Can i just ask for some advice ?
A member of a breed club told me to check that a breeders stock was all 'A' tested and not to take a pup from a 'B' or 'C' bitch or dog ,  yet a breeder told me that she doesn't mate 2 carriers .
Can someone please explain ?

So long as one parent is tested optigen clear (A) then none of the resulting puppies will be affected :)

A clear mated to a carrier will produce 50/50 carrier/clear litter

A carrier mated to an affected will produce 50/50 carrier/affected

A carrier to a carrier will produce 25% clear,50% carrier, 25% affected

this means that two carriers should never be mated together and affe4cteds of course should not be bred from, except maybe in extremely rare breeds where an affected could be mated to a clear producing all carrier offspring which in the next generation can be mated to clear, and then the best clear offspring kept. 

It isn't wise or desirable to immediately remove all the carriers from a population as this will reduce the gene pool unnecessarily.  Judiciously used their good genes can be retained and their clear offspring them kept for future breeding.

Thanks for your replies .
If 'A' is a pass , what does 'B' and 'C' mean ?
Also , why are some dogs' patellas certified and some aren't ?  

"B" means the dog is a carrier

"C" means they are affected

Re Patella's and elbows, not all breeds have a problem in these areas.  If you tested every breed for every problem that exists it would never end.

Certainly all or most breeds should be hip scored and eye tested after that it becomes more breed specific.

Thanks for your replies .