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genotype has some relative probability of survival. This
general calculation is shown in Box 195. After one gen
eration of selection, the new value of the frequency of
A
is equal to the old value (
p
) multiplied by the ratio of
the mean Ftness of
A
alleles,
, to the mean Ftness of
the whole population,
. If the Ftness of
A
alleles is
W
W
A
greater than the average Ftness of all alleles, then
is greater than unity and
p
9
is larger than
p.
Thus, the al
lele
A
increases in the population. Conversely, if
is less than unity,
A
decreases. But the mean Ftness of the
population (
) is the average Ftness of the
A
alleles and
of the
a
alleles. So if
is greater than the mean Ftness
W
A
W
W
A
/
W
W
A
/
W
632
Chapter 19
•
Population Genetics
The Effect of Selection on Allele Frequencies
BOX 195
Suppose that a population is mating at random with
respect to a given locus with two alleles and that the
population is so large that (for the moment) we can
ignore inbreeding. Just after the eggs have been fertil
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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

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