Introduction to Genetic Analysis 656

Introduction to Genetic Analysis 656 - 44200_20_p643-678...

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fundamental to distinguish familiality from heritability. Character states are familial if members of the same family have them in common, for whatever reason. They are heritable only if the similarity arises from having genotypes in common. There are two general methods for establishing the heritability of a trait as distinct from its familiality. The first depends on phenotypic similarity between relatives. For most of the history of genetics, this method has been the only one available, and so nearly all the evi- dence about heritability for most traits in experimental organisms and in humans has been established by using this approach. The second method, using marker-gene segregation, depends on showing that genotypes carry- ing different alleles of certain marker genes also differ in their average phenotype for a quantitative character. If the marker genes (which have nothing to do with the character under study) are seen to vary in relation to the character, then presumably they are linked to genes that do influence the character and its variation. Thus, heritability is demonstrated even if the actual genes causing the variation in the character are not known. This method requires that the organism being studied have large numbers of detectable, genetically variable marker loci spread throughout its genome. Such marker loci can be observed through variants in DNA sequence, electrophoretic studies of protein variation or, in vertebrates, immunological studies of blood-
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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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