Download Hardy-Weinberg Equilibrium

 Gene Pool:
 All the genes of all the
members in a population.
 Allele Frequency:
 Percent of each allele in
the population.
 Genetic Equilibrium:
 Allele frequencies remain
the same from one
generation to the next.
The Hardy-Weinberg Theorem
 States the allele frequencies remain constant (Hardy-
Weinberg Equilibrium) unless acted upon by outside
agents.
 It best describes a nonevolving population.
 Very useful to establish baselines in populations.
Godfrey Hardy
(1877-1947)
Wilhelm Weinberg
(1862 – 1937)
Hardy Weinberg Theorem
 Populations remain stable under the following five
assumptions.
1. Populations must be large

Genetic Drift: allele frequencies change as a result of random events
or chance
2. No Migration
3. Random Mating
4. No Mutations
5. No Natural Selection
If one or more of these conditions
are not met, EVOLUTION occurs.
Tasters or Non-tasters??
 A = tasters
p
a = non-tasters
+
q
Phenotypes
Tasters
(p2 + 2pq )
#
%
Allele Frequency
Nontasters
(q2)
#
%
Class Population
N. American
Population
.55
1
=
.45
p
q
Hardy Weinberg Equation
 To estimate the frequency of alleles in a population, we can use the
Hardy-Weinberg equation. According to this 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
 (p + q)2 = 1
 so
100%.)
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)
Example
 Screech owls are found in two different color patterns, red
and gray. Scientists have raised and bred these owls in
captivity. The scientists mated red to red, red to gray and
gray to gray. The red to gray mating usually gave equal
numbers of red and gray offspring but sometimes gave only
red offspring.
 A population survey done in Pennsylvania showed the
population to be composed of 51% red and 49% gray owls
a. Which gene is dominant?
b. Calculate the frequency of each allele.
c. Calculate the frequency of each genotype.
d. Suppose the frequency of each gene (allele) for red
feathers is .42 ten years later in the same population. What
could have caused the change in the gene frequency?