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Unformatted text preview: cal population
Theoretical
genetic models:
genetic
HardyWeinberg Equilibrium
HardyWeinberg HardyWeinberg Equilibrium
Principle
Principle
Designed as a simple model to account for and
estimate how alleles behave in populations
Develops a null model for behavior of genes in
populations
Model specifies what will happen to frequencies
of alleles and genotypes
Applies to all diploid sexual organisms HardyWeinberg model
HardyWeinberg
Assumptions of HardyWeinberg
There is no selection
All members contribute equally to gene pool
There is no mutation
No new alleles are created
There is no migration
All alleles stay in gene pool
There is a large population size
No random events = genetic drift
Panmixia
Mates are chosen randomly HardyWeinberg Equilibrium
Principle
Principle
Population = group of interbreeding individuals and
their offspring
Life Cycle
Adults produce gametes
Gametes combine to make zygotes
Zygotes grow up to become next generation of
adults
Track fate of Mendelian genes across generations
in a population
Find out if particular alleles become more or less
common over time HardyWeinberg
HardyWeinberg
Example:
Imagine that mice have a particular locus A
with two alleles: A and a
(Could also call them A1 and A2)
Track these alleles and follow them
through one complete turn of the life
cycle to see if frequencies change HardyWeinberg
HardyWeinberg
Example:
Assume adults choose their mates at random
Matings are random within the gene pool
Diploid organisms (2N), so each has two
alleles for the A locus
Meiosis (during gametogenesis) caused one
allele (either A or a) to be in each gamete for
the A locus HardyWeinberg
HardyWeinberg
Example:
Imagine 60% of eggs and sperm contain allele A
and 40% contain allele a
Frequency of A allele in gene pool is 0.6, of a
allele is 0.4
When egg and sperm meet, what proportion of
genotypes will be AA?
60% egg will be A, 60% sperm will be A:
0.6 X 0.6 = 0.36
36% of zygotes will have genotype AA 60% A, 40% a HardyWeinberg
HardyWeinberg
Example:
How many would be aa?
0.4 X 0.4 = 0.16
How many would be Aa?
0.6 X 0.4 X 2 = 0.48
Notice that 0.36 + 0.48 + 0.16 = 1
All possible genotype frequencies
will add up to one HardyWeinberg Equilibrium
Principle
Principle
If zygotes grow up, what will the frequency of A in
the next generation be?
AA is 36% All gametes carry A Aa is 48% Half will carry A, half will carry a aa is 16% All gametes carry a Frequency of A in next generation will be:
0.36 + (1/2)0.48 = 0.6 Frequency of a will be:
0.16 + (1/2)0.48 = 0.4 HardyWeinberg
HardyWeinberg
Example:
0.6 + 0.4 = 1
Allele frequencies are the same as in the first
generation
Allele frequencies are in equilibrium
The population does not evolve
If a population is in HardyWeinberg Equilibrium it
will never evolve
(=allele frequencies in pop. will NEVER change)
This is true regardless of starting allele frequencies HardyWeinberg Equilibrium
Principle
Principle
The General Case
Imaginary population
Single locus with A and a...
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This document was uploaded on 09/17/2013.
 Fall '13

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