Sequence similarity between three homologous human/mouse genomic regions, which diverged at different evolutionary rates. (a) ERCC2 locus (Accession nos. L47234; L47235). (b) MHC-II region (Accession nos. X87344; AF100956, AF027865). (c) HOX cluster (Accession nos. AC009336; L1084). Abscissa: sequence position along the human sequence. Ordinate: sequence position along the mouse sequence (upper panels) and identity of locally aligned fragments (middle panels). For better illustration, the lowerpanels show a sliding-window-plot of the identity. The position of exons is indicated by grey vertical lines. Note that the HOX cluster is highly conserved also in intronic and intergenic parts of the sequence.