Huntington’s disease is a hereditary central nervous system disorder characterized by tandem repeats of the sequence 5′-CAG-3′ in the gene that encodes a protein called huntingtin. The disease is progressive from generation to generation, meaning that in later generations the number of CAG repeats increases and the age of onset of symptoms decreases. Refer to Figure 21.4 and describe the sort of evidence supporting the generational increase in the number of CAG repeats. Note: This will be different from the kind of evidence asked for in problem 8..

Figure 21.4

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+ Bottom Satellite DNA CAG repeat 67% G + C A260 Chromosomal DNA (human) 41% G + C Shear during DNA Isolation Centrifuge to equilibrlum in CSCI Density Top