EB chapter 6

What are Darwin’s 4 postulates in population genetics terms?

allelic variation exists among individuals

alleles are passed down from parent to offspring by meiosis + fertilization

more young are born than can survive

some allelic combinations are more fit than others and these survive to reproduce more often

Hardy-Weinberg equilibrium

null model for behavior of genes in populations

… specifies what will happen to frequency of alleles and genotypes

applies to all diploid sexual organisms

1st conclusion of HWE

allele frequency in a population will NOT change, generation after generation

2nd conclusion of HWE

if allele frequencies in a population are given by p and q, the genotype frequencies will be given by p², 2pq, and q²

Five Assumptions of HWE

no selection

no mutation

no migration

there is an infinitely large population size

panmixia

Why is HWE useful?

shows when evolution does not happen

gives specific testable assumptions

if assumptions are violated, conclusions do not hold

genotypes approximate a binomial distribution, after 1st gen mating

allows prediction of genotype frequencies given allele frequencies

…. they will not change as long as assumptions are met…

Adh case study

alleles Adh^f and Adh^s break down alcohol at different rates

maintained two populations of alleles spiked with alc and two controls w/out

Adh case study results

control= allele frequencies didn’t change (HWE)

under selection pressure= showed decline in Adh^s allele

hw conclusion 1 did not hold

How did the populations of Drosophila(Adh) evolve?

bec of selection for better ability to break down alc

What cannot be calculated by Hardy-Weinberg equation?

genotype frequency

W

fitness of an allele, ranges from 0-1

S

strength of selection on an allele

what is positive s ?

selection in favor of phenotype

what is negative S?

selection against phenotype

scale eating fish (frequency dependent selection)

one allele is favored over the other

it is better to be rarer type as they will be a successful predator and more fit, leaving more offspring

POPULATION always evolving for higher frequency of rarer phenotype