文档介绍：Chapter 2
Changes of gene frequency in a large random mating population
Migration
m = proportion of new immigrants
qm = gene frequency among the immigrants
The frequency of A2 after migration:
Change of the gene frequency:
q0 = gene frequency in the original population
Mutation
Mutation rate:
Change of gene frequency:
when equilibrium attained(q = 0)
Two basic facts:
- the mutation rates in anisms are generally very low, about 10-5 ~ 10-6 per generation
- the reverse mutation is generally much less frequent than forward mutation
Selection
Complete dominance of A1, selection against A2
Selection
s=
s=1
q
Effect of selection on gene frequency for different initial frequencies
Selection
s=
s=1
Changes of gene frequency in the selection process
Selection
Generations needed for achieving a certain gene frequency(for s = 1)
Equilibria
Balance between mutation and selection
Change due to mutation
Change due to selection
(plete recessive allele)
When equilibrium attained
When v and q both very small
Polymorphism
Definition: if the largest allele frequency at a locus <
Measure of ic variation due to polymorphic loci
Heterozygosity
single locus: frequency of heterozygote, H
multiple loci: mean frequency of heterozygotes
Proportion of polymorphic loci among those tested
Polymorphic information content (PIC)
Polymorphism
Reasons
Heterozygote advantage
Frequency-dependent selection
Heterogeneous environment
Transition
Neutral mutation