Colorful Coats Part 2

So now I'm going to discuss some more on the different alleles that can occur at Agouti. As I briefly mentioned in the previous blog post there are some 18 different options for alleles at the Agouti locus. A sheep can have any 2 of them including two copies of the same type of allele. However because of the way that sheep breeds were developed not all of these alleles are found in each breed. For example the Romney breed only has 6 alleles of the 18 that are common throughout the breed. Whereas the Romadale/CVM and the Navajo-Churro has around 9 alleles that are frequent through the breed.

Nightshade, our AaAa ram

As I mentioned in the last post the first of the these different alleles is the one that you see in most sheep. The White allele (Awt) is dominant to everything else and masks any of the other alleles so all you see is a white fleeced sheep. Now seeing that there are 17 other possible alleles, and explaining each of them would be too long for most people to read, I'm going to limit my explanation to the most common of these alleles. The next allele is known as the Badgerface (Ab). This gene exhibits as a half white and half black sheep. The white is along most of the dorsal part of the sheep. The exception is bars above the eye and from the chin working down into the brisket with the underbelly and inside legs exhibiting pigment. The next allele would be Black & Tan (At). This sheep is essentially the negative of the Badgerface pattern. With the belly and underside being white with white bars above the eyes while the rest of the sheep shows pigment.

The next three genes are darker genes with more than 50% of the wool on the sheep being pigmented. The first would be Light Blue (Albl). This is a sheep that has a black belly extending up to the rump as well as the nose and nose bridge with the rest of the animal having white fleece. In order for there to be a Light Blue there must be a Blue(Abl). The Blue allele shows black on all the inner and under areas with the shoulder tops, neck, and nose bridge with the rest of the animal appearing white. The last allele I am going to explain is the Self(Aa) allele. This results in an animal with absolutely no white pattern on it. It is a solid black animal that exhibits pigment in all of its skin and fiber. 

Frost, our AtAa ewe getting sheared.

Now these alleles work together or mask one another at times depending on the strength hierarchy of these alleles. As I mentioned earlier White is the most dominant and masks any other allele it is paired with. So some genotypes of a white sheep could be AwtAwt or even AwtAa but you would never know what that second allele is because the white allele masks it, unless you progeny test (topic for another day). For the rest of the alleles they work in a co-dominance fashion. So you could tell the difference between a AblAlbl and a AblAa due to the two alleles working together, just maybe not equally, but enough for the shepherd to determine the two alleles based on the color pattern. I may need to elaborate on this more later but I'll leave it here for now.