Copyright, 2007
The Gotland sheep is not a rare breed in the world as a whole. There is a healthy population in their native Sweden, and flocks are scattered throughout Denmark, the Netherlands, the UK, Australia, New Zealand, and other parts of the world. In their native country, they've been bred for many generations, essentially "fixing" the genes for color, and creating a sheep that is predictably grey in appearance with or without a few white spots on the head, legs and tail.
In North America, there are no purebred Gotland sheep, and the likelihood of importing live sheep is very low due to expense and government regulations. We can, however, import semen from outstanding Gotland rams in selected countries by following strictly regulated protocols. In 2003, the first Gotland semen was used in North America, and by 2008 a population approaching 100 Gotland cross sheep has been produced. A handful of 75% Gotland sheep were born in 2007 and 2008.
In June, 2006, the Gotland Sheep Breeders Association of North America chose nine Foundation breeds to continue the breeding up process in North America. These breeds were chosen based on their similarities to Gotland sheep. Three North European Short Tailed breeds - the Shetland, the Icelandic, and the Finnsheep - were chosen because of their naturally short tails, similar body types, and similar heritage to the Gotland. Six Longwool breeds were chosen based on the similarity of fleece type - the Leicester Longwool, Border Leicester, Blue Faced Leicester, Cotswold, Wensleydale, and Lincoln. Each of these nine breeds has both Gotland like and non-Gotland like characteristics. All of these breeds bring undesireable color genetics to the gene pool.
Within the nine Foundation breeds, most of the colors, patterns, and spot variations found in wool sheep are present. Within the Gotland breed, there is only one allowed color, one allowed pattern, and minimal spots allowed. All of the allowed Gotland color characteristics can be hidden by color genes present in these nine Foundation breeds. As each generation is bred to imported semen, the probability of the Gotland colors coming forward is increased, however, by understanding color inheritance, some of the reliance on probability and guesswork can be eliminated.
For example, the chance of any one "hidden" gene making it into the first generation is 50%. Into the second generation (3/4 Gotland) the chance is 25%, or said another way, one quarter of the flock will carry the "hidden" gene. In the third generation (7/8 Gotland), the chance of a single "hidden" gene making its way to each sheep is 12.5%, or one eighth of the flock will carry the "hidden" gene. These percentages are based on a single color gene. Color is actually made up of multiple genes; I will be addressing 4 individual genes that are relevent to Gotland sheep in this paper.
When two of these potentially "hidden" genes are considered, each 75% Gotland sheep has a one in four chance of carrying each one. In the flock, one quarter will carry hidden gene #1, and one quarter will carry hidden gene #2. The two groups do not consist of the same sheep. When the statistics are worked through, about 50% of the flock will have no hidden genes; 3/16ths will carry hidden gene #1, 3/16ths will carry hidden gene #2, and 1/16th of the flock will carry both hidden genes. Only 9/16ths, or just over half, of the flock will be clear of the two hypothetical "hidden" genes. To rephrase that, when you consider two individual genes, only approximately one half of the flock will be "clear" of hidden genes in the second generation. As the number of genes under consideration increases, less and less of the flock is "clear" of hidden genes.
The good news is that you can easily select away from hidden genes, and make progress much faster than these examples indicate. By understanding a little about color genetics in sheep, you can also avoid inadvertently choosing colors and patterns in your flock that will be difficult to manage.