Horned/polled/scurred: an example of complete dominance, epistasis, and a sex-influenced trait.

A common DNA test on Simmental cattle is the Horned/Polled test. This genetic trait is an example of a completely dominant trait where an animal needs just one copy of the polled gene in order to show the polled phenotype. In other words, the polled allele will mask or hide the presence of a horned allele. A polled cow or bull can carry the horned gene without any outward display of the horned condition and pass the horned gene to their progeny. The polled gene and phenotype is also an example of epistasis where a second gene (scurred) affects the phenotype of the polled animal. Presence of scurs (typically small, movable, hollow pseudo horns) only occurs in heterozygous polled animals (carry one polled allele and one horned allele, Pp). Scurred is also a sex linked trait meaning the genetic inheritance is controlled differently in males than females. Scurs is a dominant trait in bulls meaning bulls only need one copy of the scurred allele to have scurs. Scurs is a recessive trait in females meaning a cow needs to have two copies of the scurred allele to display the phenotype (see below for possible genotypes and resulting phenotypes for the horned, polled, or scurred conditions).

Let’s use the following abbreviations for the horned, polled, scurred, and no scurs alleles:
P = polled allele and dominant
p = horned allele and recessive
S = no scurs (a different gene than horned/polled gene)
s = scurred (a different gene than horned/polled gene)

Horned/polled and scurred genotypes and the resulting phenotypes:
All homozygous polled (PP) animals are phenotypically polled independent of the scurred gene.
All homozygous horned (pp) animals have horns and are unaffected by the scurred gene.


Horned Polled Scurred Table

*All animals in this table are heterozygous for the horned/polled (Pp) gene. See above text for more explanation.

The heterozygous animals at the horned/polled gene (Pp) can either be polled or have scurs depending on their sex and the alleles for the scurred gene.


At present, there is no test for the scurred gene but you can test your cattle for the Horned/polled alleles through the ASA. To order tests send inquiries to DNA@simmgene.com.