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What is the Hardy-Weinberg
The principle states that allele and
genotype frequencies in a population
will remain constant from generation
to generation in the absence of other
evolutionary influences.
5 principles of theorem:
1. Population is large
2. Matings are random
3. There are no net changes in the gene pool
due to mutation
4. No migration
5. No selection= equal reproductive success
Important Terms
Natural Selection
Gene Pool
What are allele frequencies?
• Because there are only two alleles in this case,
the frequency of one plus the frequency of the
other must equal 100%, which is to
• where p= A and q= a
• Frequency of the diploid combinations
– p2 + 2pq + q2 = 1
• p2 is AA
• 2pq is Aa, and
• q2 is aa
The purpose of Hardy-Weinberg
• Scientists can investigate the roles of mutation,
migration, population size, nonrandom mating,
and natural selection effecting evolutionary
• Some populations maintain genetic equilibrium
• The principle describes an ideal condition against
which the effects of these influences can be
• Allele frequencies will remain unaltered
indefinitely unless evolutionary mechanisms such
as mutation and natural selection cause them to
Example Problem:
1.You calculate that you have
16% homozygous recessive bears (happy) or q2 =
20% or .20, by taking the square root q = .45
(2 out 10 bears were happy)
2. p + .45 = 1, so p = .55
• .45 + .55 = 1 or 40% + 60% = 100%
3. Solve for p2 by .55 x .55 = .30
4. Then solve for 2pq = 2 x .45 x .55= .50
5. So you data would show, AA=.30, Aa=.50, and
Let’s practice:
• Pull a random population of 10 teddy grahams from
the den
• How many homozygous recessive bears do you have?
(happy) That would be q2 because % of population.
– Make sure to convert to a decimal value to fill it in table
• Take the Square root of q2 to give you q
• You can then solve for p by using the formula p + q = 1
• Solve for p2 squaring p
• Solve for 2pq by taking 2 x p x q =
• Check out another example on you tube:
Complete your lab!
• Fill in your data table
• Your generations should increase 10, 14, 18,
• Answer the questions on looseleaf on the
bottom of your lab.
• For the question asking about eating sad
bears- run 2 rounds to see what would
happen to p?
On your OWN!
• 18% of the bear population is happy. Happy is
the recessive trait in the bear population.
1. What is the percent of individuals in the
population that are dominant?
2. What is the frequency of dominant and
recessive alleles?
3. What is the percentage of the population
that is heterozygous for the trait?