The poll and horn genes are located on Chromosome 1, the largest chromosome. Each animal has two genes which determine if they are polled or horned. The poll gene (P) is dominant and the horn gene (h) is recessive. An animal will be poll when it has two poll genes (homozygous or PP) or one poll gene and one horn gene (heterozygous or Ph). An animal will be horned if it carries two horn genes (hh). By looking at a poll animal you cannot tell if it is homozygous or heterozygous for the poll gene; this can only be determined by genetic testing. A heterozygous poll bull may throw horned calves if the dam also carries one or two horn genes.
How Purebred (poll) Bazadais are different from Fullblood (horned) Bazadais
Bazadais is a horned breed. Poll Bazadais have been developed by introducing the poll gene. This has been achieved by crossing Bazadais with a base breed that carries the poll gene. Poll calves (Ph) are retained and bred back to Bazadais for 4 to 5 generations. To obtain homozygous poll Bazadais (PP), two heterozygous poll animals (Ph) are crossed with 25% of the resulting calves being PP. The homozygous poll animal is homozygous for the poll gene from the base breed. The poll animal also has thousands of other Chromosome 1 genes from the base breed. These “non-Bazadais” genes are introduced with the poll genes. In homozygous poll Bazadais cattle there may be none or very few genes on Chromosome 1 that come from the Bazadais breed. Poll Bazadais cattle are called Purebred Bazadais, and are genetically different from Fullblood Bazadais. Fullblood Bazadais carry only and all of the genes that make Bazadais unique.