Huntington\'s disease is an inherited neurological ailment with a variable age o

Question

Huntington's disease is an inherited neurological ailment with a variable age of onset. A protein called huntingtin has a sequence of repeated glutamine residues, all encoded by CAG. The number of repeated CAG triplets is expanded in Huntington's disease, apparently as the result of replication errors. The 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.

From the human genome sequence, select _____________ enzymes that will bracket the region of the huntingtin gene that contains the triplet repeat. Obtain DNA from members of families afflicted with Huntington's disease. Carry out Southern blotting with the selected____________ enzymes. Probe each blot with an oligonucleotide (____________ )n or its complement ____________( )n. Or PCR amplify the region of interest and run gel electrophoresis to estimate, from the size of the repeat fragment, the number of repeats; this is what is actually done in HD testing. The age of onset should correlate______________ with the size of the gel band detected by the probe; the larger the band, the ___________ the age of onset.

(Word bank below)

GTC

positively

CAG

restriction

ligation

younger

negatively

older

From the human genome sequence, select _____________ enzymes that will bracket the region of the huntingtin gene that contains the triplet repeat. Obtain DNA from members of families afflicted with Huntington's disease. Carry out Southern blotting with the selected____________ enzymes. Probe each blot with an oligonucleotide (____________ )n or its complement ____________( )n. Or PCR amplify the region of interest and run gel electrophoresis to estimate, from the size of the repeat fragment, the number of repeats; this is what is actually done in HD testing. The age of onset should correlate______________ with the size of the gel band detected by the probe; the larger the band, the ___________ the age of onset.

(Word bank below)

GTC

positively

CAG

restriction

ligation

younger

negatively

older

Explanation / Answer

From the human genome sequence, select restriction enzymes that will bracket the region of the huntingtin gene that contains the triplet repeat. Obtain DNA from members of families afflicted with Huntington's disease. Carry out Southern blotting with the selected restriction enzymes. Probe each blot with an oligonucleotide (CAG)n or its complement (GTC)n. Or PCR amplify the region of interest and run gel electrophoresis to estimate, from the size of the repeat fragment, the number of repeats; this is what is actually done in HD testing. The age of onset should correlate negagtively with the size of the gel band detected by the probe; the larger the band, the younger the age of onset.

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