Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne 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


Click here to return to the Veterinary Topics Archive

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory