Introduction to Genetic Analysis 89

Introduction to Genetic Analysis 89 - 44200_03_p73-114...

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88 Chapter 3 The Chromosomal Basis of Inheritance centromeres of all four chromosome pairs. The chromo- center of Drosophila salivary gland chromosomes is shown in Figure 3-18b, in which the letters L and R stand for arbitrarily assigned left and right arms. Along the length of a polytene chromosome are transverse stripes called bands. Polytene bands are much more numerous than G bands, numbering in the hun- dreds on each chromosome (see Figure 3-18c). The bands differ in width and morphology, so the banding pattern of each chromosome is unique and characteristic of that chromosome. Recent molecular studies have shown that, in any chromosomal region of Drosophila, there are more genes than there are polytene bands, so there is not a one-to-one correspondence of bands and genes as was once believed. Another tool that is useful for distinguishing chromo- somes is to label them with speci±c tags that are joined to different colored ²uorescent dyes, a procedure called FISH (fuorescent in situ hybridization). This procedure was used to obtain the image in Figures 3-8 and 3-11. By using all the available chromosomal landmarks together,
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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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