Figure 1.

Hairpin-induced trinucleotide repeat instability. The TNR is indicated by gray lines, flanking DNA by black lines. (a) Nascent-strand hairpin formation results in over-replication of a segment of the TNR in one chromatid. A second round of replication of the hairpin strand fixes the expanded allele in the genome. (b) Template-strand hairpin formation results in under-replication of a segment of the TNR in one chromatid. A second round of replication of the nonhairpin strand fixes the contracted allele in the genome. (Reprinted from [7] with permission)