Yorkshire Terrier coat color thread.

[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!

[Marhcarter]

Who knew we would be getting such and advanced course in genetics on a dog forum! I think it is very interesting and I am learning a lot and remembering stuff from college 20+ years ago...teehee...I think I'm paying better attention this time...

[chachi]

Wow that is a hot mess. We used to have alot of parti breeders on here i wonder what they would say about that

[chachi]

How is it that the Akc missed this when they said partis, goldens and chocolates are yorkies purebred

[pstinard]

Originally Posted by chachi

How is it that the Akc missed this when they said partis, goldens and chocolates are yorkies purebred

They may have made that determination before the DNA evidence came out. I can understand the AKC waiting until the MARS test has become more accurate before using it in their determinations of breed purity, but analysis of individual genes is much more precise. People interested in the purity of the Yorkshire Terrier breed (and who have clout) might want to bring these more recent findings before the AKC to see if they will change their mind. As more and more of these kinds of studies are done, it will be harder for them to ignore.

[KendraE]

Interesting! While your researching, throw in the dd gene! Save me some work!

[pstinard]

Originally Posted by KendraE

Interesting! While your researching, throw in the dd gene! Save me some work!

That is the dilute (Blue Born) gene! We had another thread with the genetic discussion--I'll try to find the links again and add them here. The other discussion started out about the health of Blue Borns. The conclusion was that not all Blue Borns will have health problems, but it greatly increases the likelihood of debilitating skin problems and hair loss. There is a genetic test to determine which dogs are carriers, so they can be spayed or neutered and kept out of breeding programs. Now let me find the links...

[pstinard]

Here is a summary of what I found on dilute (Blue Born) color:

DNA testing labs that test for the "D" locus and can determine which dogs are carriers of the "d" (recessive Blue Born) allele:

VetNostic Laboratories - Veterinary Genetic Testing - Yorkshire Terrier testing

D Locus

Recent research article on the association of the dilute (Blue Born) trait with Color Dilution Alopecia (hair loss and skin problems):

I was able to find an excellent review article from 2007 that discusses known coat color genes in dogs. Here is the citation:

"Genes affecting coat colour and pattern in domestic dogs: a review," by S. M. Schmutz and T. G. Berryere. 2007. Animal Genetics 38:539-549.

At that time, they had determined that Color Dilution Alopecia was due to a mutation associated with the MPLH (melanophilin) gene. Interestingly, not all dogs that had a mutation in that gene had alopecia (baldness) and other skin problems, so it might be a particular kind of mutation in that gene, or a mutation in a nearby gene on the same chromosome that is responsible for the skin and hair problems. In other words, the good news is that not all Blue Yorkies will necessarily become bald. On the other hand, at the time time this article had been written, they didn't have everything figured out. Here are some brief quotes from that article, then I have to get back to work. I'll try to find some more recent articles later.:

The melanophilin gene

"Many dog breeds have individuals that are grey or dilute in coat colour (Fig. 1i,j). However, blue is used to denote other phenotypes in various breeds. In some breeds, these blue individuals are born grey, whereas in other breeds individuals take several months to turn from black to grey. The latter characteristic was referred to as ‘progressive greying’ by Little (1957) and attributed to the G locus. In some dog breeds this is called ‘silver’. A few dog breeds have both types of grey occurring. Some Great Danes and all Weimaraners are born blue or dilute whereas Kerry Blue Terriers (Fig. 1k) and Old English Sheepdogs are born black and lighten as they grow into adulthood. Both of these inherited traits cause modification of both eumelanin and phaeomelanin pigmented areas to a paler shade, although the phaeomelanin change is not as dramatic as the eumelanin dilution. Fawn dogs with a melanistic mask (Schmutz et al. 2003a) are easier to observe because their mask is grey instead of black. Dilute fawn dogs have charcoal instead of black nose leather and pads (Fig. 1j). Dogs with an e/e genotype at MC1R (Newton et al. 2000) or clear red phenotype, such as the two Beagles in our previous study (Philipp et al. 2005) were very difficult to detect as dilute. Dogs that are brindle and dilute, such as some Whippets and Greyhounds, have grey stripes on a pale fawn background. Dogs, such as Weimaraners, that have two copies of the mutations in TYRP1 causing brown (Schmutz et al. 2002) and two dilute alleles are a pale brown. The nose leather and pads of such dogs are a similar pale brown. In some breeds such as Chinese Shar-Pei, the dogs are called lilac and in Doberman Pinschers, they are called Isabella."

"Recently, we reported that Doberman Pinschers, German Pinschers, Large Munsterlanders, and Beagles with a dilute phenotype, co-segregated with specific haplotypes of melanophilin (MLPH) (Philipp et al. 2005). A mutation in exon 2 of MLPH causes a splice junction problem in homozygous mice of the leaden phenotype (Matesic et al. 2001). The last seven amino acids of exon 2 are spliced out in leaden mice because a C-to-T transition introduces a premature stop codon. A human infant was reported to have Griscelli Syndrome Type III due to a R35W mutation near the end of exon 2 (Ménaschéet al. 2003). The hair colour of this child was not reported but this syndrome is considered a form of albinism."

"We have now extended our study of MLPH to include approximately 20 dog breeds. Although a mutation that co-segregates with blue in some breeds has been found (unpubl. data), no single mutation has been found that explains the blue in all these breeds. A couple of common mutations occur only in blue dogs (unpubl. data). Our study to identify all the alleles causing blue is ongoing."
-------------------
Diseases associated with pigmentation

"Some (n = 30) of the 119 grey/blue dogs we studied (unpubl. data) showed evidence of hair loss and much more rarely skin problems, symptoms typical of colour dilution alopecia (CDA) and black hair follicular dysplasia (Schmutz et al. 1998; von Bomhard et al. 2006). This was not true of all adult blue dogs however. The symptoms also appeared to vary by breed with the Large Munsterlanders displaying complete hair loss in all grey areas by 12 weeks whereas most dogs of other breeds were a few years old before this degree of hair loss occurred. Several dogs 5 years of age or older were reported to have no hair loss or skin problems. Several of the dogs were pups or <2 years of age or had large areas of white fur and therefore we could not determine whether these dogs had or would develop CDA. Dogs that were blue or blue fawn, male or female, long or short-haired and with or without white spots were affected. There may be a slight tendency for earlier symptoms in dogs with longer hair. CDA was reported in 26 of the 100 dilute dogs with a T/T genotype and four of the 19 dogs that showed a dilute phenotype but did not have a T/T genotype at the synonymous c.106C>T polymorphism in exon 2 of the MLPH gene (unpubl. data)."

"Not all ‘blue’ or genotypically d/d dogs (Fig. 1i,j), have problems associated with CDA and not all dogs that have symptoms develop them at a similar age of onset or with similar severity. For example although all Weimaraners are dilute and all of the eight dogs of this breed we studied had a T/T genotype, not all had CDA. Laffort-Dassot et al. (2002) likewise described variable symptoms in five Weimaraners. Miller (1990) suggested that there were possibly multiple recessive alleles of the dilution gene. Although this may be true, it does not appear that dogs with and without CDA necessarily have different mutations in MLPH. Since MLPH binds to RAB27A in the region (Strom et al. 2002) where we have identified some mutations in MLPH, we wanted to determine if a mutation in RAB27A might interact and cause some dogs to experience symptoms of CDA whereas others did not. We sequenced the entire coding region of RAB27A (GenBank DQ494380) in a Large Munsterlander that had severe symptoms of black hair follicular dysplasia, an Italian Greyhound with CDA symptoms, and a black-and-white Large Munsterlander and a chocolate Labrador Retriever which were not dilute and had no symptoms. No polymorphisms in the RAB27A sequence were detected."

[KendraE]

Thanks! I've read a ton and never stumbled upon that article! Definitely true, not all blues develope CDA. (Well at least so far with my boy, Mack) I do believe however blues have a much lower immune system... I wish there was research on that! I'm always curious to read all research.... If you come across anymore, let me know!

[pstinard]

The color pattern seen in breed standard Yorkshire Terriers of the steel blue body with tan head and extremities is due to a certain mutation at the ASIP (agouti signalling protein) locus, classically called the "A" gene. Yorkshire Terriers carry the variation of the "A" gene called "at." Interestingly, there are four major variations of the "A" gene:

ay = "fawn" or solid golden-brown
aw = "wolf sable" or hairs that are banded black and brown
at = black and tan, with black body and tan extremities
a = recessive black

Interestingly, the order of dominance is ay > aw > at > a, which means that fawn is dominant to all the other color patterns, wolf sable is dominant to black and tan and recessive black, and black and tan is dominant only to recessive black.

There is a variation of black and tan called "saddle tan", which is due to an interaction of the "at" mutation with mutations at other modifier genes. In saddle tan dogs, the tan coloration comes up farther onto the body than in the black and tan pattern. I'm providing three links to research papers describing these interactions that are publicly available in their entirety below. Although neither of these studies specifically examined the DNA of the Yorkshire Terrier as far as I have read (a quick once-through), they postulate that Yorkshire Terriers are actually a form of saddle tan in coloration, with the tan not coming up quite as far on the body as in other saddle tan breeds. Here are the research articles:

A SINE Insertion Causes the Black-and-Tan and Saddle Tan Phenotypes in Domestic Dogs

eCommons - Gene interactions with Agouti Signaling Protein produce complex pigmentation phenotypes in the domestic dog

http://www.eebweb.arizona.edu/Facult..._etal_2013.pdf

[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.

[cindersellie]

Thanks for the update. I find all of this interesting! Glad your here to find the information and explain it to all of us! Looking forward to reading more about this!

[pstinard]

While I'm at it, there is another characteristic of Yorkshire Terrier coat color, and that is progressive greying (as opposed to dark black). Progressive greying is due to a dominant allele at the "G" locus. This gene explains why Yorkshire Terrier puppy coats start out black and progressively turn grey (steel blue or silver blue) over time. This gene has not been cloned yet (as far as I know!), so the underlying biochemical basis for it is not known, nor is there a DNA test for it. Here is a review article that describes a wide variety of dog coat color genes:

http://www.fleetfiretimbers.com/fft/...Review2007.pdf

[pstinard]

More essential reading--a chapter from a recent book on the Genetics of the Dog: Molecular Genetics of Coat Colour, Texture and Length in the Dog:

http://research.hudsonalpha.org/Bars...hapter2012.pdf

[MyGirlSasha]

well whatever causes it, I think its beautiful