Five Charolais families known to segregate for both horned and polled were selected and tested for linkage analysis by use of microsatellites and karyotyping for Robertsonian translocation 1;29. No recombinants were found between any of these markers and the polled phenotype or each other. When statistical analysis was performed, the logarithm of the odds (LOD) indicated that there was 100% linkage occurring between the markers and the phenotype (p < 0.001). These microsatellite markers, TGLA49 and BM6438, can be assumed to be very close to the actual gene that determines the polled phenotype. Another linked marker, SOD1, was physically mapped, which places all of these markers within 1 q 12-14, very near the centromere of Chromosome (Chr) 1. A homozygous polled cow was identified in this study by following the alleles at both markers and the phenotypes in her family.
which can serve as a third marker to test for recombination with the centromere.
Methods
Cattle. Three of the families were obtained from a purebred Charolais herd in Alberta, while the other two families were obtained from a herd in Saskatchewan. Each family was composed of paternal half or full siblings. All of the cattle were produced via artificial insemination and/or embryo transfer in both herds. Families were chosen for this analysis because bulls heterozygous for polled were bred to homed cows and produced at least five calves, some of which were horned and some polled. Dams were available in most cases and were sampled whenever possible. Blood was drawn in vacutainers containing EDTA from animals at these ranches. Semen was used for several of the sires.