ANT100Y1 Lecture 6: Biology-Lecture 6-Chapter 11-Human Variation Oct 16 2008
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O directional selection: a type of natural selection that increases the frequency of a trait (the trait is said to be positively favored, or adaptive) O normalizing selection: the type of natural selection that removes harmful genes that arose by mutation. O balancing selection: a type of selection that occurs when a heterozygous combination of alleles is positively favored even though a homozygous combination is disfavored. O natural selection does not account for variation in frequencies of neutral traits. O similar frequencies of neutral traits in human populations may result, then, from genetic drift or gene flow. O natural selection may favour certain genes because of certain physical environmental conditions, as in the case of the moths in england (dark/light moths- industrialization-> newly darkened trees; predators could not see dark moths= soon outnumbered light moths) O physical environment can sometimes produce variation even in the absence of genetic change.
