I thought this was interesting although I'm confused as to why they say all dogs from merle x merle are unable to be registered and then they go on to mention shelties, beaucerons, and dachshunds specifically. Anyone understand what they mean by that? (I've bolded the lines confusing me)
Merle to merle mating in dogs
Following a recommendation from the Dog Health Group, the General Committee has agreed that, with effect from 1st January 2013, the Kennel Club will no longer accept the registration of any puppies for any breed that are produced as a result of mating two merle (dapple) coloured parents together.
The merle mutation is a dominant mutation that causes the characteristic merle or dapple colour pattern in a number of breeds. It is also known that there can be associated health risks in those dogs that have the merle mutation.
Many breeds have lived with the merle gene in their population and have avoided merle to merle matings for many years. Some breeds have successfully requested formal banning of such matings and the Kennel Club will not now accept any litter for registration where both parents are merle for Shetland Sheepdogs, Dachshunds (all varieties) and Beaucerons (although these are called tricolour).
In the breeds where merle is proven to not occur naturally, the Kennel Club will not register any dogs that are merle coloured – these include Chihuahuas (Long and Smooth), Staffordshire Bull Terriers, Bull Terriers and Bull Terriers (Miniature). In addition, the Kennel Club will not register litters from Chihuahuas where one parent is merle coloured.
Merle patterning, patches of lighter colour appearing in the coat, is the result of the M gene in the dog. There are two alleles of this gene: MM (merle) and M+ (non-merle), with merle (MM) being dominant to non-merle (M+). In some breeds, the effect of the merle allele (MM) is termed ‘dapple’.
Unfortunately, the effects of the merle allele (MM) are not confined to coat patterning and we know that there can be an increased risk of impaired hearing and sight associated with it, particularly in dogs that are homozygous for MM (dogs that carry two copies of the MM allele).
Due to the associated health concerns, it is not believed that serious breeders would intentionally mate a merle to merle but the commencement of this restriction in January 2013 allows breeders time to readjust any planned breeding programmes.
I think this is a very good thing.