The Importance of Genetic Variety
Dionis MacNair
The loss of genetic variety can have a significant impact upon our native breeds. Nature does not provide parity of sex without good reason and when the ratio of male to female goes below one to thirty all genetic variation is lost in five generations. In ponies that is within about 40 years.
Why should this matter? In-breeding fixes type but reduces adaptability. Circumstances always change, so the ability to react to and adapt to that change is vital for survival.
Mutations within species frequently occur and most of them are insignificant. However some of them can be very beneficial and this is how evolution advances; for example Eclipse was bred from relatively moderate parents but his tracing ability was phenomenal. It was a skill he was able to pass on to his progeny, but his own sire never again sired anything like as good.
Some mutations are potentially catastrophic if there is little genetic variety. A further complication is that recessive mutations can be carried for five generations before reappearing.
The fact that a breed is numerous can be of no help in this situation. As an example from a different species, Holstein cows are very numerous but also have very little genetic variety, and now suffer very badly from lameness. However worse than the lameness, which in itself is a significant welfare issue, more and more frequently they are also suffering from fertility problems, not good news in a dairy cow!