Monday, July 9, 2012

Mismark Case Study: Cavalier King Charles Spaniel

According to the AKC, Cavaliers come in four allowable colors, three of which are seen here: Blenheim, tricolor, and ruby. Black and tan is not shown.
The Cavalier King Charles spaniel is a popular pet and is one of the largest of the breeds in the toy group. Though the breed comes in four colors, two are more commonly seen: Blenheim and tricolor. There are also several mismarks, some of which are due to breeding within the allowable breed colors:
  • Incorrect white
    • Too much white on the face of a Blenheim or tricolor
    • Any white on a ruby or black and tan
  • Ticking 
    • On a Blenheim or tricolor
  • Incorrect tan 
    • Seen on tricolors and black and tans 
  • Incomplete pigment 
    • Of the nose or eye-rims on a Blenheim or tricolor
  • Blue eyes 
    • Usually only seen on a Blenheim or tricolor
White on a black and tan
When it comes to incorrect white, both of the forms I describe are really to be expected when breeding for the allowable colors within the breed. The piebald gene (sp), which results in Blenheim and tricolor dogs, is recessive to the solid gene (S) on the Spotting locus. However, in most cases a dog who is heterozygous for these genes (Ssp) and thus carrying piebald will have some amount of white. This is often as little as a bit of white on the chest and/or toes, but this may extend up the chest and even result in some white on the face and tail. The problem is: according to the standard, no amount of white is allowable on ruby or black and tan dogs. This means it is unlikely that the solid dogs are bred to the piebald dogs, leading to color class breeding. This is problematic, as it basically creates breed within breeds, narrowing overall genetic diversity to two smaller pools, and thus raising the potential for problems that result from increased homozygosity. Also, only breeding solid dogs to other solid dogs will not eliminate white markings. It's far from uncommon for a genetically solid dog to end up with some white on their chest and/or toes. This is thanks to normal developmental variation in the womb.

Too much white, lacking pigment
In addition to the above, "incorrect" facial white on piebald dogs is also far from uncommon. Facial white is controlled by as-of-yet unknown modifiers. Selection can favor one form of facial white, but it's almost impossible to eliminate the ones that would be considered "undesirable." Since this is true, dogs with more or less than the preferred amount of white shouldn't be surprises. Also, since selection in Cavaliers favors dogs with rather a lot of facial white, this likely increases the likelihood of a dog being produced that has too much white. In relation to this, dogs with a lot of white on the face are far more likely to lack pigment of the nose or eye-rims, or to have one or more blue eyes. Since the standard favors dogs with so much white on the face, this makes it quite likely that these dogs will appear.

Heavy ticking, too much white
As for ticking, there is a bit of a conundrum in the breed. Some ticking is fine, and a lozenge between the ears, which may or may not be a large ticking spot, is preferred. But, if a dog has too many ticking spots, it's not allowed. So, it's likely that the dogs that are allowed are heterozygous for the ticking gene (Tt) and the dogs that would have too many spots are homozygous (TT). So, why allow ticking at all if you're only going to penalize dogs that have too many spots?

Incorrect tan on the face
Another mismark that is based on normal color variation in incorrect tan markings. Taking the standard as it is stated, any tan on the outside of the ears is not to be allowed and any tan between the marking above the eyes and on the cheeks would also be incorrect. However, these things are not uncommon in tan pointed dogs. This is another case of minor differences being enough to make a dog "undesirable."

All of the mismarks that are seen in the Cavalier King Charles spaniel are really rather minor things that are to be expected from normal canine color inheritance. As such, they are nothing more than silly aesthetic preferences and do not reflect on the quality of the dog. Since this breed is a very common pet and, indeed, bred to be a companion, temperament and health should be far more important than what the dog looks like. Looks should never take precedence over these other, far more important traits. As such, color standards are really rather silly things based on nothing more than minor aesthetic preferences of the few people that wrote the standard. As the differences I have mentioned have absolutely no effect on the quality of a dog, eliminating a dog from the gene pool simply because it does not fit the color standard is ridiculous. Also, as purebreds are bred in closed registries, dropping any dog from the pool of potential mates makes it quite possible, and indeed likely, that a negative loss of genetic diversity will result. Since the color standard has also lead to color class breeding in the Cavalier, this is even more problematic.

Images are from Wikimedia Commons and Flickr.com under Creative Commons licenses: one, two, three, four, five.

3 comments:

  1. Hi – Will you please post a link to your Blog at The Cavalier King Charles Spaniel Community at vorts.com? Our members will love it.
    Members include: CKSC Owners, Breeders, Rescues and Lovers.
    It's easy to do, just cut and paste the link and it automatically links back to your website...
    You can also add Photos, Videos, Rescues and Classifieds if you like.
    Email me if you need any help or would like me to do it for you.
    The Cavalier King Charles Spaniel Community: http://www.vorts.com/cavalier_king_charles_spaniels/
    Thanks,
    James Kaufman, Editor

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  3. Excellent tips. Just Awesome. Your post has guided me a lot and this is putting every piece together. Thanks, man.

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