What Colors Are Yaks?
Color Inheritance in North American Yaks: Black, Black, and Gold
Three colors are recognized in North American yaks: Imperial Black, Native Black, and Golden.
Black Imperials: Frequently coal black at birth, Imperials are black with a shiny black nose. As they develop, depending on how wooly the animal is, they often take on a reddish cast from sun exposure. The silkier the coat the less likely it will be changed by exposure to sunlight. The reddish cast may be due to modifying or casting genes that act in the presence of the primary black gene and interaction with sunlight to create the reddish cast. This can also be seen in Black Angus cattle, Friesian horses and many other livestock breeds.
Native Black: Native Blacks are black hided animals with a grey or brown muzzle. Some individuals will show a grey or grizzly dorsal stripe, which is considered by some a more ancient wild-type trait (Weiner, G., 2014). Native Blacks vary from a near dark black to brownish.
Golden: Goldens have, you guess it, a golden honey brown color, but can var from light red to a more brownish red. These beautiful creatures are rare and the gene that creates this color is recessive, which some believe they are the remnant of nomadic cross-breeding with cattle. More genetics research by IYAK is needed to see if this is the case in our registry.
“The Golden yak color is inherited as a recessive trait that requires the homozygous genotype for phenotypic expression. The heterozygous genotype is not expressed, but is a recessive carrier. The inheritance is identical to the red gene in Red and Black Angus cattle.” - IYAK Genome Committee, 2014
The Research is In: White yaks aren’t really yak.
White yaks are more common in Asia, but whether in North America or on the Tibetan Plateau, researchers agree there is only one way to get a white yak - hybridize. Hybridization is the controversial practice of mating two different species that do not normally mate to derive new genetic characteristics. A research study in 2015 shows that the Tianzhu white yak in Asia is less genetically similar to yak (Bos mutus gruinnins) than are the American Bison (Bai, J, et al., 2015). Which is odd because while bison is our closest relative, it is a different species (Bison bison). Another study in 2012 demonstrated that there were known cattle mutations that occur to create the white coat color (Qui, Q, et al. 2012). This is important because it is the result of 2 species crossing (Bos mutus gruinnins x Bos taurus or Bos indicus) - creating a hybrid species. Not exactly a yak.
These hybrids are are helpful to ranchers breeding yak for meat production, but these terminal animals should not be bred themselves. You may have head the term Genetic Pollution bandied about in the media and by Conservation Biologists at the United Nations. Genetic Pollution is used to describe gene flows between modified or domesticated species and their wild relatives. The opposite of Genetic Pollution are True Genetic Breeds. These True Genetic Breeds are important to folks protecting Heritage Breeds, like the Livestock Conservancy, because well, extinction.
Color Patterns: Solid, Stared and Spotted (or Solid, Trim and Royal)
There are three yak color patterns in North America; Solid, Trim and Royal.
Solids: Solids are completely black or brown with no white patterns.
Trims: Trims typically display a white star or stripe on their forehead. Rear legs, and sometimes all four legs, have white socks and 1/3 to 1/2 of the tail will be white. We have seen full white tails in Trims which is considered a wild-type ancestral remnant (Wiener, G. 2014). The amount of white does not determine if the animal is a Trim; even a small expression of white qualifies the animal as a Trim. There are three Trim colors: Native Black Trim, Imperial Trim and Golden Trim.
Royals: Royals exhibit a piebald pattern with a pink muzzle and tongue. They are black and white or gold and white. They usually have a full white tail and piebald pattern throughout the torso with white usually continuous under the belly. The face usually has a broad white stripe. The amount of body white varies significantly from about 10% to less than 90%. On occasion we will see some very small spots, but never a true roan. Some people have referred to this pattern as a Holstein type pattern - descriptively vivid but erroneous. These beautiful creatures are rare and some believe they are the remnant of nomadic cross-breeding with cattle. More genetics research by IYAK is needed to see if this is the case in our registry.
Breeding for Pattern and Color Inheritance
Pattern inheritance is very simple. Royals are homozygous for the Royal color pattern. Trims are heterozygous for their color pattern and Solids are homozygous for the solid pattern. The mode of Royal inheritance is incomplete dominance where the heterozygous genotype results in a partial expression that we designate as the Trim phenotype. I will designate the Royal genotype as RR, the Trim genotype as Rs and the Solid genotype as ss.
Imperials are either homozygous Imperial or heterozygous Imperial. Only one copy of the Imperial gene is required for the Imperial gene to dominate over the Native Black or Gold colors and produce Imperials. A homozygous Imperial bull will always produce Imperial offspring when bred to Native Black females. When bred to Royal females he will always produce Imperial Trims. A heterozygous Imperial bull will produce a mixture of Imperial and Native Black offspring when bred in the same manner.
How Genetic Testing Can Help
When you register your animal with IYAK we provide proprietary genetic testing and analysis that gives you information about the specific genes that your animal carries that influence coat color. This can help you reach your breeding goals by letting you know which animals are more likely to give you the desired outcome and which you should cull. For more information see Reading Your Genetic Registration Report (here) and IYAK Genetically Outperforming Tibetan Yak (here).
Nicole Porter-Salvato, PhD is one of the caretakers and founders of Prairie Sky Sanctuary, a horse and yak ranch in SW Wisconsin. She’s trained in epigenetic and epidemiology, an avid IYAK supporter, BOD member and yak lover. She and her husband, Dan, love to talk about yak and are always available to answer questions or provide resources.