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Mechanisms of Evolutionary Change (other than natural selection) SC.912.L.15.14 What can change a gene pool other than natural selection? 1. 2. 3. Genetic Drift Gene Flow Mutations Genetic drift Genetic Drift: A change in the gene pool of a population due to chance the smaller the population is, the more impact genetic drift has on that population Only the alleles of organisms that successfully reproduce in one generation appear in the gene pool of the next generation. In this population of ten plants, the frequency of white-flower alleles was reduced to zero due to genetic drift Genetic Drift Bottleneck Effect Disasters such as earthquakes, floods, droughts, and fires may drastically reduce the size of a population Reducing the size of the population also reduces the size of its gene pool By chance, certain alleles may then be represented more frequently than others among the survivors Some alleles may be eliminated altogether Decreases genetic variation in a population Marbles falling through the narrow neck of a bottle serve as an analogy for the bottleneck effect. Compared to the original population (in the bottle) the new population has less variation. The loss of variation due to a bottleneck effect could reduce the ability of a population to adapt to environmental change The Cheetah May have suffered one or more bottleneck events Sharp decrease in the cheetah population occurred during the last ice age about 10,000 years ago Farmers hunted the animals to near extinction The cheetah populations may not be able to resist disease or adapt to other environmental challenges to their survival Bottleneck Effect What else can effect the gene pool? Gene Flow Mutation Gene flow: The exchange of genes with another population 1. 2. Occurs when fertile individuals or their gametes (sex cells) migrate between populations Can increase or decrease genetic variation within a population Tends to reduce genetic differences between populations Mutation Mutation: a change to the genetic material Natural selection or genetic drift (or both) can influence whether the frequency of a new mutation increases in a population Example- albino deer Plays a key role in evolution as the original source of the genetic variation that is the raw material for natural selection Especially important as a source of variation in asexually reproducing organisms that clone themselves rapidly, such as bacteria Make a Venn Diagram Compare and contrast Genetic Drift, Gene Flow, and Mutations Venn Diagram