Huntington's disease is an inherited neurological ailment with a variable age of onset (see Chapter 22). A protein called huntingtin has a sequence of repeated glutamine residues, all encoded by CAG. Te number of repeated CAG triplets is expanded in Huntington's disease, apparently as the result of replication errors. Te age of onset is related to the number of CAG triplets in the repeat region; the more glutamine codons, the earlier the onset. Describe experimental evidence, using Southern blotting, that is consistent with this finding.