Use of cosmid-derived and chromosome-specific canine microsatellites.

The majority of microsatellite markers being used to generate the emerging genetic linkage maps of the dog are derived from small-insert, random clones. While such markers are easy to generate, they have the disadvantage that they cannot easily be physically mapped by fluorescence in situ hybridization (FISH), making it difficult to assess the extent of genome coverage represented by such maps. In contrast, microsatellite markers from large-insert libraries enable the linkage groups within which they fall to be physically anchored to specific chromosomes. One aim of our work is to identify at least one microsatellite-containing cosmid clone for each canine chromosome, to ensure that linkage groups exist for all chromosomes. This is particularly important for a species with as complex a karyotype as the dog. Locating two cosmids on each chromosome would allow the orientation of the linkage groups to be established. Chromosomal locations of cosmid clones containing microsatellites have been determined by FISH and confirmed using canine chromosome-specific paints. Microsatellite sequences have been genotyped on the DogMap reference family. Microsatellites derived from flow-sorted, chromosome-specific libraries represent another source of useful markers. Initial studies have been carried out on the canine X chromosome, on which markers were underrepresented in our initial studies.