Introduction to Genetic Analysis 117

Introduction to Genetic Analysis 117 - and color assorted...

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116 Chapter 4 Eukaryote Chromosome Mapping by Recombination CHAPTER OVERVIEW T his chapter is about using crossing analysis to map the positions of genes on chromosomes. The map po- sition of a gene is a key piece of information that is re- quired to analyze its function. You might suppose that the sequencing of complete genomes has made crossing analysis redundant because such sequencing reveals genes and their positions on the chromosome. However, most of the genes identified by sequencing are of un- known function, and their impact on the organism is not understood. Hence the gene as identified by phenotypic analysis must be tied to the gene as identified by se- quencing. This is where chromosome maps are crucial. Mendel’s experiments showed that allele pairs for genes influencing different pea characters such as size
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Unformatted text preview: and color assorted independently, giving rise to precise ratios of progeny. To explain independent assortment, we noted that the genes inuencing color and texture resided on different chromosomes, and that different chromosome pairs behave independently at meiosis. But what happens when allele pairs of different genes are on Unseen distribution of crossovers Meiocyte 1 A a B b Few recombinants Short map distance Numerous recombinants Long map distance C c locus locus locus Meiocyte 2 Meiocyte 3 Meiocyte 4 etc. Chromosome map CHAPTER OVERVIEW Figure Figure 4-1 Crossovers produce recombinant chromatids whose frequency can be used to map genes on a chromosome. 44200_04_p115-150 3/4/04 10:36 AM Page 116...
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