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Dog Breeds and Interbreeding
Name: Steve Polce
Status: Student
Age: 14
Date: 11/27/2004
Question:
How does interbreeding dogs hurt the dogs?
Does breeding dogs with their parents or their siblings hurt the
offspring? what effects does it have?
Replies:
Although you are asking specifically about dogs, the answer to your question applies to almost all living species! It is also a very complicated question and to answer it properly would require you to have a college degree in genetics!!! So, I will try and simplify this as best as I can...
Genetic diversity is favored in the natural world. Every animal carries 2 copies of its genetic code in the form of DNA. The way the coding system is designed, an animal can have an disease or disability built in on either copy of the DNA. An animal will not show signs of most diseases and disabilities unless both copies of their genetic code carry the disease/disability. In other words, an animal can carry on one copy of its a disease/disability and not show it.
When animals mate, the offspring obtains one copy of its genetic code from its mother and one from its father. The less related the parents are, the less likely they would both carry matching copies of a disease/disability, the less likely an offspring will inherit the disease/disability, and the less likely the offspring will even be a carrier of the disease/disability. And the more related the parents are, the more likely the offspring will carry or obtain the disease/disability.
Here's a really simplified picture of what I am trying to explain... A mother dog has the following genetic code: A, X where A is a strand of DNA which does not code for a specific disease/disability and X is a strand of DNA which does. Her offspring will inherit either strand A or strand X. In order for the offspring to be a carrier, they have to carry strand X. In order for the offspring to obtain the disease/disability, they have to carry to copies of strand X.
Let's say she mates with an unrelated male which does not carry the disease/disability, and we'll call his strands of DNA strand R and strand S. Their offspring could inherit any of the following combinations: AR, AS, XR, XS. That is, there is a 50% chance her offspring will be a carrier, but NONE of her offspring will come down with the disease/disability.
Let's say she mates with a related male which is also a carrier of the diesase/disability, and we'll call his strands of DNA strand B and strand X (where, again, X carries the disease/disability). Their offspring could inherit the following combinations: AB, AX, XB, XX. That is, there is a 75% chance their offspring will be carriers with the disease/disability, and a 25% chance their offspring will contract the disease/disability.
Let's say she mates with a related male who has the disease, so he carries 2 copies of strand X. Their offspring could inherit the following combinations: AX, XX, XX, XX. And now ALL of their offspring will be carriers, and there is a 75% chance the offspring will inherit the disease/disability!
This is what happens with inbreeding. AND the more inbreeding you have, the more it perpetuates the disability/disease! Unfortunately there is tons of this that goes on in the dog breeding world, and that is a lot of what keeps veterinarians in business! On the bright side, there are many breeders who are working to increase diversity in their animals and hopefully elimate the diseases/disabilities those breeds are known for!
Hope this was clear and answers your question! If you are confused, your science teachers should be able to help you sort this out some more!
Saundra Sample
DVM
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Update: June 2012
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