Development of an Ovine Genome Map with Emphasis on In Situ Hybridization

Livestock genome maps are used to identify economic trait loci and loci proximal to genes affecting economically important traits. This research contributes to the development of the ovine genome map by establishing techniques to physically map large DNA inserts to ovine chromosomes using fluorescent in situ hybridization. Fluorescent in situ hybridization techniques were established using yeast artificial chromosomes as DNA probes. Probes were as large as 1,000,000 kilobases and hybridized to fixed ovine metaphase chromosomes from a callipyge ewe. Three yeast artificial chromosome probes contained a genetic marker for the ovine callipyge gene. Probes were assigned to ovine chromosome pair 18, which was distinguished by a fluorescent R-band pattern. This method verified the location of the marker, which had previously been assigned to chromosome 18 through linkage analysis. This study also determined whether a chromosomal alteration is the cause of the callipyge phenotype, an economically advantageous trait where muscle mass is increased and fat deposition is decreased. A fibroblast cell line was produced from a six-month-old callipyge ewe. Chromosomes were examined using G and R dynamic banding techniques. The ewe had a normal diploid chromosome number of 54, and the karyotype consisted of 3 pairs of submetacentric chromosomes, 23 pairs of acrocentric autosomes, and 2 large acrocentric X chromosomes. G and R banding did not reveal any chromosomal structural abnormalities at the level of resolution (premetaphase) used in this study