One of the larger contiguous blocks of mouse-human genomic homology includes the proximal portion of mouse chromosome 7 and the long arm of human chromosome 19. Previous studies have demonstrated the close relationship between the two regions, but have also indicated significant rearrangements in the relative orders of homologous mouse and human genes. Here we present the genetic locations of the homologs of 42 human chromosome 19q markers in the mouse, with an emphasis on genes also included in the human chromosome 19 physical map. Our results demonstrate that despite an overall inversion of sequences relative to the centromere, apparent 'transpositions' of three gene-rich segments, and a local inversion of markers mapping near the 19q telomere, gene content, order, and spacing are remarkably well conserved throughout the lengths of these related mouse and human regions. Although most human 19q markers have remained genetically linked in mouse, one small human segment forms a separate region of homology between human chromosome 19q and mouse chromosome 17. Three of the four rearrangements of mouse versus human 19q sequences involve segments that are located directly adjacent to each other in 19q13.3-q13.4, suggesting either the coincident occurrence of these events or their common association with unstable DNA sequences. These data permit an unusually in-depth examination of this large region of mouse- human genomic homology and provide an important new tool to aid in the mapping of genes and associated phenotypes in both species.
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