FISH mapping and identification of canine chromosomes

The karyotype of the domestic dog (Canis familiaris) is widely accepted as one of the most difficult mammalian karyotypes to work with. The dog has a total of 78 chromosomes; all 76 autosomes are acrocentric in morphology and show only a gradual decrease in length. Standardization of the canine kary otype has been performed in two stages. The first stage dealt only with chr omosomes 1-21 which can be readily identified by conventional G-banding tec hniques, The remaining 17 autosomal pairs have proven to be very difficult to reliably identify by banding alone. To facilitate the identification of all canine chromosomes, chromosome-specific paint probes have been produced by DOP-PCR from flow-sorted dog chromosomes. Each paint probe has been use d for FISH to identify the corresponding chromosome(s), allowing precise id entification of all 78 canine chromosomes. The identification of the undesi gnated 17 autosomal pairs has been agreed upon by the standardization commi ttee during the second stage of their role. Cosmid clones containing micros atellite markers may now be conclusively assigned to their chromosomal orig in by simultaneous dual-color FISH with the corresponding paint probe. In t his way a collection of chromosome-specific cosmid clones is being construc ted, comprising at least one marker per chromosome, which will allow anchor ing of existing and future linkage groups to the physical map.