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I hold my hand up to that error Eva and have removed my reply. It was done in all innocence as I'd been asked several times who my bitch's dam was by .. nothing was implied by association and apologies to that dog's owner is offence was taken .. it seems to be that there could be too many variations to ever lay blame .. thank you for pointing it out.
My dogs' results are on SOEISC .. and yes .. let's test and find the current and future clears to get this beautiful breed that I've loved and owned since 1979 back on track ..
Mel, as I understand it (please someone correct me if I'm wrong for Heaven's sake!), as the gene for rcd4 is an autosomal recessive, then an affected dog must have inherited one gene from each parent. This can only mean that both parents are carriers.
If people are sensible, the carriers will still be able to be used as will affected as long as they are mated to clears & all the progeny tested. You could mate carrier to carrier but the maths may not work in your favour!!
That way, no breeder will lose their treasured lines & the gene pool will not be so badly reduced. But people need to be sensible...
This might help. This is an extract from our article on Autosomal Recessive Genes on the SEISC website which has been "approved" by Jeff Sampson.
Breeders using the rcd4 DNA test will be sent results identifying their dog as belonging to one of three categories. In all cases the terms ‘normal’ and ‘mutation’ refer to the position in theDNA where the rcd4 mutation is located; it is not possible to learn anything about any other region of DNA from the rcd4 DNA test.
CLEAR:these dogs have two normal copies of DNA. Clear dogswill not develop PRA as a result of the rcd4 mutation, although we cannot exclude the possibility they might develop PRA due to other mutations they might carry that are not detected by this test.
CARRIER:these dogs have one copy of the mutation and one normal copy of DNA. These dogs will not develop PRA themselves as a result of the rcd4 but they will pass the mutation on to approximately 50% of their offspring .We cannot exclude the possibility that carriers might develop PRA due to other mutations they might carry that are not detected by this test.
GENETICALLY AFFECTED:these dogs have two copies of the rcd4 mutation and will almost certainly develop PRA during their lifetime. The average age of diagnosis for dogs with rcd4 is 10 y, although there is considerable variation within the breed.
May I add to your statement that it seems not every dog who has 2 copies of the gene will develop the condition. Dogs have been known to live to a ripe old age and gone blind but from cataracts not LOPRA. Equally there are dogs who have gone blind and been diagnosed with LOPRA at a very young age, so it does seem to be very volatile. If the AHT are to be believed and we have 40-50% carriers in the breed then we must have, at some stage, bred carrier to carrier. Would we not then have produced more blind dogs? Could there be an incomplete penetrance? I welcome your observations.
I do also think that statistcs can be misleading and should be taken with a pinch of salt. We assume that a carrier/clear mating will produce an approx 50-50 split but I know cases of CLAD litters where the split was 80% clear and vice versa. The same can happen in carrier to carrier litters. Testing individuals is the only way to be totally sure.
Sorry - the extract I gave you is in fact from the AHT. What I meant to quote from was the article on Autosomal Recessive Genes which is also her http://www.seisc.co.uk/pra-rcd4
on our site or you can find it on ISHI
Carier to carier is not the way to go, that is taking one step back but the others carriers and affected can and should only be mated to a clear...and then in three generations this will be irradicated...not long in the scheme of things. But never put a carier to carier, you will get some affected..not a good way to go...
I appreciate that this mating might not work in favour of the breeder....The problem with a carrier to carrier is that you will produce Affected...what are you going to do with these puppies???...sell them to the public? or put them to sleep?...I for one wouldn't be happy producing an animal that might go blind at some stage in its life, having one that did so...but all the other combinations you will not produce affected and then the problem will not arrise...provention is better than cure...because the cure could be heartbreaking...
I for one lost all my lines in the 70/80's so I know what it is like to lose all those years of work...but this was the disisons that I felt should be taken..and for the health of your puppies it won't be easy...but there will be plenty of good quality clear stud dogs arround, in the future
just re read this and the statment ''but all the other combinations you will not produce affected''
What I should have said was Clear to Affected. Clear to Carrier and of cause Clear to Clear.....these combination will not produce Affected....
What I mean is.....if you have an affected dog (dog 1)...mate her to a clear dog this produced 100% carriers (dog 2)....you mate this bitch to a clear...this will produce 50% carrirers and 50% clear, counting your first bitch this will give you a clear aimimal after three generations (dog 3)....this I have been told is the way forward and hope that we all do not have to go down these lines and we are mostly lucky enough not to have to take 3 generations.
I have had learned over the past few years of having a blind dog myself how all of this works. The basic genetics that is
The 50% of carriers & 50% clear is only a statistical average - Nature is not so obliging as to always split a litter this way & doesn't deal in statistics.