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Preservation of Genetic Variation. Diploidy : because there are 2 alleles genetic variation is hidden from selection in the form of recessive alleles Balancing selection : natural maintains two or more forms in a population. Includes :
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Diploidy: because there are 2 alleles genetic variation is hidden from selection in the form of recessive alleles • Balancing selection: natural maintains two or more forms in a population. Includes: • heterozygote advantage: when natural selection tends to maintain two or more alleles at a specific locus • Frequency dependent selection: fitness of a phenotype declines if it becomes too common in a population • Neutral Variation: When no selective advantage or disadvantage of nucleotide sequences appear
Natural Selection Cannot Fashion Perfect Organisms • Selection can only act on existing variations • Evolution is limited by historical constraints • Adaptions are often compromises • Chance, natural selection, and the environment interact