go home little cow
an informal discussion of
Dun and Red Genetics in Galloway Cattle

Alan S. Bias, administrator, Galloway Cattle Genetics Discussion Group

Miniature-Cattle.com genetics DNA tests for different breeds of cattle Dun & Red genetics in Galloway cattle
related article: Choosing a breed of Miniature Cattle (and what to know about registries)
related article: Breeds of Miniature Cattle
related article: More Breeds of Cattle for the Small Homestead

Unfortunately, most registries were started by “laymen” who assign "color classes" by phenotypical observation and not genotype. Not to single out, but let’s just use the American Galloway Breeders Association (AGBA) as an example. The AGBA registers three solid colors; Black, Red and Dun. There are two immediate issues that arise from this classification of “color”. First, not all “Red” are red, i.e. Wild-Type Red is not Red by genotype. Rather, only by phenotypical observation (what the eye perceives). Second, “Dun” is a dilution of color, and not a color in itself. Though, to be fair, if the AGBA views “Dun” as a color, it is consistent in registering both Dun Black and Dun Red under “Dun”. The reasons will become clearer as you read on…

DEFINING COLOR: Solid coat color in cattle results from the presence or absence of melanin (eumelanin “black” and phaeomelanin “red”) in hair coat. These melanocytes migrate from the neural crest during embryonic development. As hair grows, melanocytes are transferred to the follicles to produce pigment. Further traits can modify color coat in utero, shortly after birth or with aging. Additional traits in turn can modify for spotting or pattern.

The Melanocyte Stimulating Hormone Receptor Gene (MSHr), also called the Melanocortin Receptor 1 gene (MC1r) is the source of all black or red hided Galloways. This gene has two common alleles, dominant (ED), and recessive (e). In addition, a less common allele (E+) also called "wild-type" occurs. An animal with (ED) present is always black. This allele is dominant to (E+) and (e). Cattle that are (e/e) are the recessive genotype red.

EXTENSION: Solid Black, Red and Wild-type Cattle are the result of Extension (E) locus: ED = black, E+ = wild-type (black/red) and e = red. Extension regulates the levels of tyrosinase. High concentrations of this enzyme result in production of eumelanin (black pigment), while low concentrations of this enzyme result in the production of phaeomelanin (red pigment). The accepted order of dominance is ED > E+ > e. It is possible Galloways have additional types of Extension other than (E).

BLACK: The black allele is abbreviated (ED). The E stands for Extension, and the subscript D stands for dominant black.

RED: The red allele is abbreviated (e). Lower case is used to indicate that the allele is recessive to the other two alleles for color (ED) & (E+).

WILDTYPE: The wild-type allele is abbreviated (E+). The superscript + symbol is used to designate a wildtype allele. Initial color coat testing done on Wild-Type Reds during the 1990s by GenMARK concluded at the time these animals were heterozygous black (Bb). Wild-Type Red animals have deep burgundy red bodies. The extremities (head, neck, feet) appear to be black from a distance. When viewed up close or in natural sunlight the red coloration is visible down to the root. While in Galloways, Wild-Type Red appears to result from Extension (E+), reports of Agouti (A+) influence has been suggested in other breeds.

Wildtype alleles produce both eumelanin and phaeomelanin through intermediate amounts of tyrosinase. The ratio and distribution of these two pigments may be modified by other genes. The visible expression of eumelanin seems sex linked. This can be observed in wild-type (E+) bulls, which express a darker head, neck and feet as compared to females. Current studies indicate the (E+) allele is responsive to agouti in patterned & brindle animals.

Individuals with wildtype coloration can be homozygous for the wildtype allele (E+/E+) or they can be heterozygous for the wildtype allele with one dominant black (E+/ED) or one recessive red allele (E+/e). Inheriting one allele from each parent.

Heterozygous (E+/ED) are most often dark black in color, since even one copy of ED will produce an over-abundance of eumelanin. In heterozygous (E+/ee) variability of coloring in these animals is expected, and poorly documented. Either combination of alleles (ED/E+) or (ED/e) will pass the wildtype allele (E+) to offspring 50% of the time.

AGOUTI: E+ can be further modified by the Agouti (A) locus. Agouti comes in several forms and has distinct effects depending upon combination. It is not well understood or documented across breeds. The existence of a recessive black Agouti allele (a) has been postulated with some supportive documentation, having the effect of modifying Wild-type E+ black/red to black. Thus, not all phenotypical “black” animals may be black (ED/ED). Again, as with Extension, it is possible Galloway’s have more than one type of Agouti in genotype. To touch on briefly, the suggested allele (Abp) is epistatic (dominant) to ED and hypostatic (subordinate) to E+. In combination with ED, Agouti is not likely visible. In combination with E+ results in very dark Wild-type; expressing not only varying degrees of red, but also locations of red on the body. The allele (aw) is recessive and will remove red pigment; leading to the illusion of evenly distributed black melanocytes on the body of Wild-type E+, mimicking a black animal.

DUN: Dun Galloways express in three primary phenotypes: Chocolate, Golden and Silver. Golden dun results from heterozygous codon deletion within the PMEL gene (p.Leu18del) PMEL +/del. Silver dun results from homozygous codon deletion within the PMEL gene (p.Leu18del) PMEL del/del. From a breeder aspect this simply means the dun trait within various Galloway populations is an autosomal incompletely dominant trait; .i.e. it only takes a single dose for partial expression in heterozygous form.

While Dun may present in spotted (White Park) and patterned (Riggit & Brindle) Galloway’s, the locus is only a mutation of solid color, i.e. black or red. The presence of spotting or pattern traits has no effect on the expression of Dun. Thus, there are two common “Dun” phenotypes: Dun Black and Dun Red. Dun modifies black or red, and should be stated first in name or genomic descriptor.

With autosomal mutations of color across species, such as Agouti and Dun, both recessive and incompletely dominant, variation of color (shading) is to be expected. This as a result of “autosomal concentration”, .i.e. a sort of cumulative effect. Just as an autosomal incompletely dominant trait has distinct impact in both heterozygous and homozygous fashion, so does an autosomal recessive trait. Only in the latter it takes much observation to take note of the subtle differences presented in the heterozygous form of a recessive. Thus, all light-colored animals are not the result of Dilution genes.

Dun is dominant to black. The effect on red is more uniform. Homozygous red (e/e) animals that are also heterozygous at the Dun locus will be duns. Animals that are homozygous Dun show a more extensive reduction in pigmentation in both black (ED/ED) and red (e/e) coloration. A homozygous black Galloway (ED/ED), but also homozygous for Dun, will appear silver. On the other hand, individuals homozygous for Dun and also homozygous red (e/e) would look very light red or even yellow. Animals heterozygous or homozygous for Dun and (E+/E+) or (E+/e) will be darker than (e/e). The actual shading will vary depending upon specific combinations (zygosity).

CHOCOLATE DUN: Is likely the result of combination of Dun with various types of E and A alleles in co-expression.

 

Which brings us back to the subject of a prior discussion, (about red, orange & yellow looking cows and semi-dominance of the dun dilution) ...the Cross Creeks cow and calf (left). The cow and calf appear to express identical genotype. JP Zuccaro, your current sire is APS Dax 17D, genotype non-dun (E+/e). Quick look on CLRC suggests there is no indication of Wild-Type Red in the pedigree of dam TUM 25D: RSS URI Sund RSS URI SUNDOG 10U (DUN) -[CAN]22636- x GOWRIE STRAWBERRY WINE (RED) -[CAN]22343-. Even though both dam and calf are bit dark in the nose, we'll assume Dax only passed (e) to calf, and not (E+). I would assume genotype of both dam and calf to be (del/del,e/e) or (+/del,e/e). Think the latter as noses are dark. Thus a heterozygous Dun Red with a single dose of Dun.

 

This informal article is generously provided by Alan S. Bias, and is the result of discussions in 2018
on the Galloway Cattle Genetic Discussion Group. https://www.facebook.com/groups/610010689066993

see also:
Dun Galloway Genetics ; a discussion of effect on phenotypical expression. Paper by Alan S. Bias, March 16, 2015


About the Author: Alan S Bias is an independent researcher active in evolutionary biology as a member of Independent Academia, and has published many papers that document his research findings. In this article, he shares some of his knowlege about the genetics of the most common dilution in beef cattle. Alan is a rare Shetland Sheep, Galloway Cattle and Domestic Guppy breeder & exhibitor of 47 years. For the last 35 years he has specialized in strains known to breeders as "Swordtail Guppies". For nearly 20 years he has done cellular level research, combining formulated breeding tests & systematic observation to help breeders understand the complexities of modern Guppy genetics in the strain being produced. Alan lives in Lewisburg, West Virginia, United States. alansbias@aol.com

go home little cow
go home little cow

publisher: Vintage Publishers
published online: December 2018
author: Alan S. Bias