Comparative karyotype of rat and mouse using bidirectional chromosome painting

A comparative karyotype of rat (Rattus norvegicus) and mouse (Mus musculus) based on chromosome G-banding morphology, heterologous chromosome painting results and available gene mapping data is proposed. Whole chromosome pain ting probes from both species were generated by PARM-PCR amplification of f low sorted chromosomes. Bidirectional chromosome painting identifies 36 seg ments of syntenic homology and allows us to propose a nearly complete compa rative karyotype of mouse and rat (except for RNO 13 p and RNO 19 p12-13). Seven segments completely covered the RNO chromosomes 3, 5, 8, 11, 12, 15 a nd 18. Eight segments completely covered the MMU chromosomes 3, 4, 6, 7, 9, 12, 18 and 19. The RNO chromosomes 5, 8, 18 show complete homology with th e MMU chromosomes 4, 9 and 18, respectively. Bidirectional hybridization re sults clearly assign 16 segments to subchromosomal regions in both species. Interpretation of the results allows subchromosomal assignment of all the remaining segments apart from seven distributed on chromosomes MMU 15, MMU 10 B2-D3 and MMU 17 E3-E5. The proposed comparative karyotype shows overall agreement with available comparative mapping data. The proposed repartitio n of syntenic homologous segments between the two species provides useful d ata for gene-mapping studies. In addition, these results will enable the re construction of the karyotype of the Cricetidae and Muridae common ancestor and the definition of the precise rearrangements which have occurred in bo th mouse and rat lineages during evolution.