Introduction to Genetic Analysis 661

Introduction to Genetic Analysis 661 - 44200_20_p643-678...

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to the amount of active gene product, we would expect the heterozygote phenotype to be exactly intermediate between the homozygotes (show no dominance). For many quantitative traits, however, neither of these simple cases is the rule. In general, heterozygotes are not exactly intermediate between the two homozy- gotes but are closer to one or the other (show partial dominance), even though there is an equal mixture of the primary products of the two alleles in the heterozy- gote. Suppose that two alleles, a and A, segregate at a lo- cus in±uencing height. In the environments encountered by the population, the mean phenotypes (heights) and frequencies of the three genotypes might be: of children with biological parents is r 5 1.00, but with adoptive parents it is r 5 0. (Remember that a correla- tion between two sets of numbers does not mean that the two sets are identical, but that, for each unit of in- crease in one set, there is a constant proportional in- crease in the other set—see the Statistical Appendix on statistical analysis at the end of this chapter.) This per- fect correlation with biological parents and zero correla- tion with adoptive parents means that H 2 5 1, given the arguments just developed. All the variation in IQ
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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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