Introduction to Genetic Analysis 667

Introduction to Genetic Analysis 667 - 44200_20_p643-678...

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666 Chapter 20 Quantitative Genetics together, and the different marker genotypes in the F 2 or backcross will have different average phenotypes for the quantitative character. Quantitative linkage analysis The localization of QTLs to small regions within chro- mosomes requires the presence of closely spaced marker loci along the chromosome. Moreover, it must be possi- ble to create parental lines that differ from each other in the alleles carried at these marker loci. With the advent of molecular techniques that can detect genetic poly- morphism at the DNA level, a very high density of vari- ant loci has been discovered along the chromosomes of all species. Especially useful are restriction fragment length polymorphisms (RFLPs), tandem repeats, and sin- gle nucleotide polymorphisms (SNPs) in DNA. Such polymorphisms are so common that any two lines se- lected for a difference in quantitative traits are also sure to differ from each other at some known molecular marker loci spaced a few crossover units from each other along each chromosome. An experimental protocol for localizing genes, shown in Figure 20-16, uses groups of individuals that differ markedly in the quantitative character of interest as well as at marker loci. These groups may be created
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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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