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Unformatted text preview: 1 Monday evening • Morning SNAFU – Question (thanks to Alp) • Does balancing selection result necessarily in evolution? – Tail in of Natural Selection Lecture: lost slides. • We will do those. • Evening Session—Marquez and epidemics Heterozygote advantage & Heterozygote advantage & warfarin warfarin resistance resistance in Norway rats: the data please in Norway rats: the data please … 1.000 0.378 0.568 0.568 0.054 Observed Frequencies 1.000 0.437 0.448 0.448 0.115 H-W Expected Frequencies TOTAL W r W r W s W r W s W s Observed Observed f(W f(W s ) = 0.339 ) = 0.339 Observed Observed f(W f(W r ) = 0.661 ) = 0.661 Does Heterozygote Advantage lead to Does Heterozygote Advantage lead to shifting allele frequencies through time? shifting allele frequencies through time? Observed Observed f(W f(W s ) = 0.339 ) = 0.339 Observed Observed f(W f(W r ) = 0.661 ) = 0.661 1.000 Observed Frequencies 1.000 0.437 0.448 0.448 0.115 H-W Expected Frequencies TOTAL W r W r W s W r W s W s 1.000 Observed Frequencies 1.000 H-W Expected Frequencies TOTAL W r W r W s W r W s W s F2 F3 broadened unchanged Disruptive narrowed changed Directional narrowed unchanged Stabilizing Variance in trait value Mean Trait value TYPE OF SELECTION A word about mortality and natural selection Frequency Frequency-dependent selection in scale dependent selection in scale-eating cichlids eating cichlids Hori (1993) Science 260 : 216 Perissodus Perissodus microlepis microlepis Left Left-mouthed mouthed P. P. microlepis microlepis attack attack right flank of prey right flank of prey Right Right-mouthed mouthed P. P. microlepis microlepis attack attack left flank of prey left flank of prey Sample Year Sample Year Frequency left Frequency left-mouthed fish mouthed fish 2 Positive versus negative frequency dependence • Positive frequency dependence – The more common a particular trait, the more the trait is favored • Negative frequency dependence – The less common a particular trait, the more the trait is favored. Negative Frequency Dependent Selection Gamoetophytic Gamoetophytic self self-incompatibility genes incompatibility genes Almonds (and many, many other plants) Almonds (and many, many other plants) Rare advantage frequency dependence An agricultural problem • Gametophytic self-incompatibility allows individuals to avoid selfing and maintains high genetic variability.genetic variability....
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This note was uploaded on 10/08/2009 for the course BIS 2 taught by Professor Schwartzandkeen during the Spring '09 term at UC Davis.
- Spring '09