2018 May June

Q&A
Do These Genes Fit?
Send your questions to:
C.A. Sharp
1338 Trouville Ave.
Grover Beach, CA 93433
ph. 805-473-0078
e-mail: 51ca@ashgi.org
Can you please tell me if any lab that you
know is doing a study regarding PRA in
Australian Shepherds? I am told there us
a study out there saying that Australian
Shepherds do not carry PRA in their lines
and that it is only a Mini Aussie/Mini
American disorder due to mixed breeding.
Please explain.
I am not aware of any scientist doing
a study on PRA in Aussies at present.
Aussies do sometimes (it is rare) have
a type of PRA called progressive rod cone
degeneration (prcd). The gene for the prcd
form of PRA was discovered in 2005 at
Cornell University during research on other
breeds. Optigen, Cornell’s commercial
DNA testing lab, offers tests arising from
their research and sometimes licenses those
tests to other labs. Optigen will test samples
from dogs clinically diagnosed with PRA
for free to determine which of the many
forms of PRA the dog might have.
In 2006 a PRA-diagnosed Aussie’s
sample was sent to them. They found it had
two copies of the prcd mutation and started
offering the prcd/PRA test for Aussies in
November of that year. Many labs around
the world have been offering it for a number
of years, though not all offer a licensed
version of the test.
According to Optigen’s CEO, Sue
Pierce-Kelling, they have received five
cases of Aussies diagnosed with PRA by
veterinary ophthalmologists that were
confirmed by DNA testing to have prcd-
PRA. They also have eight samples from
PRA-diagnosed Aussies that do not have
74 AUSSIE TIMES May-June 2018
prcd or any other known form of PRA.
What form these dogs might have has not
been determined. It is possible for a single
breed to have more than one form but at
this point we can’t say that’s the case for
Aussies.
If you are concerned that your dog
might have or carry PRA (signs typically
don’t show in Aussies until the dog is 4-6
years old), get the test.
As for Minis, they do share early
background with Aussies. I used to take a
junior handler to shows with me back in
the 1980s who had an obedience dog that
was 12” and she was by no means the only
small Aussie around from at least the 1970s
– maybe before, too, but I wasn’t involved
then. In the late 1990s and early 2000s Mini
breeders did considerable back-crossing to
smaller Aussies to improve type, so since
the present-day breeds are kissing cousins,
it isn’t any surprise that the two might share
some of the same diseases.
Prcd is the most common form of PRA
and found in a wide variety of breeds. This
indicates the mutation has been around for
a long, long time. Much longer than there
have been either Aussies or Minis.
I saw somewhere you told someone, “They
are both carrying genes for it. It is not a
dominant trait, so two dogs that do not
have it can easily produce it.” Can you
explain this sentence?
Well, it’s a touch out of context and
I don’t recall the specific conversation or
e-mail exchange, never mind what “it” is. I
was apparently responding to someone who
got something they didn’t want out of two
parents that don’t have the trait in question.
Whatever the trait was, it is either recessive
or polygenetic. If a trait is single-gene
dominant it can come from only one parent
but, with rare exceptions, that parent would
have it too. The HSF4 cataract mutation, a
dominant, is one of the exceptions because
it is only a risk factor so not every dog that
has it gets cataracts.
To produce something that is not
dominant – which is the case with the vast
majority of traits you do not see in either
parent – both parents have to contribute
genes for it. If it’s a single gene recessive,
each parent would be a carrier, as with
red color or defects like CEA. If it has
complex inheritance (multiple genes) the
parents’ contributions could be anywhere
from 50/50 to 99/1 but there is no way to
tell for sure how much a particular parent
contributed. Not with genetic science where
it sits right now, anyway.
I’m a budding Aussie breeder with one
litter under my belt. My male is black
and my female blue merle. One of their
puppies was a red merle, which means
that dad is red-factored, right?
Since one was red I decided to keep
her. I won’t breed until after she turns
two but I already got her a mate. My
choice might not have been such a good
one. I thought he was a red tri and the
veterinarian of the breeder listed him that
way, but a DNA test said he’s cryptic merle.
I read on your website that a cryptic merle
with a merle can have double merles. So
now what do I do?
First off, if you got a red puppy out
of a blue and a black then BOTH of them
are carrying red. You don’t get red unless
both parents have at least one copy of the
red version of the gene.
About cryptic merle – merle is a weird
gene that does some unusual things.If
your new boy appears to be a red tri but is
genetically cryptic there is a possibility he
could produce typical double-merle pups
(lots of white, hearing and eye defects) if
bred to a merle or another cryptic. However,
the risk (3%) is low. It could happen but it
probably won’t.