16.2 Evolution as Genetic Change. The effects of Natural Selection cause changes in whole populations, not just in individuals. Therefore the genetics.

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Presentation transcript:

16.2 Evolution as Genetic Change

The effects of Natural Selection cause changes in whole populations, not just in individuals. Therefore the genetics of the population will change. Evolution of dolphins

Natural Selection on Polygenic Traits Natural Selection on Polygenic Traits Natural selection operates on variations of traits within a population. Natural selection operates on variations of traits within a population. The distribution of traits in a population changes over time. The distribution of traits in a population changes over time. There are 3 general patterns of trait changes in a population as a result of natural selection. There are 3 general patterns of trait changes in a population as a result of natural selection.

1. DIRECTIONAL SELECTION: An extreme phenotype becomes a favorable adaptation

2. STABILIZING SELECTION: The average phenotype is favored for survival. The extreme phenotypes are un-favored.

3. DISRUPTIVE SELECTION The average phenotype is not favorable, but the extreme phenotypes become favored adaptations. Can eventually lead to 2 species.

Hardy-Weinberg Principle Hardy-Weinberg Principle If the allele frequencies do not change, the population will not evolve. This will be true if 5 conditions are met. This will be true if 5 conditions are met. Flamingo population

Hardy-Weinberg Genetic Equilibrium Random mating. [Seldom happens.] Very large populations. [Can happen.] No immigration and no emigration. [Can happen.] No mutations. [Seldom happens.] No natural selection. [Seldom happens.]

Therefore, evolution is a given, it cannot be stopped. There are no conditions known under which evolution does not happen! Evolution of land animals

Genetic Drift Genetic Drift Happens in small populations. Happens in small populations. An allele becomes more or less common easier. An allele becomes more or less common easier. Random chance events lead to these changes in gene frequencies. Random chance events lead to these changes in gene frequencies. Bull Tule Elk at Pt. Reyes

Founder Effect Founder Effect Founding populations are completely separated from the original population, as well as from other founding populations when they colonize a new habitat.