Multispecies alignments to human chromosomes. Shown are the multispecies alignments of human chromosomes (a) 7 and (b) 12. Red bars represent the homology synteny blocks (HSBs) in the seven eutherian species that were compared in our analyses. Black bars represent the regions of homology to the chicken genome . Segments 7a (red), 7b (blue), 12a (green), and 12b (pink) are portions of human chromosomes comprising the ancestral eutherian karyotype [8,22]. The location of human fragile sites (FRA) is given to the left of the ideogram of each human chromosome: red for common fragile sites and blue for rare fragile sites. The distribution of tandem repeats along these human chromosomes is shown on the extreme right. The high concentrations of tandem repeats in the pericentromeric and telomeric areas of each chromosome have been the omitted to provide clearer resolution of the distribution of repeats elsewhere on the chromosomes (see text for details).