Genetics of Pale or Dilute Coat Colors in Cattle
this page is part of a series "Genetics of Coat Color in Cattle"
This webpage was last updated on January 16, 2016 by Sheila Schmutz email@example.com
The bull at the left represents what is probably the most common white breed in Europe and North America, the Charolais. There are white cattle of many types and breeds however.
The gene or genes causing white have not all been discovered yet. White, as in the Charolais is actually caused by an epistatic or masking gene. This bull is actually red (e/e at MC1R), but it is not showing its red because it is homozygous for a mutation in the PMEL gene, common to Charolais. When this Charolais allele occurs in homozygous form, the animal is white. When it is only heterozygous, as in a Black Aberdeen Angus X Charolais calf the color is closer to grey or "smoke".
White in Shorthorn Cattle
White Shorthorn cattle, such as the cow pictured at the right, are white from a mutation in the KITLG gene or Roan series of alleles (see more below). The white in this case is only present in the homozygous condition, with the heterozygote being roan, and the other homozygote being red.
White with Colored Points
White cattle, such as White Galloway cattle are quite different from Charolais in that they have black noses and ears. This white is inherited as an autosomal dominant. Heterozygotes are not dilutions of another color but just as white as homozygotes. Their noses and ears can be either black or red or dun. Their underlying skin can be black or red or spotted. The White Galloway cow at the left is shown with a calf that did not inherit perfect white markings. White Park cattle, are similarly marked. Although an old breed, from the time of the Druids, they are now quite rare. Speckled Park cattle probably also fall into this category.
The colors of the points in White Galloway can be black or red, which is determined by the MC1R gene, described above, or dun, based on a mutation in the PMEL gene (Schmutz unpublished).
The white body color with colored points appeared to linked to the tyrosinase gene on cattle chromosome 29, based on data collected by Barbara Schmidtz for her Master's degree. Similar patterns exist in the mouse, Himalyan rabbit and the Siamese cat and also are caused by mutations at tyrosinase.
However, this pattern is caused by a very complex mutation in the KIT gene in cattle. A segment of DNA from near KIT on chromosome 6 is inserted onto chromosome 29. Although tyrosinase is near the centromeric end of chromosome 29, this insertion is apparently nearer the middle of chromosome 29. Brenig et al. (2013) further suggests that the whiteness depends on how many duplications of this segment occur.
Some people immediately think of albino when they hear white. However, most white cattle are not albino. However, the calf at the left is an albino and she has no pigment production at all, even in her eyes, which are pink. This is also called oculocutaneous albinism. This type of albinism occurs rarely, but can be present in various breeds and has even occurred in Bison.
This Braunvieh calf, Snowdrop, has a mutation in her tyrosinase gene (TYR) which renders it dysfunctional. This gene is the cause of several forms of albinsim in other animals and humans. She has a normal TYRP1 gene sequence, another gene causing albinism in humans. Both of her parents were of normal coat coloration and therefore we presume this albinism is a recessive, as are most forms of albinism in most species. A recessive form of albinisim was reported in Brown Swiss or Braunvieh cattle since 1934 at a very low frequency.
Note that another albino calf, a Holstein, did not have this mutation. Her albinism is either caused by another gene, such a P, or by a different mutation in tyrosinase.
Dilute has come to have a negative connotation to some ranchers. I often use the word pale to try to break that connection.
The PMEL gene is now known to be the gene responsible for dilute vs dark colors. At the top of the page, Charolais cattle were mentioned. They are homozygous for one mutation in this gene.
Other breeds, such as Highland and Galloway, have another mutation in PMEL. Dun is the name given to a pale color in cattle such as Galloway or Highland. In Galloway and Highland cattle, Dun is dominant to black. Silver dun is the color resulting when Galloway cattle are homozygous for this allele. The gene causing this coloration is PMEL. The Galloway heifer, at the right, is also called dun which is a dilution of black in these breeds.
In Highland cattle, the dark red (D/D), illustrated by Dominique at the left below, is harder to distinguish from the pale red (D/d), illustrated by Dahlia on the right, than black (D/D) and dun (D/d). For this reason, some owners may want to DNA test their cattle to determine which carry the d allele. The d/d animal would be cream to white. All colors of Highlands have always been accepted, since the beginning of their herdbook.
The three bulls shown above are purebred Simmentals that illustrate the variation in "red". The palest bull on the right would be considered a dilute by most cattle owners. The identity of the mutation or mutations causing paler colors in Simmental has not been clearly identified.
In 2003, MATP or "underwhite", now known as SLC45a2 was found to be the gene causing palamino in buckskin in horses. One copy dilutes a sorrel to palamino and two copies to cremello. All these horses are producing only phaeomelanin. On the other hand a bay is producing eumelanin also which is evident in its mane and tail. One copy of this SLC45a2 mutation in a horse that also produces eumelanin results in a buckskin and two in a perlino. We have done a small experiment using markers near this gene in cattle and did not find that this gene fit as a diluter gene in cattle.
Gray in Belgian Blue
Late in 2015, the genetics group in Belgium discovered that a few Belgian Blue cattle that were gray instead of black were homozygous for a mutation in exon 2 of the MLPH gene. They also reported that this mutation was not found in any other breeds they examined.
We studied this area of the gene in Braunvieh and the mutation was not present in them either.
In Dexter cattle, there are black and red ones and then others that are called dun. The dun colors really seem to range from brown to yellow and are inherited as a recessive trait. The photos below and data for the above statements were provided by John Potter. This color is due to a different gene than the color called dun in Galloway cattle or Highland cattle. We have recently developed a carrier test for this mutation in the TYRP1 gene.
for further information contact:
Sheila M. Schmutz, Ph.D., Professor Emerita
Department of Animal and Poultry Science
College of Agriculture
University of Saskatchewan
Saskatoon, Canada S7N 5A8
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