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Genetics question help?(4 Posts)
I'm looking for a second dog.
I came across an advert for puppies which seemed great; KC reg, live in house, contract states pups must be returned to breeder if it doesn't work out etc.
I've just been looking on the website, at the breeding bitches and dogs..
All the dogs bar one who appears to be positive (+/+) appear to be carriers for MDR1 +/- and most of the dogs and bitches are clear/ carriers for CEA except a few who are clear and one bitch where it says 'eye test - eyes mildly affected.
Correct me if I am wrong, but doesn't the eye test 'mildly affected' mean that if bred from at least some of this bitches puppies will be affected for CEA?!?!
Is that right?
I'm just a bit staggered and confused.
Should I keep looking or have I got it wrong and this is all okay?
By clear / carrier I mean they don't have symptoms of CEA but carry the gene for it.
Incase that wasn't clear
The bitch who is ‘mildly affected’ must have two copies of the relevant abnormal gene as CEA is a simple recessive condition. If she were bred to a clear dog then all the pups would be carriers but none would be affected. If she were bred to a carrier then each pup would have a 50% chance of being a carrier and a 50% chance of being affected. If bred to another affected dog then all the puppies would also be affected.
The effects of CEA can vary hugely, in its mildest form it may have little to no impact on a dog’s vision but at its most severe it causes blindness and this aspect of it isn’t predictable. A ‘mildly affected’ dog can, if bred to a carrier or similarly affected dog, can produce puppies who are affected much more severely.
It is a positive that the breeder is DNA testing their dogs as minor changes in the eyes due to CEA can be much harder to detect with eye screening in adults, which is why litter screening is recommended in breeds with the condition. If a breeder is relying solely on eye testing adults (which it seems many do, despite the availability of the DNA test) then it’s possible for affected adults to appear to have normal eyes and end up in their breeding programme.
Ideally carriers would only be bred to clear dogs and affected puppies would be prevented and this would potentially be possible in breeds with a very low incidence of the condition. In some breeds, however, the condition is extremely prevalent and it would be impossible to maintain the breed population whilst not producing affected dogs. Obviously the logical step in this situation would be an ongoing outcross programme to increase the number of genetically clear dogs within the population but resistance to breeding outwith the current closed stud book system generally remains pretty high amongst breed enthusiasts.
This website is worth a look if you’ve not already seen it. It was first published quite a while ago however I believe all the information on it it still up to date.