As I've discussed, all sheep are genetically either black or brown - at the B locus. The expression of that color can be modified by genes at the pattern locus, which is called A, and regulated by a gene at the Extension locus, E. Sheep can have color from the two different pigments (eumelanin and phaeomelanin) in a number of different "patterns". Basically, anytime you see a regular distribution of light and dark color in a sheep, it probably is due to the A locus. Unlike B - where there are only two possibilities, at A, there are at least 6 possibilities and many people believe there are a lot of patterns and variations that are as yet unidentified. It is the most complex of the sheep color genes.
The first pattern allele is the most simple and also the dominant one - and that is White. White is a "pattern" known as AWt for white/tan because the tan pigment (phaeomelanin) is interchangeable and often intermixed with white on sheep. In the sheep world, white is the most common color - now you know it is the most common "pattern". Even though a sheep might be black (eumelanin) at the B locus, if it carries even one copy of the AWt allele at the A locus, it will be white! The AWt allele has the effect of inhibiting one of the metabolic steps in eumelanin synthesis, so although the sheep has the gene to make the black pigment, the AWt gene stops it from doing so.
We know the Gotland sheep pattern is NOT AWt. (hint - Gotlands are grey, not white)
The second pattern is the recessive one - Solid color. A whole, solid color is recessive to all of the other sheep patterns. The lambs on the previous page are Solid patterned. It is known as Aa, and since it is the most recessive pattern, any solid sheep must be homozygous Aa/Aa. (We haven't gotten to the Gotland pattern yet....)
With just these two alleles at A, you can predict several genotypes. A solid, brown sheep as shown in the photo in the previous section must be Aa/Aa Bb/Bb, the most recessive genotype. A solid, black sheep has two options Aa/Aa BB/BB or Aa/Aa BB/Bb. A white sheep only has to have one copy of the AWt allele, and that white hides other patterns and the basic color. Now you know how colors and patterns can hide in flocks of white sheep for many generations until the right (or wrong!!!) combination of sire and dam brings out the phenotype. Here are some possible genotypes for a white sheep:
AWt/Aa BB/BB - white sheep, produces white and/or black lambs (if paired correctly)
AWt/AWt BB/BB - white sheep, will only produce white lambs
AWt/Aa BB/Bb - white sheep, produces white, black and/or brown lambs (if paired correctly)
AWt/Aa Bb/Bb - white sheep, produces white and/or brown lambs (if paired correctly)
Below is a Punnett square showing how two white sheep can produce white, black and brown offspring:
Sire (AWt/Aa BB/Bb), Dam (AWt/Aa Bb/Bb)
|Sire (below) Dam (right)||AWt, Bb||AWt, Bb||Aa, Bb||Aa, Bb|
|AWt, BB||AWt/AWt BB/Bb||AWt/AWt BB/Bb||AWt/Aa BB/Bb||AWt/Aa BB/Bb|
|AWt, Bb||AWt/AWt Bb/Bb||AWt/AWt Bb/Bb||AWt/Aa Bb/Bb||AWt/Aa Bb/Bb|
|Aa, BB||Aa/AWt BB/Bb||Aa/AWt BB/Bb||Aa/Aa BB/Bb||Aa/Aa BB/Bb|
|Aa, Bb||Aa/AWt Bb/Bb||Aa/AWt Bb/Bb||Aa/Aa Bb/Bb||Aa/Aa Bb/Bb|
One eighth (2 squares of 16) of the theoretical offspring are brown, one eighth are black. The other 75% are white, some of which are homozygous white (25%), the others are heterozygous white (50%). They all vary in whether they are brown or black, or black carrying brown. This is a lot of variation with just two gene loci! This square hints at just how complex, yet predictable, color genetics can be.
Now, the patterns get interesting - and more complex. The other pattern alleles at A control the distribution of white, black, brown and tan fibers. They are recessive to white, and dominant to solid. They can coexist with each other... very interesting!
The sheep below is a purebred Shetland ewe. Her basic color is BROWN. (Note there is no black on her - not her nose or hooves or lips or eyes.) She has a pattern of light and dark, brown and tan, especially on her face and legs. This pattern is known as "badger-face" or in Shetland-ese "katmoget", and is noted as Ab.
Badger-faced sheep have this pattern of light and dark on their faces and legs, plus they have dark bellies usually with a dark stripe running down their throat and up to their tail. Their upper bodies are light colored, either fawn (in brown based sheep) or grey (in black based sheep). The tan areas (forehead, cheeks, knees, inside legs) can be very rich or almost washed out white. The Grey Katmoget Shetland ewe below has very rich color, shown best right after shearing and before any sunbleaching takes place.
Next pattern! This one is often called "reverse badgerface" since the sheep are dark on top and light underneath. It is also known as "Mouflon" or "Gulmoget" in Shetland-ese, and sometimes "black and tan", and is noted as At. Mouflon sheep have a distinctive facial pattern. Note the light teardrop/eye splashes and underjaw on the Shetland ram lamb below. The light neck, chest and underbody, and tan lower legs are also typical of this pattern. What basic color is this ram? Brown? Right! Mouflon sheep can also be black based. Can they be white with this pattern? Nooooo, white is dominant, so if a sheep has a gene for white they are solid white. If a sheep is white AND mouflon (AWtAt) they look solid white. (This photo was taken just after this ram broke a horn - poor little guy!)
Here's another question - can a sheep be Badger faced and Mouflon??? Well, yes. The two patterns can co-exist. It is called co-dominance. The genetic notation is AbAt. The ram below is At/Ab (or Ab/At - they mean the same thing). He looks like he has a regular pattern, but it's not quite Badgerface, and not quite Mouflon, kind of "muddy" and indistinct. All of his offspring are either badgerface or mouflon. Pretty neat, right? Well, not if you're breeding Gotlands!
This next pattern is commonly found in the luster longwool breeds. It can be fairly subtle or very distinct. The "English Blue" pattern (Abl) is evidenced by a characteristic light teardrop on their faces as the Wensleydale/Gotland lamb below shows. They can also have the light muzzle and grey fleece in lighter or darker shades as they mature.
The 50% Gotland lamb below also shows the characteristic English Blue markings. It already shows shading characteristic of both the Abl pattern (light sides and tail) and of the Agg pattern (light neck ring and suger lips). Some English Blue sheep are very light in color as adults. Their faces are still dark with the characteristic teardrops. These two examples are BLACK based. Though not as common, English blue sheep can also be BROWN based.
As with the co-dominance of Mouflon and Badgerface, English Blue can co-exist with Mouflon or Badgerface. Can all three coexist? Noooooo, each sheep only gets TWO genes for pattern from its parents - one from Mom and one from Dad. So, Ab/At, Ab/Abl, At/Abl are all possible combinations. I'll bet it is difficult to tell by looking at a sheep if it is At/Abl! The At would probably overlay/wash out the Abl enough that Abl would not be distinct enough to identify. By the way, a sheep can also be homozygous (two copies of the same gene) for each of these patterns - At/At, Ab/Ab or Abl/Abl. The offspring of each of these homozygous sheep will be the same pattern as they are (unless they get a white pattern gene that covers up everything!)
The LAST pattern gene I'm going to address is (finally!) the one of interest to Gotland breeders. This one is called "grey" - what else??? It is known as Ag. There are some who believe Gotlands might have their very own pattern, designated Agg. So far, at least, the existance of Agg has not been proven. I am going to use it. If you don't believe in Agg, just think "Ag" wherever I write Agg. Ag (or Agg) is dominant to the solid pattern and recessive to the white pattern. It is co-dominant with Ab, At, and Abl.
Ag (or Agg) has the effect of interspercing white fibers in the fleece as the animal matures. Typically, the lambs are born solid black (or brown) with characteristic white "sugar lips", and wisps of white inside their ears and groin. The half Gotland-half Finn lamb below has classic "sugar lips". She was even into the sugar with her nose! Ag and Agg lambs start turning grey dramatically within a few weeks of birth. It is as if a switch were flipped - and the new fleece comes in grey all at once. If they are still solid black (or brown) by the time they're 8 to 12 weeks old, they're probably NOT Ag or Agg.
Sometimes Ag grey lambs can be quite wild in their mix of color, especially in Shetlands. This Shetland ewe lamb below turned grey all over her body as she matured - her head and legs stayed black.
As with all of the other patterns, "grey" can be black based or brown based. Brown based, grey patterned sheep are often called "grey-brown" or if they're Shetlands, they're called "musket". The Shetland lamb below is part way through her transformation from dark lamb fleece to light adult fleece. Notice that although her face and legs stay dark, the wooly areas of her head are light.
An adult Agg sheep has a blend of white and black fibers that make the sheep look "grey". Whitehall Daniel, the beautiful Gotland ram below is one of the UK Gotlands who is being used in the North American Gotland upbreeding program.
There have been Shetland sheep identified as solid grey in color - not a mix of black and white fibers. Let's hope we don't have to deal with those genetics, too! A great information site for all things Shetland, including color genetics, is the "Shetland Sheep Information Site".
What might an Agg/Ab sheep look like? The sheep in the photo below, courtesy of Tongue River Icelandic Sheep, has a very ghostly look. Notice the characteristic badgerface patterning to the head, and the rich tan on the legs. As an adult, this sheep will probably have little of the dark neck/chest and groin stripe left. (This is a purebred Icelandic sheep, so would be Ag/Ab, not Agg/Ab.)
The next lamb is a half Gotland-half Icelandic sheep. Though more difficult to see, this lamb is Agg/Ab. It is also spotted - another set of genes that I'll discuss next. The white head and leg spots cover up some of the katmoget markings. Enough markings are visible to positively identify the Ab in this lamb, especially note the rich tan on her face and legs that is characteristic of the badgerface pattern. Since the sire was Gotland - he contributed Agg, the other half of this lamb's pattern genetic code.
Those are the 6 (or 7 if you're counting Agg) patterns that should be important to the Gotland upbreeding program. To recap:
|White||All over solid white, sometimes with tan||Dominant over all other patterns.||AWt|
|Badger Face||Light upper body, dark lower body. Light and dark areas on face and legs. Prominent tan.||Badgerface, Mouflon, English Blue, Grey all co-dominant||Ab|
|Mouflon||Dark upper body, light lower body. Light teardrops, light under chin. Prominent tan on legs.||Badgerface, Mouflon, English Blue, Grey all co-dominant||At|
|English Blue||Light teardrops, various shades of grey and often light muzzle||Badgerface, Mouflon, English Blue, Grey all co-dominant||Abl|
|Grey (Gotland Grey)||Dark face and legs, solid grey (black - or brown - mixed with white) body||Badgerface, Mouflon, English Blue, Grey all co-dominant||Ag (Agg)|
|Solid||All one color - often sunbleached on tips||Recessive to all other patterns.||Aa|
The next page discusses the "Spotted" portion of sheep color.
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