Introduction to Genetic Analysis 651

Introduction to Genetic Analysis 651 - 44200_20_p643-678...

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Gene number and quantitative traits Continuous variation in a character is sometimes as- sumed to be necessarily caused by a large number of segregating genes, and so continuous variation is taken as “quantitative” character has been converted into a “quali- tative” one. This conversion has been accomplished by Fnding a way to make the difference between the means of the genotypes large compared with the variation within genotypes. MESSAGE A quantitative character is one for which the average phenotypic differences between genotypes are small compared with the variation between individuals within genotypes. evidence that a character is controlled by many genes. This multiple-factor hypothesis (that large numbers of genes, each with a small effect, are segregating to pro- duce quantitative variation) has long been the basic model of quantitative genetics, but, as we have just shown, this hypothesis is not necessarily true. If the dif- ference between genotypic means is small compared with the environmental variance, then even a simple
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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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