Showsight - November 2021


Trea Kroeske; her kennel Telgthoeve is in The Netherlands.

THE PROBABILITY OF INHERITANCE The Punnett Square can also be applied to other traits, such as hereditary diseases, like Degenerative Myelopathy, a degenerative neurological disorder. While it may be tempting to toss carriers from gene pools, it is not necessary. A Punnett Square can be employed by breeders to illustrate the probability of inheritance in order to avoid producing an affected offspring. For example, if we take a clear dog designated “NN”, and a carrier designated “NC”, and draw a Pun- nett Square, we would see that the odds of producing an affected dog are 0%, with the odds of producing a carrier at 25%. Keeping carriers in a breeding program has the beneficial effect of increasing the size of a breeding population, and keeping genetic variation high in order to avoid other pitfalls that can occur, such as bottlenecking. “Population” is defined in Ecology as a group of individuals of the same species living and interbreeding within a given area. This is an important concept to understand where it concerns purebred dogs. If we replace “species” with “breed” then we immediately understand that we have reduced our “breeding population” from all dogs to just the dogs in that breed. If we understand further that, “…within a given area…” can mean the population of our kennel, of our peer group, of our breed club, of our State, Region, Country… we can see how this population can begin to expand to include more individuals in the population of consideration. When we have the mechanisms at hand, why stop at Country-level? Why not think globally? Bottlenecking generally occurs in a population due to natural events such as droughts, diseases, famines, etc., which act dramati- cally to reduce a population size in rapid proportion. One theory known as the Toba Catastrophe was presented in the 1990s, sug- gesting that our own human species crashed to between just 3,000 to 10,000 individuals worldwide (compared to nearly 8 billion today thanks to the Industrial Revolution). The consequence of a genetic bottleneck, as you may have already concluded, is that it signifi- cantly reduces the size of a population, and subsequently, the genetic variation within the population. Only through mechanics of popu-

lation genetics can bottlenecks be resolved. These include gene mutation, gene drift, and gene flow. While the Toba Catastrophe theory is not without controversy (as with most human evolu- tion theory), it is illustrative of the problems which can occur in species—or breeds of dogs—when genetic bottlenecks do occur. This includes inbreeding depression, which can be particularly detrimental to small populations. Consider a small population of a rare breed in North America if it is cut off, isolated, and highly inbred to maintain “type.” Think back to what was mentioned earlier about “in a given area.” The breeder of rare breeds MUST collaborate, and MUST collaborate far and wide. It is grossly inefficient to say “I must protect my breed and trust no one,” or the fatal flaws of inbreeding depression will be perpetuated.


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