Wild Valley Damara are getting into the science of genetic testing! We are going to test all the flock — and use this to help make excellent breeding choices into the future. First — let us be clear — we are not experts on genetics or genetic testing, and that’s exactly why we are talking with the actual experts. What we have found out so far however is exciting for the flock and the breed, and we want to share what we have learnt and why we are taking this path.
In essence, full siblings inherit 50% of their DNA from each parent on average — but which 50% is random, as each chromosome is shuffled before being passed on, so even twins end up with different selections of their parents’ genetic material. In practice siblings share roughly 40–60% of their DNA, and as sheep twins are almost always fraternal, this means that genetically they’re just regular siblings who happened to arrive together. As such, two twin ewes differ in actual inbreeding level, colour genetics, growth rate and more.
This variation compounds over generations. By generation 6, an ancestor that should theoretically contribute 1.5% of the genome might actually contribute anywhere from 0% to 4%+ in a real animal. Some ancestral contributions get amplified by chance, others disappear entirely — and for a small, closed population 5 plus generations in, this is significant. Two animals that look unrelated — different sires, different dam lines — can end up carrying identical stretches of DNA from the same founder animal, or carrying stretches that are quite distinct.
The technical term (we are told) is identity by descent — two animals carrying the same genomic segment traceable to the same ancestor. In a small population the number of truly independent genomic segments available shrinks each generation as some get lost and others proliferate — and after 5–6 generations in a population of smaller size, the effective genetic diversity can be considerably lower than recognised. This is obviously extremely concerning – however the flip side of is quite hopeful. Because the shuffling is random, some sheep will have captured a more diverse cross-section of founder genetics than their pedigree suggests — carrying rare or very underrepresented segments that others in the flock have lost. Those animals are valuable for the flock and breed’s future, and without genomic testing you simply can’t identify them as they look like any other animal on paper.
We are hoping that by undertaking this process we will map the actual current position of our flock, our actual kinship relationships and be able to make more careful breeding selections than ever before. Check in for updates on the process as we begin, we are excited to see it in practice and if it can deliver the data we want!
WILD VALLEY DAMARA 