A male linkage map of the cattle (Bos taurus) genome was constructed using nine large half-sib families. The map consists of 269 loci, of which 249 are microsatellites and 20 are structural genes. Among the 249 microsatellites, 140 are markers selected from other maps and 98 are new assignments. Chromosome assignment were established for 35 new markers by somatic cell hybrid analysis, of which 26 were confirmed by linkage analysis. Genome coverage is 1975 cM contained within terminal markers on all 29 autosomes. The average distance between adjacent loci is 9.7 cM, with 72.1% of the map intervals < or = 15 cM and 4.9% of the intervals > or = 25 cM. The inclusion of mapped markers permitted integration and comparisons with other maps, facilitating the identification of discrepancies in chromosome assignment, gene order, and map distance. The inclusion of Type I and blood group markers in the map was useful for comparative mapping, revealing possible blood group orthologies between humans and cattle. The map generated will serve as a useful tool for comparative mapping, mapping of quantitative trait loci and marker assisted selection.

In total, 82 ESTs were generated from 51 unique clones randomly selected from a cattle ovary cDNA library. Among these clones, 22 (42.1%) had 5' and/or 3' ends that matched with known human or other mammalian coding sequences, 18 (35.3%) matched human or other ESTs, and 11 (21.6%) represented novel transcripts with no significant match to any sequence in the databases. The relatively high frequency of ESTs with no matches in GenBank or dbEST indicates that bovine ovary may be a source of novel candidate genes for loci affecting cattle reproduction traits. Primers were designed for 11 ESTs that had human orthologs in GenBank. These ESTs were mapped to 10 bovine autosomes by PCR screening of a somatic cell hybrid panel. Among these 11 ESTs, 4 corresponded to genes previously mapped in humans and had chromosome assignments on the bovine map that were consistent with available comparative mapping data. Although the human orthologs of the remaining 7 mapped bovine ESTs have not been mapped, the human map location could be predicted on the basis of existing comparative mapping data. Because of the general utility of our approach for comparative genome analysis, we have termed it comparative mapping by annotation and sequence similarity (COMPASS). With the cost of large-scale EST sequencing becoming more affordable, and the rapid expansion of DNA databases, it is likely that COMPASS will be a preferred strategy for high throughput comparative mapping.

Summary A small‐insert bovine genomic library was constructed in pBluescript II SK(+) and enriched for microsatellites by selective rescue of single‐stranded pBluescript DNA carrying (CA)n/(TG) n tandem repeats. Approximately 50% of the clones in the enriched library contained (CA) nrepeats or CA‐rich sequences. Sequencing of clones selected for (CA) n repeats resulted in the identification and characterization of 45 (CA) npolymorphic microsatellites. Genotyping in 9 large paternal half‐sib families indicated that 40 of these microsatellite markers exhibit autosomal Mendelian inheritance. The numbers of alleles range from 2 to 18, with an average of 6‐3 per locus. The polymorphic microsatellite markers we have identified and characterized will contribute to the construction of a high‐resolution linkage map of bovine genome.

SummaryA report of the first workshop on the genetic map of bovine chromosome 23 (BTA23) is given. Five laboratories contributed data from 29 loci, including a total 11586 informative genotypes. The combined pedigrees represented 1930 potentially informative meioses. Eighteen of the 29 loci were common to two or more data sets and were used to construct a framework linkage map of BTA23. Twelve of the 18 could be ordered on the linkage map with a likelihood ratio of greater than 100O:l. Thus, a low resolution consensus map was constructed with a high level of support for order. The sex-averaged, female and male maps span 54.5, 52.7 and 55.8 cM, respectively. Sex-specific differences in recombination frequency were identified for eight pairs of framework loci. Average genetic distance between framework loci on the sex-averaged map is 5.0 cM.