Figure 2.

(A) Small-pool PCR followed by Southern blot for analysis of CTG repeat length. DNA from fibroblast clones was diluted to produce, on average, one amplifiable expanded repeat allele per PCR tube. The repeat tract was amplified by 24 cycles of PCR. The amplified product was detected by Southern blot probed with a CAG repeat oligonucleotide. The scale on the left shows the molecular weight markers converted into numbers of CTG repeats. (B) Histograms showing repeat length distributions in MRC-5-800R clone A (conditional expression of expanded repeat). The distribution of unstable alleles is shown by gray bars (left vertical axis). The frequency of stable alleles is shown by black bars (right vertical axis). Allele lengths are grouped in bins spanning 50 repeats.