BIO 416 Evolution Lecture #12 Population Genetics III Destabilizing The Equilbrium February 9, 2009 Dr. Karen Schmeichel Oglethorpe University Hardy Weinberg

Business: Lit Rev #1 Due 2/11 Darwin’s Birthday 2/12 – (10 pts) Exam 2/13 – Study Guide on Wednesday Exam – Through Ch 7

Objectives: Reconsider H-W equilibrium using Card Simulations Discuss Factors that destabilize H-W Cover the ways in which selection can alter changes in allelic and genotypic frequencies

Hardy-Weinberg Equilibrium: a Null Model 1.Allele frequencies in a population will not change, generation after generation 2.If the allele frequencies are given by p and q, the genotype frequencies will be given by p 2, 2pq and q 2

5 Hardy-Weinberg-Castle Equilibrium: Describes how allele and genotype frequencies do not change during the course of many generations, unless destabilizing conditions exist p 2 +2pq + q 2 = 1 f(AA)f(Aa)f(aa)

= 0.8= 0.2 = 0.8 = 0.2 = 0.8 x 0.8 = 0.8 x 0.2 = 0.2 x 0.2 f(AA) =.64 f(Aa) =.32 f (aa) =.04 Another Way to conceptualize HW:

7 In a given population with alleles A and a: p + q = 1

A Population in H-W Equilibrium will show same allelic frequency generation after generation (RARE, if ever!)

A Population Genetics Simulation

HW Equilibrium is Predictive

HW Equilibrium: a Null Model 1.Allele frequencies in a population will not change, generation after generation 2.If the allele frequencies are given by p and q, the genotype frequencies will be given by p 2, 2pq and q 2

How to “mind your p’s and q’s”?

14 Alloenzymes & Orchid Exercise

Heterozygosity as a Measure of Genetic Diversity: The average individual is heterozygous at 4-15% of its genes

Hardy Weinberg Conditions: Allele and genotype frequencies will not change from generation to generation if: 1.No selection 2.No mutation 3.No migration 4.No genetic drift 5.Mating is random

Can Selection Change allele frequencies from one generation to the next? (Game Rule: 75% of the heterozygotes survive and 50% of the homozyg recessives survive)

Violation of Conclusion #1

Violation of Conclusion #2 Papua New Guinea’s Fore Tribe and Kuru

23 Dogma Following the Modern Synthesis: Natural Selection should preserve the allele most conducive to survival and reproduction and eliminate the rest. The one best allele was called wild type and any other alleles were considered mutants (extremely rare).

Natural Selection Is most potent When a recessive Allele is common, Not rare (think: heterozygote) FAST!SLOW!

Selection Favoring Heterozygotes: “Overdominance” (ex, Fig in Fruit Flies) A way of maintaining recessive alleles Selection Favoring Homozygotes: “Underdominance” (ex, Fig 6.19 in Fruit Flies) In this case, one allele tends to go to fixation, while the other allele is lost (may be different in different populations)

For 2/11: Ch 7 & Prairie Chicken Paper

Mutation Alone Causes Slow Change Over Time – Generally A weak Mechanism for Evolution

Mutation + Selection: The 1-2 Punch

Mutation/Selection Balance (or frequency of deleterious allele at equilibrium) is Described Mathematically: q =   s