Traits Lead to changes in allele frequencies and then to evolution Mutation in one gene that determines body color in lizards can affect their lifespan The normal color for lizards is brown, a mutation may produce red and black forms.

Red lizards are more visible to predators They are less likely to survive and reproduce = red allele is rare.

Black lizards can absorb sunlight Higher body temperatures may allow the lizards to move faster, escape predators, and reproduce.

Natural Selection on Polygenic Traits The fitness of individuals may vary from one end of the curve to the other Can affect the range of phenotypes and hence the shape of the bell curve.

Directional Selection Individuals at one end of the curve have higher fitness than individuals in the middle or at the other end Range of phenotypes shifts.

Stabilizing Selection Individuals near the center of the curve have higher fitness than at either end Keeps the center of the curve at its current position, but it narrows the overall graph.

Disruptive Selection Individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle Acts against the intermediate type and can create two distinct phenotypes.

Genetic Drift Random change in allele frequency.

Genetic Bottlenecks Change in allele frequency following a dramatic reduction in the size of a population A disaster may kill many individuals in a population, and the surviving population’s gene pool may contain different gene frequencies from the original gene pool.

The Founder Effect Allele frequencies change as a result of the migration of a small subgroup of a population.

Genetic Equilibrium Allele frequencies in the population remain the same Evolution is not occurring.

Hardy-Weinberg Principle All conditions that must occur for evolution not to occur Very large population No mutations Random mating No migration No natural selection.

Large Population Genetic drift has less effect on large populations Large population size helps maintain genetic equilibrium.

No Mutations If mutations occur, new alleles may be introduced into the gene pool, and allele frequencies will change.

Random Mating All members of the population must have an equal opportunity to produce offspring Individuals must mate with other members of the population at random.

Random Mating Non random mating examples Selective breeding Self pollination Artificial selection Sexual selection

Sexual Selection Individuals in a population showing a preference for mating with a certain phenotype or trait.

Sexual Selection

No Migration (No Gene Flow) Individuals who join a population may introduce new alleles into the gene pool Individuals who leave may remove alleles from the gene pool There must be no movement of individuals into or out of a population.

No Natural Selection All genotypes in the population must have equal probabilities of surviving and reproducing No phenotype can have a selective advantage over another.

Shuffling of genes during sexual reproduction produces many different gene combinations but does not alter the relative frequencies of alleles in a population.