Fine mapping of the polled locus to a 1-Mb region on bovine chromosome 1q12.

The absence of horns in Bos taurus is under genetic control of the autosomal dominant polled locus which has been genetically mapped to the centromeric region of cattle Chromosome 1. Recently a 4-Mb BAC contig of this chromosomal region has been constructed. Toward positional cloning of the bovine polled locus, we identified 20 additional microsatellite markers spread over the contig map by random sequencing of bacterial artificial chromosome (BAC) subclones. A total of 26 markers were genotyped in 30 two-generation half-sib families of six different German cattle breeds segregating for the hornless phenotype including 336 informative meioses for the polled character. Our fine-mapping study involving 19 recombinant haplotypes allowed us to narrow the critical region for the bovine polled locus to a 1-Mb segment with a centromeric boundary at RP42-218J17_MS1 and a telomeric boundary at BM6438. For marker-assisted selection purposes, the first evidence of informative flanking markers helps to predict polled genotypes with a higher degree of accuracy within families until testing of the causative mutation is available.