Monday, September 10, 2012
Purpose of H-W Principle:
The Hardy-Weinberg Principle
provides a baseline for comparison &
determines whether or not gene
frequencies have changed in a
population and thus whether
(micro)evolution has occurred.
Hardy-Weinberg Assumptions
• Very large population size
• No migration
• No net mutation
• Random Mating
• No natural selection
Hardy-Weinberg Equations:
p = frequency of allele 1 in gene pool
q = frequency of allele 2 allele in gene pool
Frequencies can be expressed as decimals (0.4)
or percentages (40%)
p+q=1
Hardy-Weinberg Equations:
Allele frequency is used to predict genotype
frequency (%) for a randomly mating
population
Homozygous for allele 1 = p • p = p2
Homozygous for allele 2 = q • q = q2
Heterozygous = p • q or q • p = 2pq
2
p
+ 2pq +
2
q
=1
Hardy-Weinberg Lab
• Instructions dictate initial allele frequencies of:
– p = 0.5
– q = 0.5
• If there are 28 Teddy Grahams in your
population, how many should be pp?
pq? qq?
• Explain how you determined your
answer.
Teddy Grahams mate
randomly. All bears are
equally attractive.
Though they live a good life, it
is short. After having 2 babies,
they
die keeping the
.
population size constant
All bears are equally in danger
of predation due to their
yumminess
Teddy Graham Genetics
• Today you will be helping Teddy Grahams to
procreate.
• Reminder of the genetic rules:
– When honey and honey mate, 2
Honey are born
– When honey and chocolate mate,
2 speckled are born
– When honey and speckled mate,
One honey and one speckled are born
– When chocolate and speckled mate,
One chocolate and one speckled are born
When Speckled and Speckled mate
• Use the allele cards. Each speckled has a p and a
q allele
• Pick one allele for each parent to give
• This determines the genes of the first offspring
• Return the cards to the parent and pick again for
the second offspring
• Allow 5 generations to mate.
• Fill in the data chart and calculate allele
frequencies at the end of 5 generations
• Conduct a Chi Square test to see whether the
number of bears of each type you expect to
have if allele frequencies did not change,
differs from the observed (actual) number of
each type you have