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Hardy-Weinberg Principle
Last day we left off talking about
populations…
 Populations geneticists are able to quantify
the total number of alleles within a population
==this is known as the gene pool
 They are able to accomplish this by
measuring each allele frequency, which is the
proportion of gene copies in a population for a
given allele
 Therefore evolutionary changes in
populations can be quantitatively measured by
looking for changes in allele frequencies

In terms of evolution, would the
dominant form of a moth wing become
more and more common over time?
 Do allele frequencies remain constant or
change over time?
 These questions were answered
independently (think Darwin vs. Wallace) by
a mathematician named Hardy and physicist
named Weinberg== thus Hardy-Weinberg
principle

Allele frequencies will not change over time
(generation-generation) if the following conditions
are met:
I. The population is very large
II. Mating opportunities are equal
III. No mutations occur
IV. No migration occurs
V. All individuals have an equal chance at
reproductive success==no natural selection

The H-W-P is often expressed using the following
equation (for a gene with only 2 alleles==A/a):
 let p=frequency of A and q=frequency of a, then
p+q=1
(p+q)2= 1
p2 + 2pq + q2 = 1, where

p2 = frequency of AA; 2pq= frequency of Aa; and q2 =
frequency of aa
Note: genotype frequencies will remain the same from generation to
generation as long mating is random
Pgs 547-549
Pg 549 PP’s #1-3
Quiz Tomorrow
-self quiz
-review #1-4, 7, 8, 10, 15