Copyright, 2007
For many generations Gotland sheep in other parts of the world have been selected to be GREY. All over the world they're known as grey sheep. There is even a "color" gene (now we know it's a pattern gene) that is named Gotland Grey. They have been bred as grey sheep for long enough that we can assume several things about their genotype:
The basic color of Gotland sheep is Black - BB/BB
The basic pattern of Gotland sheep is Grey - Agg/Agg
Gotland sheep can be spotted or not - SS/SS, SS/Ss, or Ss/Ss
Gotland sheep are not Extension dominant - E+/E+
Add these together and there are only 3 possible color genotypes for Gotland sheep: BB/BB Agg/Agg E+/E+ SS/SS or BB/BB Agg/Agg E+/E+ SS/Ss or BB/BB Agg/Agg E+/E+ Ss/Ss. Obvious from the photo of the UK flock of Whitehall Gotland ewes below is that there are other modifying genes at work, allowing for light and dark shades of grey, varigation in the fleece, "whiteness" of the white fibers. Aren't they beautiful?
We, in North America, should be working toward the homozygous (gene pair is composed of the same two genes) conditions - black, Gotland grey and non-extension dominant. Spots? Well, I'm going to work on small head, leg and tail spots - or no spots - hoping to keep the nice, clear, solid, blue-grey fleece.
Of note is that any obvious pattern (Ab, At, Abl) is a disqualification - these other pattern genes displace Agg. White, brown, and black sheep are disqualified, as are sheep with large white patches in their wooled areas. These disqualifications are listed in the GSBANA breed standard. Sheep with these color variations are not allowed to be GSBANA Registered, although they can be Recorded in the flock book and used in the breeding up program. If you have these color variations in your emerging Gotland flock, this paper can help you identify how to eliminate them and achieve the homozygous Agg/Agg BB/BB E+/E+ sheep.
In Gotlands, the four gene pairs we've been discussing are inherited separately. While it is theoretically possible that every single gene is inherited separately, there is plenty of evidence that groups of genes are inherited together. It is entirely possible that other wool characteristics could be inherited with ... say... the Agg gene. This could be a good reason to try and concentrate the Agg from the Gotland sires in the North American flocks. Well, what does that mean? How can you be sure the grey is coming from the Gotland sire when there is age-greying and plenty of Ag grey in the Foundation breeds? Ahhh, that is my secret formula!
We at EverRanch plan to use the pattern gene to "filter" in homozygous Agg. Many of our upbreeding sheep will be white. Why white? Remember that every sheep has exactly two copies of each gene. Agg is inherited at the pattern locus along with white (and mouflon, badgerface, English blue, grey, and solid). If a lamb out of a Gotland sire is white, its pattern is Agg (from Dad) and AWt (from Mom). Now, when that white AWt/Agg sheep is mated to another Agg/Agg Gotland sire, it's offspring will be either AWt/Agg (white) or homozygous Agg/Agg (Gotland Grey) - both pattern genes coming from the Gotland sires.
A similar case could be made for using At, Ab or Abl, but not Ag or Aa. Ag and Agg are indistinguishable, so you could not tell by looking if the lambs were Ag/Ag or Agg/Agg, or even Ag/Agg, not to mention Aa/Agg or Aa/Ag. An aside - in Icelandic sheep, the heterozygous Ag/Aa sheep are a deeper shade of grey than the homozygous Ag/Ag sheep. If the same is true in Gotland sheep, the higher score for deeper grey color would favor Aa/Agg or Aa/Ag sheep - something we do not want in our North American Gotlands.
Could you do the same thing for black and brown? Not practically. Because brown is recessive it is difficult to identify, much less breed out. If one was to use all brown foundation ewes, it is possible to eventually lose the brown recessive. It would certainly increase the chances of having 90-something percent brown-grey Gotlands. (I wonder what they'd look like???) I'm not willing to go that route... yet. It is interesting that our best fleeced half Gotland lamb is out of a brown Shetland ewe.
How about E? Could that be filtered to be all from the Gotland sires? I haven't yet thought of a way to do that. You'd have to identify ED/ED sheep to start with, or take the colored offspring from a Gotland to an ED Foundation ewe who was also AWt/AWt. Hmmmmm. With spots, you could start with non-spotted sheep that you assume don't carry spots, and breed to Gotlands with spots, you could select all the spotted sheep. At that point their S genes should be from the Gotland sires, and you could start using Gotlands with or without spots. The problem comes with identifying the very specific genetic makeup of these foundation ewes.
So, theoretially, the ideal case would be to locate and identify the genetic opposite of Gotland grey sheep for foundation ewes. That would be a solid brown appearing ewe: ED/ED Bb/Bb AWt/AWt SS/SS. Use a spotted Gotland sire: E+/E+ BB/BB Agg/Agg Ss/Ss. The first AI generation offspring would be ED/E+ BB/Bb AWt/Agg SS/Ss - solid black sheep... perhaps age-greyed. Next AI generation, white ewes would be selected: E+/E+ BB/B(B or b) AWt/Agg SS/S(S or s). Now we've eliminated the extension dominance. Third AI generation, the grey ewes with spots are selected: E+/E+ BB/B(B or b) Agg/Agg Ss/Ss. Oh! We've got everything selected except there's that pesky recessive brown gene left possibly hiding for many generations. ...now to find those elusive solid brown, extension dominant ewes! Writing this, I've realized that maybe, just maybe, those ewes exist! And maybe I'll keep my eyes open for them. Until then, we'll be using the "white filter".
The next pages have a few puzzles to stretch your mind.