Introduction to Genetic Analysis 129

Introduction to Genetic Analysis 129 - 128 Chapter 4...

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Unformatted text preview: 128 Chapter 4 Eukaryote Chromosome Mapping by Recombination heterozygote for mapping analysis. In the early years of building genetic maps, the markers were genes with vari- ant alleles producing detectably different phenotypes. As organisms became more intensively studied, a larger range of mutant alleles was found and hence larger numbers of genes could be used as markers for mapping studies. However, even when maps appeared to be full of loci of known phenotypic effect, measurements showed that those genes were separated by vast amounts of DNA. These gaps could not be mapped by linkage analysis, be- cause no phenotypes had been matched to genes in those regions. Large numbers of additional genetic markers were needed that could be used to fill in the gaps to pro- vide a higher-resolution map. The discovery of various kinds of molecular markers provided a solution. A molecular marker is a site of heterozygosity for some type of DNA change not associated with any mea- surable phenotypic change. These are called silent changes. Such a heterozygous site can be mapped by linkage analysis just as a conventional heterozygous al- lele pair can be. Because molecular markers can be easily detected and are so numerous in a genome, when...
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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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