1. Hardy -- Weinberg

2. When will a population evolve?
Godfrey Hardy ( )
Wilhelm Weinberg ( )
The Hardy-Weinberg principle states that the frequencies of alleles and genotypes in a population’s gene pool remain constant over the generations unless acted upon by agents other than recombination from sexual reproduction; populations do NOT evolve, unless they are NOT in H-W equilibrium

3. H-W equilibrium conditions and mechanisms of change

4. The Mechanisms of Change are the agents of evolutionary change
Gene Flow
Mutation
Selection
Non-random mating
Genetic Drift

5. Populations & gene pools
Concepts
a population is a localized group of interbreeding individuals
The gene pool is collection of alleles in the population
remember difference between alleles & genes!
allele frequency is how common an allele is in the population
Ex: 70% of individuals carry at least one dominant allele

6. Evolution of populations
Evolution = change in allele frequencies in a population
hypothetical: what conditions would cause allele frequencies to not change?
Let’s imagine a non-evolving population To stop evolution, REMOVE all agents of change
very large population size (no genetic drift)
no migration (no gene flow in or out)
no mutation (no genetic change)
random mating (no sexual selection)
no natural selection (everyone is equally fit)
*This is Hardy-Weinberg equilibrium*

7. Hardy-Weinberg theorem
Counting total Alleles (regardless of genotype)
assume 2 alleles = B, b
frequency of dominant allele = p
frequency of recessive allele = q
frequencies must add to 1 (100%), since all individuals have one or both so:
p + q = 1 BB Bb bb

8. Hardy-Weinberg theorem
Counting Individual genotypes
frequency of homozygous dominant genotype: p x p = p2
frequency of homozygous recessive genotype: q x q = q2
frequency of heterozygotes: (p x q) + (q x p) = 2pq
Again, frequencies of all individuals must add to 1 (100%), so:
p2 + 2pq + q2 = 1 BB Bb bb

9. NOTICE THE DIFFERENCE!!! Alleles: p + q = 1
Genotypes: p2 + 2pq + q2 = 1 B b BB Bb bb BB Bb bb

10. Using Hardy-Weinberg equation
Population of 100 cats. Black is dominant to white in fur color. 84 are black and 16 are white.
Can I determine the number of each genotype?
q2 (bb): 16/100 = .16
q (b): √.16 = 0.4
p (B): = 0.6
p2=.36
2pq=.48
q2=.16 BB Bb bb
Must assume population is in H-W equilibrium!
What are the genotype frequencies?

11. Online Practice http://bio1151.nicerweb.com/med/QUIZ/hw_q.html

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13. f

14. F

15. FF

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