To enhance the comparative map for human Chromosome (Chr) 13, we identified clones for human genes and anonymous loci that cross-hybridized with their mouse homologs and then used linkage crosses for mapping. Of the clones for four genes and twelve anonymous loci tested, cross-hybridization was found for six, COL4A1, COIAA2, D13S26, D13S35, F10, and PCCA. Strong evidence for homology was found for COL4A1, COIAA2, D13S26, D13S35, and F10, but only circumstantial homology evidence was obtained for PCCA. To genetically map these mouse homologs (CflO, Col4al, Col4a2, D14H13S26, D8H13S35, and Pcca-rs), we used interspecific and intersubspecific mapping panels. D14H13S26 and Pcca-rs were located on the distal portion of mouse Chr 14 extending by -30 cM the conserved linkage between human Chr 13 and mouse Chr 14, assuming that Pcca-rs is the mouse homolog of PCCA. By contrast, CflO, Col4aI, Col4a2, and D8H13S35 mapped near the centromere of mouse Chr 8, defining a new conserved linkage. Finally, we identified either a closely linked sequence related to Col4a2, or a recombination hot-spot between Col4al and Col4a2 that has been conserved in humans and mice.
order and relative distances inferred from genetic maps (Kingsmore et al. 1989;Oakey et al. 1992).
Although progress in the development of the comparative map has been considerable with the number of markers in the map doubling the past 30 months, substantial portions of the genome remain poorly defined. An example is the suspected homology between the central-distal portion of human Chr 13 and the centraldistal portion of mouse Chr 14 (Nadeau et al. 1992; Copeland et al., 1993b). This suspicion is based on the presence of small clusters of homologous genes that flank both of these chromosome segments (Nadeau et al. 1995). To enhance the comparative map for human Chr 13, we identified and genetically mapped mouse homologs for four human genes and two anonymous DNA loci. Not only were we able to extend the conserved linkage involving human Chr 13 and mouse Chr 14, we identified a new conserved linkage involving human Chr 13 and mouse Chr 8, and found either a new pseudogene or a recombination hot-spot that has been conserved in the two species.