Importance of HardyWeinberg

1
Importance of Hardy-Weinberg

• Null model for evolutionary genetics
• Makes basic assumptions
• Provides key insights into
• changes in genetic variation
• evolution of populations

2
Inbreeding
3
Consequences of Inbreeding

• Where are rare alleles in
• large populations?
• small populations?
• What if the allele is
• lethal?
• beneficial?
• Implications for population size?

4
Genetic Drift
Loss of alleles reduces genetic variation.
Random loss or fixation of alleles.
Non-adaptive evolution of population.
http//darwin.eeb.uconn.edu/simulations/jdk1.0/dri
ft.html
5
Consequences of Drift

• Alleles fluctuate due to random chance
• One allele drifts to fixation (p 1.0)
• Probability of fixation initial frequency (p)
• Drift causes loss of heterozygosity
• Faster in smaller populations
• Replicated populations diverge over time
  Non-adaptive Evolution

6
Effective Population Size

• Number of individuals in an ideal pop. in which
  rate of drift is identical to overall pop.
• measured by rate of loss of heterozygosity

7
Effective Population Size

• 500 individuals
• 200 males
• 300 females
• Monogamous
• 11 ratio
• Ne 400

8
Effective Population Size

• 500 adults
• 250 each sex
• Males haremic
• 5 females / male

• Only 50 males breed
• Ne 167
• Ne 4(NmNf)/(NmNf)

9
Founder Effect
10
Pingelap Atoll
Hawaii
Australia
11
Pingelap Atoll
12
Achromatopsia
13
Achromatopsia
14
Tie Back to Hardy-Weinberg
Violation of Infinite Population Size
Assumption Genetic Drift
15
Migration
Consequence? Allele frequencies change
16
Mutation
Consequence? Allele frequencies change
17
Genetic Drift
Loss of alleles reduces genetic variation.
Random loss or fixation of alleles.
Non-adaptive evolution of population.
http//darwin.eeb.uconn.edu/simulations/jdk1.0/dri
ft.html
18
Consequences of Drift

• Alleles fluctuate due to random chance
• One allele drifts to fixation (p 1.0)
• Probability of fixation initial frequency (p)
• Drift causes loss of heterozygosity
• Faster in smaller populations
• Replicated populations diverge over time
  Non-adaptive Evolution

19
Effective Population Size

• Number of individuals in an ideal pop. in which
  rate of drift is identical to overall pop.
• measured by rate of loss of heterozygosity

20
Effective Population Size

• 500 individuals
• 200 males
• 300 females
• Monogamous
• 11 ratio
• Ne 400

21
Effective Population Size

• 500 adults
• 250 each sex
• Males haremic
• 5 females / male

• Only 50 males breed
• Ne 167
• Ne 4(NmNf)/(NmNf)

22
Founder Effect