MVAF

In collies that's true, but not in border collies where only 4-5% are carrying the MDR1 gene. So in principle one does not want to heavily reduce the gene pool to eliminate a single genetic defect, but MDR1 -- which is cruel and highly limiting -- CAN be eliminated while retaining over 95% of border collies in the breeding pool.

Whoa. In humans, a mutation at this gene site can cause both cortical degeneration AND Alzheimer's. This may be worth exploring for the scientifically-literate BC people. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0043728

Apparently, you can have the gene and not be particularly bright. Fruit flies and frogs have a homolog. https://www.ncbi.nlm.nih.gov/gene/488048

https://ghr.nlm.nih.gov/gene/CTNND2#location

Don't buy a puppy unless both parents are Normal/Normal. Neuter all carrying mutant genes. Virtually no problem has a simpler solution. Not that it is easy -- people are great at denial. I lost a sheltie once to the Mdr1 mutation -- and an overzealous vet who used ear mite medicine without asking.

It is a traumatic and debilitating for a dog to live with detached front dewclaws, unless you have an unheard of veterinary surgeon who has invented a means of re-attaching FIVE tendons in working order. Not cool to do this to a dog. Rear dewclaws are sometimes so barely connected that they do pose an injury risk for an active dog.