That is too simplistic of a statement to be truly factual. While it is true that dogs closely bred are more inclined to pass on some genetic problems, purebreds wisely bred, will also be free of many genetic problems. I took genetics too and your statement is a favorite thing the profs like to pass on but it is not completely accurate. It comes from the fact that if 2 same breed dogs carry a recessive and a dominant gene for a disease state it can result in them each being carriers but not exhibiting the disease/defect. If they mate with other breed dogs that do not carry the recessive genes, no problem -- disease free mutts. But if they do mate with each other, then you could get two recessive genes together that would result in a diseased pure bred (you could also get two of the dominant genes, or a recessive/dominant combo that would be disease free).
I am not aware of any genetic digestive problems that yorkies are more prone to than mutts, but let's take a condition like luxating patella. Yorkies (and other toy breeds) are more prone to this condition. If yorkies with this condition in their history are bred, they have a high liklihood to pass it on. But if a wise breeder spays and neuters any dogs who have produced offspring that have shown this condition, their breeding program will be less likely to produce the problem.
It is impossible to say purebreds will have more of any kind of problem than a mutt when a mutt by virtue of its definition is a dog of mixed parentage. If that mix is even partially the same as the purebred, then they will both be passing on many of the same genetic traits. See what I mean? The mutts may also be passing on traits that a purebred breeding program would have bred out by selective breeding and spaying and neutering any dogs they feel will pass along poor gentics.
As you get into the genetics course you will find there are so many factors that can affect diseases that have a genetic component, that simply saying purebreds are more likely to have digestive problems than mutts is impossible. It is not even just a simple matter of recessive and dominant genes. There are also modifiers to contend with and not all diseases are single gene defects, so it can really become complicated. More complicated than my memory could dredge up! LOL!
I really wish I could retake a genetics class now that I have something I could relate it to. I hope you enjoy the class and maybe you will be able to apply it to Yorkie breeding. But don't let your professor over-simplify to the point he is diminishing the purebred breeding initiatives. |