Introduction to Genetic Analysis 133

Introduction to Genetic Analysis 133 - 44200_04_p115-150...

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132 Chapter 4 Eukaryote Chromosome Mapping by Recombination Hence we might assert that if the allele pairs of the di- hybrid are assorting independently, there should be a 1:1:1:1 ratio of gametic types. Therefore it seems rea- sonable to use 1/4 of 500, or 125, as the expected pro- portion of each gametic class. However, note that the 1:1:1:1 ratio is expected only if all genotypes are equally viable. It is often the case that genotypes are not equally viable because individuals that carry certain alleles do not survive to adulthood. Therefore instead of alleles ratios of 0.5:0.5, used above, we might see (for example) ratios of 0.6 A :0.4 a, or 0.45 B :0.55 b . We should use these ratios in our predictions of independence. Let’s arrange the observed genotypic classes in a grid to reveal the allele proportions more clearly. to apply an objective statistical test that can support or not support one’s intuitive feeling. The x 2 test, which we encountered Frst in Chapter 2, provides a useful way of deciding if two genes are linked. How is the
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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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