Introduction to Genetic Analysis 660

Introduction to Genetic Analysis 660 - 44200_20_p643-678...

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First, we can see that the scores of the children have a high correlation with those of their biological parents but a low correlation with those of their adoptive par- ents. In fact, in our hypothetical example, the correlation 20.7 Quantifying heritability 659 population, then H 2 estimates how much phenotypic variation will still be present. So, if the heritability of per- formance on an IQ test were found to be, say, 0.4, then we could predict that, if all children had the same devel- opmental and social environment as the “average child,” about 60 percent of the variation in IQ test performance would disappear and 40 percent would remain. The requirement that the new constant environ- ment be at the mean of the old environmental distribu- tion is absolutely essential to this prediction. If the envi- ronment is shifted toward one end or the other of the environmental distribution present in the population used to determine H 2 or if a new environment is intro- duced, nothing at all can be predicted. In the example of IQ test performance, the heritability gives us no infor- mation at all about how variable performance would be if the developmental and social environments of all chil- dren were enriched. To understand why this is so, we must return to the concept of the norm of reaction. The separation of phenotypic variance into genetic
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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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