L48 Anthro 150A Lecture Notes - Lecture 5: Monomorphism, Disruptive Selection, Total Variation
16 Sep 2016
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Balancing selection: selecting for the heterozygote instead of the homozygote: ex: sickle cell, in areas with malaria sickle cell allele frequencies can be higher than 20% Complex genetic traits: characterized by continuous distributions rather than finite numbers of discrete values. 0 means no genetic variation; 1 means all variation is genetic ex fingerprint is 0. 9 and weight is 0. 3: stabilizing selection: selection against extremes of phenotypic distribution, decreasing genetic diversity of trait and going towards average of trait. Human birthweight is combination of genetic and environmental factors. Selection occurs against both extremes, both very small and very large babies have complications. Mortality rate is highest near extremes of newborn birthweight: directional selection: selection for one allele over others causing the allele frequencies to shift in one direction. There"s been a threefold increase in brain size over 4 million years. Only selecting against one extreme of the continuous trait: disruptive selection: selection for both extremes of phenotypic distribution.
