Types of Natural Selection

Definitions.. Evolution is the change in a population’s genetic material (alleles) over generations.

Definitions.. Evolution is the change in a population’s genetic material (alleles) over generations. A population is in genetic equilibrium if it’s not evolving

Definitions.. Evolution is the change in a population’s genetic material (alleles) over generations. A population is in genetic equilibrium if it’s not evolving. If the population’s allele frequencies stay the same year to year then it’s not evolving.

Hardy-Weinberg Genetic Equilibrium Hardy-Weinberg equilibrium describes populations that are not evolving

Hardy-Weinberg Genetic Equilibrium Hardy-Weinberg equilibrium describes populations that are not evolving Genotype frequencies stay the same over time as long as certain conditions are met:

Hardy-Weinberg Genetic Equilibrium Hardy-Weinberg equilibrium describes populations that are not evolving Genotype frequencies stay the same over time as long as certain conditions are met: Very large populations No emigration or immigration No mutations Random mating No natural selection

Natural Selection (3 Types) Organisms best suited to their environment live to reproduce and pass on their genes Acts on a phenotype Varying types of selection

1. Directional Selection Individuals with a more extreme form of trait have higher fitness Suppose termites in an area begin to build deeper nests. Anteaters with long tongues could more effectively prey on termites than those with short or average tongue length Normal Distribution Distribution after Selection

2. Stabilizing Selection Having average form of trait has highest fitness Reduces extremes Blue curve shoes variation after a new predator is introduced. Predator can easilty capture the large, visible lizards and the small slower lizards. Thus, selection against these extremes body types reduces the size range in lizards Normal Distribution Distribution after Selection

3. Disruptive Selection Individuals with either extreme trait has a higher fitness and most likely results in two new species Divergent Evolution The white limpets blend in with barnacles on rocks. On bare rocks, dark-shelled limpets blend in. However, the tan colored limpets are easy to spot by birds. Normal Distribution Distribution after Selection