Introduction to Genetic Analysis 85

Introduction to Genetic Analysis 85 - 44200_03_p73-114...

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84 Chapter 3 The Chromosomal Basis of Inheritance HETEROCHROMATIN The general material that collec- tively composes a chromosome is called chromatin by cytogeneticists. When chromosomes are treated with chemicals that react with DNA, such as Feulgen stain, distinct regions with different staining characteristics become visible. Densely staining regions are called heterochromatin; poorly staining regions are said to be euchromatin. The distinction is the result of the degree of compactness, or coiling, of the DNA in the chromo- some. The position of much of the heterochromatin on the chromosome is constant and is, in this sense, a hereditary feature. Look ahead to Figure 4-14 (page 000) for good examples of heterochromatin in tomato. Table 3-3 Human Chromosomes Diagrammatic Relative Centromeric Group Number representation length* index† Large chromosomes A1 8.4 48 (M) 2 8.0 39 3 6.8 47 (M) B4 6.3 29 5 6.1 29 Medium chromosomes C6 5.9 39 7 5.4 39 8 4.9 34 9 4.8 35 10 4.6 34 11 4.6 40 12 4.7 30 D1 3 3.7 17 (A) 14 3.6 19 (A) 15 3.5 20 (A) Small chromosomes E1 6 3.4
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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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