Page 336 - The Complete Dog Breed Book Choose the Perfect Dog for You, New Edition (DK)

336 C ARE AND TR AINING

Inherited diseases for breeding carefully. Good breeders will be able to go back
An inherited disease or disorder is one that is passed from through several generations to tell you whether any of the
one generation to the next. Such a disease can mean that an dogs in their breeding lines have had medical problems. They
individual is born with a medical condition or is genetically will also know what, if any, conditions remain a potential
predisposed to developing one in later life. In the case of source of concern in the puppy of your choice.
dogs, there are conditions common to each breed that are For many conditions, especially those with a simple
known to be inherited. These include joint disorders, recessive inheritance pattern (see box below), screening
blindness, and deafness. Responsible breeders do all they tests can be carried out. Ask your breeder to show you the
can to make sure that dogs affected by these disorders are results of any tests that are relevant to your puppy or his
neutered to prevent them passing on their genes to the next parents. If one of the parents is a carrier, then their puppies
generation. Nevertheless, the nature of inheritance means may be, too, so it would be unwise to breed from your dog
that these conditions can never be eliminated completely, without screening it first. If both parents are carriers, your
because some dogs are carriers (see box below). puppy is at risk of being affected by the condition. Before
Many inherited disorders can be traced through a pedigree you visit a breeder, learn all you can about the screening
and therefore breeders can take steps to reduce the chances tests that apply to your chosen dog and his likely conditions,
of breeding an affected puppy by choosing their bloodlines and make sure you know what results to look out for.
GENETICS AND INHERITED DISEASE

A common way for hereditary CROSS 1
disorders to be passed onto the
offspring is through recessive Sighted Carrier
inheritance. In the example of
congenital blindness, dogs will
be blind if they inherit a RR Rr
recessive gene (r) from both
parents. The diagram shows
how this can happen.
In cross 1, a sighted dog (RR)
is crossed with a sighted carrier
(Rr). All the offspring possess at
least one dominant gene, and as
a result are sighted. However, two Sighted Sighted Carrier Carrier
of the puppies are carriers of the
recessive gene for blindness.
In cross 2, both parents are
carriers of the recessive gene. RR RR Rr Rr
This means that there is a one
in four chance that one of the
puppies (rr) will inherit the CROSS 2
recessive gene from both Carrier Carrier
parents and be born blind;
two puppies will be carriers
(Rr); and one puppy (RR) will Rr Rr
have normal sight.

Sighted Carrier Carrier Blind
Key
R = Dominant gene
for normal sight
r = Recessive gene
for blindness RR Rr Rr rr

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