Transcript Genetic Equilibrium - APBiology2010-2011

Genetic Equilibrium
A population is a group of individuals of a
species that lives in the same area at the
same time
Allele Frequency
• The proportion of an allele in a population.
• The sum of allele frequencies is one or 100%
• p+q=1
The Hardy-Weinberg Principle
• The Hardy-Weinberg principle describes a
population that is not evolving
• If a population does not meet the criteria of
the Hardy-Weinberg principle, it can be
concluded that the population is evolving
• What factors would have to be ABSENT
for a population to not evolve?
Hardy-Weinberg Equilibrium
• The frequency of alleles and genotypes in a
population will remain constant from
generation to generation if the population is
stable and in genetic equilibrium.
• What factors influence allele frequency
in a population? Or, what factors cause
allele frequency to change?
Five conditions required in order for
a population to remain at HardyWeinberg Equilibrium
1.A large breeding population
2.Random mating
3.No change in allelic frequency due to
mutation
4.No immigration or emigration (gene flow)
5.No natural selection
When these conditions exist, the population
is “not evolving”. Populations are rarely in
“true” Hardy-Weinberg Equilibrium, but in
some populations the rate of change is so
slow that they “appear” to be at
equilibrium; then the population can be
analyzed to estimate allele and genotype
frequencies.
Estimate the Frequency of Alleles in a
Population: Hardy-Weinberg Equation
• p = the frequency of the dominant allele
(represented here by A)
• q = the frequency of the recessive allele
(represented here by a)
For a Population in Genetic Equilibrium
•
•
•
•
p + q = 1.0 (The sum of the frequencies of both
alleles is 100%.)
(p + q)2 = 1
So, p2 + 2pq + q2 = 1
The three terms of this binomial expansion
indicate the frequencies of the three genotypes:
p2 = frequency of AA (homozygous dominant)
2pq = frequency of Aa (heterozygous)
q2 = frequency of aa (homozygous recessive)
The allele for black coat is recessive. We can use the
Hardy-Weinberg equation to determine the percent of the
pig population that is heterozygous for white coat.
http://www.phschool.com/science/biology_place/labbench/lab8/samprob1.html