Ask A Scientist© Veterinary Topics Archive

 
name        Stevie  Polce
status       student
age          14

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?
-----------------
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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