DEVELOPMENT OF A BOVINE X-CHROMOSOME LINKAGE GROUP AND PAINTING PROBES TO ASSESS CATTLE, SHEEP, AND GOAT X-CHROMOSOME SEGMENT HOMOLOGIES

The X chromosome linkage group is conserved in placental mammals, Howe ver, X chromosome morphological differences, due to internal chromosom e rearrangements, exist among mammalian species, We have developed bov ine chromosome painting probes for Xp and Xq to assess segment homolog ies between the submetacentric bovine X chromosome and the acrocentric sheep and goat X chromosomes, These painting probes and their corresp onding DNA libraries were developed by chromosome micromanipulation, D NA micropurification, microcloning, and PCR amplification, The bovine Xp painting probe identified an interstitially located homologous segm ent in the sheep and goat Xq region, most probably resulting from chro mosome inversion. Ten type II (microsatellite) markers obtained from t he bovine Xq library and five other X chromosome assigned, but unlinke d, markers were used to generate a linkage map for Xq spanning 89.4 ce ntimorgans. The chromosome painting probes and molecular markers gener ated in this study would be useful for comparative mapping and tracing of internal X chromosome rearrangements in all ruminant species and w ould contribute to the understanding of mammalian sex chromosome evolu tion.