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equal to the square of the frequency of the allele. The
frequency of heterozygotes for a particular pair of alleles
is twice the product of the frequency of those two al
leles. For example, suppose there are three alleles,
A
1
,
A
2
, and
A
3
, whose frequencies are .5, .3, and .2, respec
tively. Then the HardyWeinberg equilibrium frequen
cies of the homozygotes would be
A
1
A
1
A
2
A
2
A
3
A
3
(.5)
2
5
.25
(.3)
2
5
.09
(.2)
2
5
.04
and the frequencies of the heterozygotes would be
A
1
A
2
A
1
A
3
A
2
A
3
2(.5)(.3)
5
.30
2(.5)(.2)
5
.20
2(.3)(.2)
5
.12
Heterozygosity
A measure of genetic variation (in contrast with its
de
scription
by allele frequencies) is the amount of
hetero
zygosity
for a gene in a population, which is given by the
total frequency of heterozygotes for the gene. This het
erozygosity either can be directly observed by counting
heterozygotes or it can be calculated from the allele fre
quencies, using the HardyWeinberg equilibrium propor
tions. If one allele is in very high frequency and all oth
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.
 Spring '08
 JOHNSON
 Biology, Reproduction

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