Introduction to Genetic Analysis 659

Introduction to Genetic Analysis 659 - correlation of 0.5,...

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Unformatted text preview: correlation of 0.5, then our estimate of heritability would be 0.4/0.5 5 0.8. But such an estimate fails to take into account the fact that the environments of sib- lings also may be correlated. Unless we are careful to raise the siblings in independent environments, our estimate of H 2 will be too large and could even exceed 1 if the observed phenotypic correlation were greater than 0.5. To get around this problem, we use the differences between phenotypic correlations of different relatives. For example, the difference in genetic correlation be- tween full and half-siblings is 1/2 2 1/4 5 1/4. Lets contrast this with their phenotypic correlations. If the environmental similarity is the same for half- and full siblingsa very important condition for estimating her- itabilitythen environmental similarities will cancel out if we take the difference in correlation between the two kinds of siblings. This difference in phenotypic cor- relation will then be proportional to how much of the variance is genetic. Thus: but and so an estimate of H 2 is: where the correlation here is the phenotypic correlation. This estimate, as well as others based on correlations between relatives, depends critically on the assumption that environmental correlations between individuals are...
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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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