[pstinard]

Originally Posted by pstinard

Hi, I posted this earlier in the Parti vs. Biewer thread, but this article seems to be of enough general interest that it merits its own thread. It describes the nature of Biewer, Parti, and Chocolate coat colors in Yorkshire Terriers:

Here is another fascinating research paper on DNA coat color testing in dogs that specifically references the Yorkshire Terrier:

Coat color DNA testing in dogs: Theory meets practice

It is behind a pay firewall, so I will quote the relevant parts:

These data illustrate that owners may be using coat color testing to help them understand the appearance of pups of unexpected coat colors in their litters. Using DNA testing will therefore help them to eliminate carriers of undesired alleles from future breeding. However, in some cases, dog breeders are actually trying to create a line of dogs with a new coat color. An example of this is the Biewer Yorkshire Terrier, where random white spotting caused by a SINE insertion in MITF [11], is now selected for. The presence of the e allele in 9 of the commercially tested Yorkshire Terriers (Table 1), suggests that the random white spotting, called particolor in this breed, has likely been introduced from a breed where the e allele occurs commonly.

So according to this study, Biewers carry the piebald ("sp") allele at the MITF gene, and Parti Yorkshire Terriers carry the "e" allele at the E (technically called the MC1R) gene. And BOTH were introduced from other breeds, because the likelihood of the exact same mutation arising independently in the Yorkshire Terrier is astronomically small. That article is a GOLDMINE of information, and I am going to curl up and read through it more carefully tonight. It also references people testing their Yorkies for the presence of the "b" (brown, or chocolate) allele at the B (technically called TYRP1) gene, and I need to see if this was introduced from other breeds as well--since they were testing for specific variations of the "b" allele found in naturally brown breeds, it's very likely that chocolate color in Yorkies came from some other breed. What a mess! DNA doesn't lie, folks!

After doing a little more reading up on the "e" mutation, I have found that it is more likely to be responsible for a golden yellow color rather than Parti colored white spotting. Perhaps Partis are piebald at the MITF gene as well. Either way, it still likely was bred into the Yorkshire Terrier from some other breed. Clearly, more coat color DNA testing of all nonstandard Yorkshire Terrier colors needs to be done.