Principles of natural selection. 1) Individuals in a species vary.2) Some variations are heritable.3) More individuals are produced than the environment can support.4) Competition for resources occurs.5) Individuals with favorable traits (and genotypes) will survive and reproduce. 1)Founder Effect: A small population branches off from a larger one. This population may or may not be genetically representative of the large population from whence it came. As the population increases in size, a different gene pool will develop from that of the parent population. For example, Afrikaaners in South Africa are descended from about 30 Dutch families and show a high frequency or recessive diseases. The Amish also have their own groups of recessive disorders. 2)Population Bottleneck: A population is drastically reduced by an event such as a flood or volcanic eruption having little or nothing to do with the usual forces of natural selection. The individuals that survive may have rare alleles. The gene frequencies of these rare alleles would increase dramatically after the disaster. 1. Stabilizing selection Extreme individuals are eliminated and intermediate forms are favored. The mutant forms are probably eliminated quickly. 2. Disruptive selection
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