97_09_LB_PopGen2

# 97_09_LB_PopGen2 - Bio 97 Population Genetics II Last Time...

This preview shows pages 1–4. Sign up to view the full content.

1 Population Genetics II ©1999-2005 Lee Bardwell Bio 97 Last Time 1. The Hardy-Weinberg Equation 2. Hardy-Weinberg Equilibrium 3. How to use HW 4. Forces that can cause deviation from HW ratios ©2009 Lee Bardwell Population Genetics Allele freqs Genotype freqs Gene pool Hardy Weinberg Law: ©2001 Lee Bardwell A a AA Aa aa (p+q) 2 = p 2 +2pq +q 2 = 1 HW equilibrium: allele freqs remain constant from generation to generation, under certain conditions Try using both allele counting methods to determine the allele freqs in a pop of 10 people , consisting of 1 homozyg w.t , 6 hets and 3 homozyg recessive At home exercise - Method 1: just count (there are 20 alleles total) Method 2: p = freq(AA) + 1/2 freq(Aa), q = freq(aa) + 1/2 freq(Aa),

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
2 Try using both allele counting methods to determine the allele freqs in a pop of 100 people , consisting of 10 homozyg w.t (AA) , 60 hets (Aa) and 30 homozyg recessive (aa) Let’s assume this pop is 10X larger so we don’t have to worry about drift* Is this pop at HW equil? *in reality would have to be much larger Forces that can cause deviation from HW ratios 1. Gene flow (e.g., migration) 2. Genetic drift 3. Mutation 4. Natural Selection 5. Non-random mating (e.g., inbreeding) ©2005 Lee Bardwell You would think that NS would eliminate “bad” (lower fitness) alleles from the gene pool. But then why do we still have disease-causing alleles in our gene pool? Natural Selection ©2009 Lee Bardwell Forces that keep “bad” alleles in gene pools Delayed age of onset (e.g. Huntington’s) Slow selection against recessive alleles in diploids Mutation-selection equilibrium Heterozygote superiority ©2000 Lee Bardwell Sometimes, bad alleles become good Natural Selection
3 Forces that keep “bad” alleles in gene pools Delayed age of onset (e.g. Huntington’s) Slow selection against recessive alleles in diploids Mutation-selection equilibrium Heterozygote superiority ©2009 Lee Bardwell Natural Selection A very weak selective advantage can still lead to a dominant allele becoming fixed (= essentially the only allele in

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

## 97_09_LB_PopGen2 - Bio 97 Population Genetics II Last Time...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online