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Simmental, Hereford, and Gelbvieh cattle can carry a mutation in a gene (called Pmel17) which causes a black coat color to be diluted to a grey color. This is a different mutation for coat color dilution from Charolais cattle. The dilution mutation is masked in red cattle (or at least not as obvious as the dilution effect in black cattle). The control of red or black coat color is on a separate gene from the dilution mutation, but the dilution mutation can affect the expression of the coat color phenotype. This is a phenomenon called epistasis when the expression of one gene is affected by a second gene.

As discussed in a previous forum, all red animals are recessive for the coat color gene. Let’s call the red allele “e”. Black haired animals can either carry one (heterozygous, Ee) or two black alleles (homozygous, EE). Like the black coat color phenotype, dilution is a dominant trait so it only takes one mutated gene to see the dilution. Let’s call the dilution mutation “D” and the normal Pmel17 allele “d”. Therefore, if an animal carries one copy of the dilution mutation and one normal allele for the Pmel17 gene, you would expect that half of their progeny will inherit the dilution mutation and the other half the normal allele. Whether or not the progeny appear to have a diluted coat color is dependent on the coat color of the offspring. All the black calves with the dilution mutation will have a grey coat color. The black calves with the normal Pmel17 gene will be black. All the red calves will most likely appear normal (although those with the dilutor gene may have a slightly lighter red color). The following list represents the genotype (what alleles the animal has; E = black coat, e = red coat, D = dilution mutation, d = no dilution) and the resulting phenotype (coat color appearance):
E_/dd = Black
E_/D_ = Grey
ee/dd = Red
ee/D_ = Red (might be slightly lighter in color)

Why is it relevant to understand the above information? If you have animals that are black, you probably don’t need to test them for the dilutor gene as they would appear grey if they carried it. However, your red animals can “hide” the dilution mutation without notice. Therefore, if you are mating red animals to black animals and you don’t want any grey calves, you should test your red animals for the dilutor gene.

To order the dilutor test, please contact the ASA at This email address is being protected from spambots. You need JavaScript enabled to view it.