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Biology 30: Populations and Communities
Hardy-Weinberg
Gene pool – the various alleles of all the genes in all the
members of a population.
Evolution occurs when there is a change in the allele frequency
in a gene pool.
 Individuals do not evolve, only populations do.
Genetic Equilibrium – the frequency of a given allele remains
stable, one generation after the next, thus no evolution.
Conditions of the Hardy-Weinberg Principle
Allele frequencies in a population will not change if:
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The population is infinitely large
No migration occurs
No mutations occur
No natural selection occurs
Mating is random
Hardy-Weinberg (HW) principle measures change in allele frequencies in a gene pool.
 Therefore it can be used to demonstrate the evolution of a single trait.
Formulas:
p+q=1
Symbols:
(not on data booklet)
p2 + 2pq + q2 = 1 (on data booklet)
p = dominant allele (gene frequency, allele frequency)
q = recessive allele (gene frequency, allele frequency)
p2 = AA genotype
Dominant phenotype (cannot use this in HW
calcs, p & q are both unknown)
2pq = Aa genotype
q2 = aa genotype or recessive phenotype
Example Questions
1. A large population consists of 400 individuals, of which 289 are MM, 102 are Mm, and 9 are mm.
Determine the allele frequencies for M and m.
2. If 1 in 400 people in a large population have a recessive disorder determine the proportion of individuals
who are carriers of this disorder.
3. The gene frequency for free earlobes, which is the dominant trait, is 0.63. What is
the frequency of individuals who have attached earlobes in the population?
Hardy-Weinberg
Tutorial
Key:
1. p = 0.85, q = 0.15
2. 38
3. 0.1369