German genetic study on Blue Weimaraners shows mutation unlikely.
For more than 60 years, there has been ongoing debate and speculation on the genetic origins of the progenitor of Blues in America, Cäsar Von Gaiberg or Tell. Was Cäsar a cross-breed or had there been a genetic mutation? Logically, those against the Blues argued he was a cross-breed, a plausible theory supported by the fact that his breeder also bred Doberman Pinschers. The Blue supporters have argued with intriguing anecdotal evidence including witnesses who claim to have seen them in Europe many years ago, and the fact that a Weimaraner Club of America standard before the birth of Cäsar listed Blue as an acceptable shade of gray.
Last year, I got word that there was a DNA research study proposed by a team of geneticists in Germany. They wanted to study the genetic differences between the gray Weimaraner and the blue Weimaraner. They were asking for blood samples from Blue owners. I shipped them samples from Ellie and Bella and another person here in France participated. There were also liaisons with owners in America and a few other countries.
Why did I participate? In Weimaraner forums and email groups, Cäsar’s genetic legitimacy is always the focus of all arguments concerning the blue Weimaraner’s legitimacy. We battle round after round on this subject, unable to move on. I had no delusions that this study would prove Cäsar was indeed the result of a mutation and that the Weim clubs would then accept us with open arms. I just felt that it was time to move past the argument of Cäsar’s legitamacy and start dealing with the present. Any information that helped us to move on—one way or another—would be valuable.
The following article summarizes the results of the genetic research done in Germany.
Quick note: If you are as scientifically challenged as I am, this information can be a bit confusing. To keep this post from getting too big, I will write more in the next post. Just Weimaraners has written an article on the original paper, here.
The original paper was published as:
Tracing the origin of “blue Weimaraner” dogs by molecular genetics.
W.M. Gerding, S. Schreiber, G. Dekomien, J.T. Epplen
Journal of Animal Breeding and Genetics
Article first published online 22 September, 2010
You can read the original paper Here.
This summary was also published in the magazine of the German Kennel Club
VDH: “Zeig mir das Fell, und ich sage dir die Rasse”
W.M. Gerding & J.T. Epplen, Unser Rassehund, 6/2010 p. 32–35
One coat color — one breed?
Wanda M. Gerding & Jörg T. Epplen, Human Genetics, Ruhr-University Bochum, German
The coat color of a dog is an immediately recognizable characteristic, determining the overall appearance. It can often be a defining characteristic in certain breeds. In some breeds, a specific coat color is exclusively observed such as in White Swiss Shepherds or Black Terriers. In other breeds, different color varieties exist, such as in Labrador Retrievers (cream, brown, black and dilute versions of these colors). Sometimes different breeds have very similar color patterns such as black and tan Dachshunds or Dobermans, although their overall appearance is quite different. Needless to say, there are numerous characteristics typical of a given breed. This includes the coat color but also other physical characteristics, such as the shape of the head, the length of the legs, the hair length and texture as well as other properties such as performance, etc. All of these different features determine a breed’s characteristics. In genetics, physical appearance (or certain parts of it) is called the phenotype. For the geneticist, however, the invisible genetic material is of special importance, namely the composition of the DNA. The exact make-up of the DNA in a particular dog is called the genotype. Phenotype and genotype are important aspects of an organism and together make up the individual dog. In recent years, we have investigated relationships between phenotype and genotype, specifically in the Weimaraner breed. In Germany there are two standard variations of the coat: the short haired, and the less common long-haired Weimaraner. The few genetic differences and the many similarities between both hair length types have already been described in the past (Tanja Schrameyer and colleagues published these results in 2005 in a scientific journal #). We recently examined a further genotype-phenotype relationship of the Weimaraner coat color using molecular genetics.
The grey Weimaraner coat color can exhibit several shades. The official breed standard defines the coat color as variations of shades of “grey” — mouse, fawn or silver, which are all dilutions of brown (shades of light brown or tan). The genes involved in the expression of this particular coat color have been previously described, but not studied in detail in Weimaraners. Furthermore, besides the classic grey Weimaraners, “blue” Weimaraners that have a dilute black coat color (also called slate grey by their fanciers) have been bred primarily in North America. Thus, our study had another goal: We wanted to find out, how the occurrence of dogs with “blue” coat color can be explained in respect to the population of the greys.
The coat color “blue,” which we perceive as dilute black (slate grey), is atypical and deviates from the official Weimaraner breed standard. In 1949, an American officer and dog breeder bought a “blue” Weimaraner in Germany and imported the dog to the US. This dog, Cäsar von Gaiberg or Tell was the progenitor of the “blue” Weimaraner population, and he was bred extensively with greys. While Cäsar had German papers and was accepted by the AKC, there has been constant discussion over his validity as a pure-bred Weimaraner. Since Cäsar, “blue” Weimaraners have been unknown to originate in European pedigrees. “Blue” Weimaraners have always been bred or imported from the American population of “blue” Weimaraners; however there are now “blue” Weimaraners being bred in Europe from American imports, although without official status. According to studbook records from the US, grey and “blue” Weimaraners have been crossed for over 60 years. Up to now, the genetic basis of the difference between grey and “blue” had not been investigated.
Inheritance of the “blue” coat
When a characteristic phenotype, such as the “blue” coat color, appears in every generation in a pedigree, and when on average it appears in at least half of the puppies, one can bet on dominant inheritance. Inheritance patterns should be evaluated on the basis of verified pedigree information. The Mendelian mode becomes obvious when heterozygous genotypes are bred. The coat color “blue” is dominantly transmitted to offspring. “Blue” dominates over grey, and the grey coat color is therefore inherited as recessive trait. This also means that when two greys are crossed, no “blue” offspring will be produced.
Analysis of known coat color genes
Like natural hair colors in humans, canine coat colors are not determined by a single gene; rather, it is the specific constellation of multiple genes which ultimately leads to the expression of a certain color. We call this type of inheritance polygenic. (Poly = many; this means many genes determine coat color together.) In order to develop a brown or black coat color in dogs, several genes have already been studied in various dog breeds. Which genes determine the coat color in “blue” Weimaraners? We studied the known candidate genes first where only small differences in respective genes are responsible for different coat colors. Such genetic differences may be present in one or more positions in the relevant gene. In order to limit financial expenditures, only small gene pieces that were already known to be involved in the expression of different coat colors were studied. Our early analyses showed that in most of the relevant genes there were no differences between typical Weimaraners from Germany and the “blue” Weimaraners. In hindsight this result is not really surprising, since “blue” Weimaraners have been interbred with the greys for more than 60 years. Therefore these dogs have to be genetically very similar.
Minute differences in the B-locus cause contrasting coat colors
Ultimately, a consistent difference between the grey and “blue” Weimaraners was identified in gene B (B-locus). The terms B and b refer to the colors black and brown. The B gene encodes the protein TYRP1 (tyrosinase related protein 1), which is in part responsible for the expression of black or brown coat color. Four regions of the TYRP1 gene were examined in great detail (see figure below).
Our analysis revealed divergent constellations in gene B comparing typically grey and “blue” Weimaraners, respectively. These varying constellations in gene B compose a so-called haplotype on a given chromosome. A single specific haplotype was detectable exclusively in the “blue” Weimaraners, and thus the cause of the “blue” coat was clear. The “blue” haplotype represents a functional TYRP1 gene, and the protein product of the TYRP1 gene enables the production of dark pigment resulting in the “blue” coat color phenotype.
In grey Weimaraners, the only haplotypes that were identified contained non-functional copies of the TYRP1 gene, thus resulting in grey coat color. Since each dog carries two inherited gene copies (one from the dam and the other from the sire), every dog has two haplotypes. For example, if two heterozygous (hetero = different; this means that the gene from each parent are different) “blue” dogs are bred, both have a functional and a non-functional copy of the TYRP1 gene. If, by chance, only non-functional copies are transmitted to a puppy, the resulting coat color is grey, and not “blue.” This represents the recessive mode of inheritance with a statistical probability of 25% for grey puppies in such a breeding constellation. Vice versa, more “blue” then grey or only “blue” offspring will arise in “blue” x “blue” breedings.
The main difference between grey and “blue” Weimaraners was identified in the B locus, but why is the coat then not simply black or brown? The observed colors are still “blue” and grey! This fact can be explained by the action of another gene product, the so-called dilute with recessively inherited d-alleles. The gene in question is MLPH (Melanophilin). If a particular change in this gene is present in homozygous state, the brown coat color is diluted to light beige, termed grey; black is diluted to slate grey, termed, “blue.” The respective change was demonstrated in all examined grey and “blue” Weimaraners in the MLPH gene associated with a dilution/lightening of coat color. Although other genes also play a role in the final coat color of Weimaraners, the relevant B alleles together with the d-alleles determine grey coat color in this breed. In contrast, a functional TYRP1 gene copy causes “blue” coat.
After the genetic difference between grey and “blue” Weimaraners was clarified, we aimed to accumulate theoretical and practical evidence for the origin of this “blue” coat color. One might suspect that a mutation in the TYRP1 gene has changed a grey into a “blue” Weimaraner; however, our studies imply that the probability for such a mutation event is extremely low. Based on the haplotypes present in the greys, at least two mutations would have been necessary to occur in order for a grey to mutate to a “blue” coat colour. The probability of such an event is less than 1: 1 trillion (1: 1 000 000 000 000). This number demonstrates that such an event is extremely unlikely. In one trillion grey Weimaraner offspring, only one “blue” puppy would occur statistically. Such an event would require several thousands of years of intensive breeding with billions of descendants. The minimal probability for such a so-called back mutation from grey to “blue” led us to apply yet another molecular genetic investigative strategy. In order to decide between the two hypotheses of back-mutation vs. crossing, old pedigrees were evaluated, and DNA of a direct-sire-line descendant of the “blue” Weimaraner forebear Cäsar von Gaiberg was prepared. The DNA analysis of this offspring could indirectly give further insight into the origin of the “blue” coat color. For this purpose, the Y sex chromosome of this male descendant was examined in greater detail.
The Y chromosomes of Weimaraners
In order to elucidate the origin of the “blue” coat color gene, the observed differences in the coat color genes are not informative. However, Y chromosomal variability can be used to trace the origin of males in male ancestral lines since the Y chromosome is always passed on from the father to male offspring. This father-to-son inheritance leads to the transfer of a specific Y chromosome over generations, and so the direct male descendant of the “blue” Weimaraner forebear Cäsar von Gaiberg should reveal the same Y chromosome as his primary forefather. Therefore, parts on the Y chromosome were examined in a direct descendant of the “blue” forefather, and were compared to the present-day German Weimaraner population. The Y chromosome of the “blue” Weimaraner forebear was significantly different when compared to the four Y haplotypes observed in German Weimaraners. One obvious explanation for this difference is cross-breeding of a black dog from a different breed into the Weimaraner population. On the other hand, “blue” Weimaraners might have existed before the official founding of the Weimaraner breed. Such dogs would not have been registered in stud books. These speculations, along with intriguing testimonies cannot be verified beyond doubt and are not documented.
Only one direct male descendant of Cäsar von Gaiberg was available for our study. Investigating additional direct male descendants would certainly offer further validated information. Such studies depend critically on the available sample material. Only one of the dogs in our study met the criteria of direct-sire-line to Cäsar.
In summary, grey and “blue” Weimaraners are genetically quite similar, because “blue” Weimaraners have been repeatedly back-crossed onto the gene pool of the greys for over 60 years. Therefore, the critical difference between both phenotypes may theoretically be reduced to a single divergent letter in the TYRP1 gene associated with the different coat color in question. On the other hand, the coat color does not directly explain the origin of a dog, because breeding of two verified “blue” Weimaraners may result in grey offspring, likely not discernible from the typically grey.
Weimaraners are grey according to the breed standard of the Weimaraner Club. Every breed club has the right to define its breed’s characteristics, including the coat color. The German standard recognizes “grey” (dilute brown) as the defining characteristic of the Weimaraner coat. The Weimaraner communities today are in a situation where an unofficial color variety of Weimaraner has developed in America. A variation that is a dilute black or slate grey, known as “blue,” is being re-introduced to Europe where they have no official status. How the Weimaraner communities choose to handle this situation of the status of the “blue” coat color is beyond the intent of our scientific study.
#Schrameyer T, Dekomien G, Pasternack SM, Reinartz BS, Santos EJ, Epplen JT. (2005) Long-and short-haired Weimaraner dogs represent two populations of one breed. Electrophoresis: 26(9):1668-72.