Color Genetics, Color Patterns and
the Pygmy Goat
By D. Phillip Sponenberg, D.V.M., Ph.D.
Reprinted with the author's permission
All rights reserved
Color variation is part of the fascination of raising Pygmy goats. These colors all result from gene interactions, and a look at the genes present in the breed can reveal the colors and patterns that are possible in Pygmy goats.
A few concepts of color are important to grasp before any discussion of color genetics can be meaningful. Some of these concern the mechanisms by which color is produced. Color is due to melanin deposits in the hair. Each goat has a genetic directive for the placement of certain colors of melanin in the hair. White areas on goats, or entirely white goats, result from this directive being superseded by genetic directives that prevent melanin from being placed in the hair. This occurs through a wide range of mechanisms; the details are less important than the general fact. The importance of this is that white areas need to be viewed as covering up colored areas, much like white paint. The tendency of most people is to see color as added to a white background, when in reality the opposite is the case.
Melanin is deposited in the pigment granules responsible
for color; these come in two basic types - eumelanin and pheomelanin. Eumelanin
is usually black, but sometimes brown, and it is the pigment responsible
for black and brown areas on goats, or rarely for dusky blue color. Usually
the color choices with this pigment are either/or; the goat can either form
black or brown, but not both. Pheomelanin pigment is responsible for red,
tan, or yellow pigment. That sounds easy enough, but if pheomelanin is very
dark it can be close in shade to the brown eumelanin pigment. Pheomelanin
usually has a redder cast to it, though, and the difference between the two
types is generally fairly obvious. "Red" pigment can also be pale enough
to be cream or nearly white, and this can cause confusion in some
Dominant and Recessive Genes
Finally, we get to some real genetics. Genetics can be confusing and is not always intuitive. It is important to remember that genes occur in pairs. Each parent transmits only one of its pair to its offspring. This sounds easy , but it is critical to remember that each goat only has two genes at each locus, or "address." So, while a goat has four grandparents, it can only have two genes at a color locus from these four, which means that someone got left out. We know that the sire and dam each must contribute one, but grandparents get much iffier.
An example may help. If a buck has a caramel father and an agouti mother, he may well be agouti, not caramel. If a doe has a caramel father and a black mother, she may be black. If we cross the black doe to the agouti buck, it is impossible to get a caramel kid, even though two grandparents are caramel. What happened in this case is that the caramel gene simply did not make it through to the parental generation, so it is not present to be donated to the grandkids.
Genes are also said to be dominant or recessive. This
only describes their interactions with one another in pairs and says nothing
about their prevalence in a population. A dominant gene can be rare, and
a recessive gene can be common. The trick here is that a dominant, when paired
with a recessive, masks the recessive. So, an animal with a dominant trait
can have two doses of the dominant gene, or one dose of the dominant and
one dose of the recessive, and the differences cannot be told by only looking.
A goat with a recessive trait, in contrast, must have two doses of the recessive
gene. The real importance of this is that recessive traits can pop up out
of nowhere, since they can be masked by dominant genes. A dominant trait
cannot pop up out of nowhere, since it cannot be masked. A good example of
this is in Angus cattle. Every now and again, red calves occur in black herds,
as red is recessive to black. The opposite situation - black calves in red
herds - never occurs, for the red recessive cannot hide black.
Three basic colors occur in Pygmy goats, and two patterns
can be superimposed over them. The basic colors are black, dark brown/mahogany,
and medium brown. As solid colors, these are fairly rare in the breed, but
they are the underlying base for the common caramel and agouti patterns.
In the Pygmy, black is dominant to the recessive medium brown, so medium
brown can pop out as a surprise. Dark brown is dominant to black, and this
seems to be the more common type of brown in the Pygmy. This means is that
it usually takes a dark brown (or dark brown + pattern) goat to produce a
dark brown (or dark brown + pattern) kid. The recessive medium brown is an
exception to this rule, and will occasionally pop out as a surprise from
black to black matings.
Medium brown is more rare than dark brown, and it is recessive to black. Medium brown goats, therefore, must have two medium brown genes. If medium brown goats are mated to black goats, the results depend on the black parent. If the black has two black genes, all the kids will have one black and one medium brown gene, and they will be black. If medium brown goats are mated to black goats with a medium brown parent, it is certain that they have one dose of the medium brown gene and can contribute that to half of their kids. As a result, they can be mated to medium brown goats to produce 50% medium brown and 50% black kids. The fun begins from an understanding that the recessive colors can lurk undetected for generations. So, if a black goat has an unseen medium brown gene and is only mated to black goats without a medium brown gene, the result will always be black kids. If one mate carries the medium brown, though, a medium brown kid can occur as a surprise.
So far, the basic lesson is that you have to breed to
a dark brown to get one. Medium brown can occur as a surprise, but the only
consistent way to produce them is to mate medium brown to medium brown, or
medium brown to a black goat with a medium brown parent.
|Basic colors are usually "dressed up" in the Pygmy, and so are fairly rare in their basic form. One pattern that can be superimposed over the basic color is the agouti pattern. This is the familiar mixture of white hairs into the base coat color. Since this is superimposed over the basic color, the result is six choices for color: black, dark brown, medium brown, black agouti, dark brown agouti, and medium brown agouti. The agouti pattern varies in intensity, so that shades within the pattern are variable with some lighter and others darker. The agouti pattern is dominant to its absence, so agoutis are expected to sometimes produce solids, but two solids mated together should never produce an agouti. In the few instances in which this happens a further investigation usually reveals that one parent is a very dark agouti.
|The basic pattern with the agouti is that some agoutis have two doses of the agouti gene. These mated to solid colored goats (usually black, but maybe dark or medium brown) result in all agoutis (on a black background, dark brown background, or medium brown background as determined by the previous examples). If an agouti has one agouti gene and one solid gene (as the kids from the previous matings would have to have, since they have a solid parent), the result of matings to solid colored goats would be 50% agoutis and 50% solids. Solid-to-solid matings cannot produce agoutis, since the gene is dominant and expresses itself even if present as a single copy of the gene.
Caramel is the second major pattern. In genetic parlance this is called badgerface after a similar sheep color pattern, but the name caramel is used in pygmies, so let's stick with it. The caramel pattern consists of a tan or cream body with dark belly, dark legs, dark marks on the face and a dark stripe down the back. The caramel pattern can be superimposed over the basic colors, and the result is caramels with black marks, dark brown marks, or medium brown marks. Since the main feature of caramels is body color, they are frequently referred to by body color rather than the color of the belly, legs, face markings, and back stripe. These dark areas reveal the underlying color of the goat, though, and their color is therefore important. Caramel is dominant to the solid colors and is really superimposed over them. As a result, two caramels mated together can sometimes produce agoutis and solids. Two solids mated together cannot produce caramels. Neither can two agoutis mated together, or an agouti and a solid mated together. So, the basic rule is that you need to mate to a caramel to produce one. This is the key concept of a dominant gene.
Table 1 should help in understanding that dominant genes
cover up recessive genes. If this theory is true, then individual caramel
goats mated to solid goats should produce kid crops of three different sorts:
* All caramel
* 50% caramel and 50% agouti, no solid
* 50% caramel and 50% solid, no agouti
Caramel goats can have one or two doses of the caramel gene. As a result, they can produce various offspring. One theory is that each goat can only have two choices of caramel, agouti, or solid. This means that the colors in Table 1 could have these genetic makeups:
The key point is that no one goat should provide all three choices to a kid crop. The question is, has anyone had a caramel goat that when mated to solid mates produced all three patterns? I have not come across one, but such a goat would be important in proving or disproving the above theory.
|50% caramel, 50% agouti
|50% caramel, 50% agouti
|50% caramel, 50% agouti
|50% caramel, 25% agouti, 25% solid
The depth of the caramel color is variable, from nearly
white to nearly brown, with tans and reds in between. The shade of color
is controlled in a more complicated fashion than the basic pattern, and there
are many questions about this. Most of these differences seem to be due to
multiple genes, and the best recommendation is simply to mate the preferred
shade back to itself (red x red, tan x tan). Then keep your fingers crossed.
I have had lousy luck in my own herd in predicting shade. I have a passion
for rich gold and always seem to get white, cream, or dark red, even out
of a magnificent gold buck.
Some Pygmy goats are white spotted. These patterns have
never been adequately studied. The belting pattern, which is variable in
expression, is dominant. Its expression is so variable that it is a difficult
pattern to predict with any certainty. I suspect that there are other spotting
patterns besides belting and that these are independent genetically, but
none of these has been documented as to genetic mode of inheritance.
The typical frosting on the Pygmy ears and muzzles is due to a dominant gene. This is so common in the breed that I have never seen a Pygmy without frosting. The amount varies, but at least some is usually there.
All the Possibilities
With all of these components it is possible to make a variety of color.
Dark Brown Agouti
Medium Brown Agouti
Black Trim Caramel
Dark Brown Trim Caramel
Medium Brown Trim Caramel
It can be seen from the table that there are basically nine colors within the Pygmy goat breed. All of these can occur because the genetic machinery exists within the breed to form these colors, with or without added white spotting. Except for the solid dark brown and solid medium brown, all are accepted within the NPGA Breed Standard. Even though solid browns are not, they are very much possible because the genetic machinery is there.
These nine combinations are complicated by the addition of white spotting in some goats, which results in eighteen basic types, one spotted and one nonspotted. The important basic concept is that each goat is the combination of different factors. These are under separate control, so the choices can be viewed as a cafeteria with various choices for courses. The choices are:
|1 - Black
2 - Dark Brown
3 - Medium brown
|1 - Nonagouti
2 - Agouti
|1 - Noncaramel
2 - Caramel
|1 - Nonspotted
2 - Spotted
|1 - Frosted
2 - Nonfrosted *
|We can only pick one color trait from each group. As an example, a caramel goat with medium brown trim and a spot on the side is A3, B2, C2, D2, E1. Similar logic can show the choices for all the other colors. * I have never seen this in pygmies, so it may not be a choice.
A few other patterns probably pop up occasionally in the Pygmy. This is expected because caramels can mask a number of other patterns. These are probably culled because they are not recognized in the standard. They are just as much a part of the breed as similar recessive colors are in other breeds of livestock. I have seen one "reverse caramel" Pygmy, with a black body and light belly and legs. The pattern would be easily masked and pop out unexpectedly on occasion. This pattern and others reflect the Pygmy's African origin, where color is unimportant and survival and production are.
It is interesting to see how the color factors that are present in the Pygmy breed can interact to give various final colors. Colors add even more interest to an already interesting breed, and all of them should be appreciated by devoted followers of the breed.
|Dr. Sponenberg is a Professor of genetics and pathobiology at Virginia Polytechnic Institute and State University and has worked to conserve rare American breeds for thirty years. Internationally known for his work in color genetics, he has authored numerous books and publications. His experience includes that of both an academic and an animal breeder, allowing him to utilize practical as well as theoretical aspects of breed conservation.