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Conditions for Hardy-Weinberg Equilibrium
1. 
2.
3.
4.
5.
Random mating No natural selection
No net mutation
No gene flow
Large population size
Random mating
Non-random mating
mating combines alleles
into genotypes
non-random
allele combinations
Non-random Mating
•  Will not change the overall allele frequencies; will change
_______________ frequencies
•  Inbreeding coefficient (F) =
Inbreeding and genetic diversity
• Loss of genetic diversity may
mean a species is not able to
adapt to a changing
environment
• Example?
Non-random mating: Inbreeding
•  Inbreeding depression:
Deleterious Recessive Alleles
•  How does natural selection drive
frequencies of deleterious recessive alleles
down?
Deleterious Recessive Alleles
•  Heterozygotes don’t express the deleterious
phenotype
•  Albinism: –  1/20,000 people are albino (aa)
–  f(a)= 0.007; f(aa) = 0.00005; f(Aa) = 0.014
–  280X as many heterozygote carriers than
albino homozygotes
Sexual Selection
occurs when individuals vary in their ability to compete with
others for mates or to attract
members of the opposite sex.
.
Intrasexual selection
Intersexual selection
Should natural selection act similarly on the
sexes?
•  Parental Investment:
Anisogamy: # of individuals having offspring Reproductive success
Males Females # of offspring Sexual Dimorphism
IntERsexual Selection
•  Female choice
•  Potential benefits of picking the right male:
–  Direct benefits:
–  Good genes :
Direct Benefits: Good Parents
house finch (Hill 1991; Navara et al. 2006 ) Symmetry
Symmetrical
Asymmetrical
Developmental homeostasis Net Mutation
•  Mutation is a weak force of evolution.
•  In a single generation, mutation produces
very little change in allele & genotype
frequencies.
Net Mutation
•  Mutational equilibrium (no net mutation):
rarely achieved
Lenski Experiment
Selection Maintains Polymorphism
•  Heterozygote Advantage (Overdominance): •  Example:
•  Frequency-dependent selection
–  Selection changes depending on the frequency of
each allele
Frequency-Dependent Predatory Selection
•  An allele has a selective advantage when it is the rarer
allele. Examples:
Gene flow
•  Strong evolutionary force •  Migration tends to make populations _____ _______
gg Gg GG gg GG GG gg Gg GG GG