Introduction to Genetic Analysis 87

Introduction to Genetic Analysis 87 - 86 Chapter 3 The...

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Unformatted text preview: 86 Chapter 3 The Chromosomal Basis of Inheritance TELOMERES Telomeres are the ends of chromosomes. Generally there is no visible structure that represents the telomere, but at the DNA level it can be distin- guished by the presence of distinct nucleotide se- quences. The ends of chromosomes represent a special challenge to the chromosomal replication mechanism, and this problem is overcome by the presence at the tips of chromosomes of tandem arrays of simple DNA se- quences that do not encode an RNA or a protein prod- uct. For example, in the ciliate Tetrahymena there is rep- etition of the sequence TTGGGG, and in humans the repeated sequence is TTAGGG. Chapter 7 will explain how the telomeric repeats solve the problem of replicat- ing the ends of linear DNA molecules. Binding of a telomere probe is shown in Figure 3-16. BANDING PATTERNS Special chromosome-staining procedures have revealed sets of intricate bands (trans- verse stripes) in many different organisms. The positions and sizes of the...
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