Mechanisms of Evolutionary Change

Mechanisms Natural Selection Mutations Nonrandom Mating Gene Flow and Genetic Drift

Natural Selection Determining force of evolution Reproductive success of organisms affects the gene pool of the population.

Mutations Occur because of an error in DNA sequence Are random

Mutations Some mutations help, some hurt & some are neutral Mutations can create new alleles that are handed down One of the most important sources of variation in the gene pool.

Nonrandom Mating Simply put – organisms choose who they will mate Some will compete for mates. The “winner” will get to mate and those genes continue in the gene pool.

Nonrandom Mating Some organisms depend on instinctive behaviors like courtship rituals or mating dances. Females may choose their mate based on preference.

Gene Flow and Genetic Drift Gene flow determines gain or loss of genes as organisms move in and out of a population. Also referred to as migration. Gene flow can dramatically reduce variations in large populations because the gene pool is shared.

Gene Flow and Genetic Drift In smaller populations, changes due to catastrophic events are referred to as genetic drift.

Gene Flow and Genetic Drift Bottleneck effect is an example of genetic drift. If 75% of the population is wiped out due to an event, that leaves only 25% of the population to reestablish it. Those traits that survived will move forward into future generations.

Gene Flow and Genetic Drift Founder Effect – when a few organisms from a large population are transferred to a new location. Darwin’s Finches are a classic example.

Hardy Weinberg Principle If evolution did not occur, the mechanisms just discussed would be static or unchanging. It is possible to calculate the gene frequency of alleles in a population using the following formula: P2 + 2pq + q2 = 1