Polled gene
The inherited variant on cattle chromosome 1 that stops horns from forming.
Also: polled locus, POLLED, P allele
Hornlessness in cattle is controlled by a stretch of chromosome 1 called the polled locus. At least two different variants there cause it: the Celtic variant, found in breeds of British and northern European origin such as the Angus and Galloway, and the Friesian variant, found in polled Holsteins. Both are dominant, so a calf needs only one copy from either parent to be polled. A bull with two copies, called homozygous polled, sires only polled calves, which is why breeders test for it. Polled bulls of high merit are now in demand in dairy breeding, where dehorning calves is otherwise routine. Scurs and some other horn types follow separate genes.