Introduction to Genetic Analysis 624

Introduction to - 44200_19_p611-642 11:23 AM Page 623 19.2 Effect of sexual reproduction on variation 623 Heterozygosity 1.0 0.9 0.8 0.7 0.6 0.5

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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 Hardy-Weinberg 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 Hardy-Weinberg 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.

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