The article below appeared on Sat., Nov. 7, 2009 on www.colliesonline.com
| It Is What It Is! Thoughts on Joan Graber’s:
“A merle is a merle is a merle! Isn’t it? By Kathy Moll, Deep River Collies
“A rose is a rose is a rose.” (Gertrude Stein)
In the study of logic, the Law of Identity simply says that a thing is the same as itself. In our modern lexicon, “It is what it is!”
The highly regarded Collie breeder and judge, the late Joan Graber, cleverly applies the Law of Identity to the merle gene in Collies in her October 1991, article on the sable merle and Standard revision published in the CCA Bulletin. Joan was one of many Collie breeder/judges of the past who believed in the truth of two basic issues that came to the forefront 18 years ago and again today.
The two issues are paradoxical. Issue # 1 is that sable merles are as normal, healthy, and similar in quality to comparable Collies of other colors. Issue # 2 is that sable merles should be specifically included in the Collie Standard.
To illustrate that sable merles have been an important part of Collie breed development, Joan discusses the history of the merle beginning with 19th century Collie breeders in Great Britain. She bases her conclusions upon what the early creators of the modern Collie wrote and what they did based on very old pedigrees and color/ pattern descriptions that they included.
From the historical evidence, she draws some conclusions. As the earliest Collie Standards assert, color really was “immaterial” to these Collie breed developers, and they seemed to view sable merles as neither positive nor negative but simply as a fact illustrating “it is what it is.” A lack of genetic information meant that early breeders simply used the best available individuals, including “dappled sables,” in their breeding endeavors and may not have made a connection between merling as a pattern and sable coat color.
For example, the great grand dam of CH Metchley Wonder, a bitch named Bonnie Greta, is described as “dappled sable” as is Duncan, Wonder’s great-great grandsire. Since Wonder was whelped in 1886 and his son, CH Christopher, in 1887, the above mentioned sable merles were born circa 1880. CH Christopher is behind all modern Collies and, therefore, so are his sable merle ancestors.
Since merles were the most commonly seen herding dogs of the 19th century, the gene has been around for at least 150 years. Dr. Leigh Anne Clark and her team, who mapped and sequenced the merle gene in 2005, tell us that it is the same gene in all breeds. She and her fellow genetic researchers draw the conclusion that “the breeds analyzed in this study (the mapping /sequencing study) share a common ancestor,” and that “the occurrence of merle in many breeds and the fact that the first breeds to diverge from the working sheepdog population in the 1800s have merle patterning . . . suggest that the founding mutation may predate the divergence of breeds.” So, the merle gene is older than the Collie breed itself.
Joan points out that the very commonness of the merle gene may have been the reason it was “out of favor” in early Scots, Irish and English Collie show dogs. We should feel fortunate that the beauty of the merle was saved from possible oblivion by early American Collie breeders who saw the unique possibilities in the pattern.
“If you would understand anything, observe its beginning and its development.” (Aristotle)
Moving forward in the early 20th century, Chris Casselman and Thomas Halpin built the famous Hertzville Collie line based on Lodestone and Tokalon stock. Trudy Mangels explains in her Evolution of the Collie that by the 1930’s, Hertzville Collies were best known for excellent head qualities, but had also developed Collies who won Best in Show awards (6 in 1939 alone). CH Hertzville Headstone and his two sons CH Hertzville Historian and CH Hertzville Headstudy were among their best known BIS winners. Headstone was a major winner in the ring and an excellent producer. He was a sable merle. He produced 10 champions and would no doubt have had many more had he not died prematurely at age 6 years. He influenced many Collie lines and was the double great grandsire of CH Hazeljane’s Bright Future, the 4-time CCA National Specialty BOB winner.
Joan quotes such past authorities as Thompson Gray, Dr. O.P. Bennett, Charles Little, Trudy Mangels, Dot Gerth, and Bobbee Roos and mentions several Collie breeders of the late19th and early 20th centuries. Their thoughts and information are illuminating and instructive. Joan repeatedly calls upon Collie fanciers to “go study your genetics.” She explains that prejudice against the sable merle and fear of including the pattern in the Standard has often been based upon lack of genetic understanding. She likens these prejudices to those disallowing blue marked white Collies until the 1977 Standard revision because some breeders confused them with double merles. Likewise, she compares the prejudice to past hesitation to do rough to smooth breedings to improve Collie quality for fear of producing a coat hybrid.
All three prejudices are based on erroneous beliefs about genetics. Study genetics, study breed type, study Collie history. These are points that Joan makes throughout her article. Education is an ongoing process for all Collie fanciers regardless of longevity in the breed and regardless of experience!
Much has been made of “educating CCA members” about the sable merle this time around as well, and so it should. However, there appears to be disagreement about who has been sufficiently educated and what they know and do not know; what they understand and do not understand. To deny the general membership the right to a viewpoint on the grounds that they are uneducated and inexperienced flies in the face of logic and is insulting. Who has made that decision and upon what evidence is their opinion based? Attempts by some to portray CCA members who support the sable merle as uneducated beginners are gross mischaracterizations! Most proponents of the sable merle and revision are well educated, well informed and well intentioned as are most of their opponent counterparts. Make no assumptions without clear evidence!
My own observations of sable merle and Standard revision discussions over the years tells me that something of a consensus has at last been reached by most 21st century breeder/exhibitors and all but a few Collie specialist judges. With a few notable exceptions, most fanciers appear to agree (at least in theory) on Issue #1 — Sable merles are as normal, healthy and as similar in quality as comparable Collies of other colors. In fact, some who oppose Standard revision use this issue to “prove” that sable merles are covered in our current Collie Standard.
Thus, we come to Issue #2 – Sable merles should be specifically included in the Collie Standard. This, of course, involves revision to the Standard. Here fanciers definitely part company and generally fall into two camps: “They are covered as is”; or, “They are not covered as is.”
The Collie Standard must strive for clarity, must reflect scientific/genetic information as it becomes available, must provide vital information for breeders and judges toward the “ideal” in virtues, and must include guidelines for assessing faults and their degrees. Failure to apply these precepts to our Standard is a serious breech and a disservice to the Collie breed. These are the very reasons that periodic, thoughtful revision is needed to make our Standard the best it can be.
Some opponents say a sable merle revision would be a hasty move! It’s been 18 years since the last thorough discussion and poll of the members. At that time, revision was favored by a majority of the members, yet a few made the decision for the many, and no revision occurred. Sable merles have been contributors to the Collie gene pool for at least 130 years. Discussions of Standard revision to include them happen every 15 to 20 years with a majority in favor, yet no action is taken. Hasty? I think not! As Joan’s article did 18 years ago, this article also covers most of the objections to Standard revision and presents counter arguments.
Revisions should be made to clarify. If our standard was clear about the sable merle, we would not be having our current discussion. The very fact that we’re arguing proves that the Collie Standard lacks clarity on this point. Judges as of a few weekends ago continue to withhold ribbons for lack of merit because of blue in eyes. In conversations with other breeder/exhibitors, I made some discoveries. One bitch that needs a major to finish and has won under specialty judges, had ribbons withheld by a judge at a specialty because she hone blue eye. The same judge has given a specialty BOV at a very large entry to a different sable merle that also has one blue eye.
Other recent comments at shows include a judge who pulled 2 bitches for winners, and then suddenly exclaimed, “Oh, I didn’t notice that.” The “that” was some merling on one ear. The other bitch won immediately thereafter and the sable merle was not even considered for reserve. Another judge opponent of revision has given a sable merle with one blue eye and one brown Group placements at large entry shows while writing that sable merles are unacceptable in the show ring.
A well known opponent of standard revision, especially of blue in eyes, recently spoke to an exhibitor at a specialty whose sable merle had just finished. The opponent to revision complimented the exhibitor upon how beautiful the bitch was and how she deserved a specials career because of her quality. When the exhibitor expressed hesitancy because her bitch has one dark brown eye and one dark blue one, the revision opponent explained that the blue eye was not important!
More than one breeder judge has told me in personal conversation that to put up a quality sable merle with blue in its eyes means that he/she “just ignores” the part of the Standard that disallows that. Should judges have to “ignore” part of the Standard to reward the Collie that comes closest to it in his/her opinion?
Recently, a sheltie/breeder judge who had a Collie assignment explained to a couple of Collie exhibitors that a simple Standard revision to clear up the sable merle conundrum would be appreciated.
The Collie Standard says, “In blue merles, dark brown eyes are preferable, but either or both eyes may be merle or china in color without specific penalty . . . Except for blue merles they are required to be matched in color.” A simple examination of the word “required” (an absolute) illustrates that sable merles with even a small blue fleck in one eye do not have the “required” match. Therefore, judges are compelled to ignore that requisite in order to reward such a Collie for outstanding virtues. If Collie aficionados are this conflicted, imagine the confusion for all-breed judges! I truly believe that clarity IS needed. Contradictions and inconsistencies about the standard as it applies to sable merles are still common place, and the practical application of the Standard is, even now many months “post directive,” all over the place.
Joan uses the arguments presented by opponents of revision to include the sable merle and counters them. For example, one argument goes like this: “If the old breeders didn’t think sable merles should be included, who are we to do so?” Joan asserts that the “old breeders” that opponents are speaking of “are ’old’ only in that they preceded us, but they were not older than those breeders of the 1800’s to whom color really was immaterial.” The oldest breeders/developers of the Collie breed believed that color was immaterial and wrote the Standard so that it included that wording. Later revisions to the Standard changed that wording. How old is old? Is 150 years too old? How about 75 years, or 50? Would 30 to 40 years qualify one as an “old” breeder? What is too old; what is too new? “With age comes wisdom.” Well, maybe in some cases, but let’s face reality: “Age doesn’t always bring wisdom; sometimes age comes alone.” Logic dictates that wisdom and knowledge in some areas does not equal wisdom and knowledge in all areas.
However defined, there is disagreement among “old” breeders concerning sable merles and Standard revision and there always has been. So to which breeders of the past do we defer? Are current CCA mentors “old” enough? Is every “old” breeder a CCA mentor? Should fewer than half of the total mentors influence the revision decision for every CCA member? Should a 6-person review committee, all of whose members, save one, oppose revision, make the decision? Should the club president decide for 2000+ members? Furthermore, a purported AKC mandate concerning revision is mysterious indeed. AKC makes no decision for parent clubs to whom breed standards belong except in the final phase. During this last phase, exact revision wording that has been voted upon by the full membership and approved by a 2/3 majority is presented to AKC for approval. Even then, AKC is deciding to approve or disapprove wording based upon whether or not it conflicts with AKC rules. CCA owns the Collie Standard and, like other parent clubs, agrees to allow the AKC to use it.
The standard should undergo revision when genetic information and science dictate. Joan uses the blue marked white as an example. In addition to this 1977 revision, changes based on new scientific knowledge were made to the description of Collie gait. In the 1950 reworking, four colors were added to the Standard, including the blue merle. Prior to that revision, many other changes were made to reflect increasing knowledge. Why is this case different? It isn’t!
Articles published in scientific journals in recent years have added new information to our understanding of the merle gene. Why would we close our eyes to this new educational opportunity? Why not apply what we know now? Our Standard attempts to describe the ideal. This does not mean that the attempt at such description in itself equals perfection. The Collie Standard is better than most breed standards and is a tribute to the work of many individual fanciers over the past 100+ years. It has undergone quite a few rewrites and revisions throughout Collie history. Its authors have said nothing, to my knowledge, to indicate that they believed their writing was “perfect.” We are striving for perfection in our breeding programs in actual living, breathing Collies. There is no evidence that breeder’s of the past wanted future breeders to treat the Collie Standard as though it were “written in stone” when clarity and science dictate otherwise. While describing desired virtues, the document also assesses faults and the degree to which they should be penalized.
“We can’t encourage blue eyes in sables,” is the most vehement argument against sable merle inclusion, and Joan addresses it. She does so with the genetic information available to fanciers in 1991. Most of that information is on the money. However, we know even more in 2009 about the merle gene than we did in 1991. For instance, we now know that the merle gene is an insertion gene that randomly copies itself and that the length of its “A” tail is also random and accounts for wide variation in merle patterning. We also know that this same randomness applies to eye color in all merles. Those with the insertion gene present as merles, but the gene’s “A” tail length controls the degree of merling as well as the randomness of eye color. Both blue merles (homozygous, for black and tan) and sable merles (homozygous for sable, as well as heterozygous for sable) have random chances for pigmentation in the eyes.
The same mutation insertion and incomplete dominant mechanisms that randomly put merling on these Collies also produce the following possibilities on eye color: both eyes brown; both eyes blue; one eye of each color; partial blue and brown in one or both eyes; and blue flecks in brown eyes. So while eye size, shape and set are genetically controllable through selective breeding, the presence of blue or merling in the eyes of merles is not. Breeders do not have the option to “breed for blue eyes,” even if they ignore the Standard’s preference for dark brown! A sable merle with two blue eyes is no more likely to reproduce them than is a sable merle with two brown ones, according to the best available genetic studies. Either will produce randomly occurring brown, blue and merling in eyes in offspring just as blue merles do. If such were not the case, we would have seen an ongoing increase in blue eyes in blue merles. No such thing has happened! “A merle is a merle….” and “it is what it is.”
While dark brown eyes would be the preference of breeders and fanciers in both blue and sable merles, blue in eyes may or may not detract appreciably from the merle’s expression and is an individual matter of proper evaluation. The Collie Club of America Standard Review Committee’s own report uses quotations from breeder/judges concerning specific sable merles shown to them. One of the common themes that emerges is beautiful expression. Many of the sable merles to whom they attribute sweet expression have blue or merling in eyes and even total blue. All well educated Collie folk know that color is only one of many contributors to expression. Joan says, “Not only the color but also the size, shape, placement, large or small haw, light or dark haw, affect expression. In all cases we are dealing with our definition of expression, and we need to remember expression is an aesthetic rather than a functional attribute.” She goes on to quote Bobbee Roos on the subject of coat color: “True Collie expression is inevitable regardless of color because of the head properties.”
Blue merles were included in the 1950 rewrite of the Standard. Over the past 59 years, their inclusion with merle or blue eyes allowed, but dark brown preferred has contributed to the breed, not harmed it. Merles exist, fanciers use them in breeding programs, many exhibitors show them, none of that will change. As for judges, a West Coast friend recently made this point, “If the judge feels that the blue eyes affect the expression of the dog, the judge will place the dog accordingly. The exhibitor will face the same considerations in deciding whether or not to show the dog. I suspect that by changing the Standard, we won’t see either an increase in blue eyes or a significant change in the number of blue eyed sable merles put up.” I agree with my friend! “A merle is a merle…” Revision is made to clarify and to reflect new scientific knowledge!
Another argument, “We open up the Standard to other changes, some of which might be bizarre,” is specious. Only a few opponents of revision have brought it up to my knowledge. Proponents have stayed on point. This revision is ONLY about a long over due, decades-old request for revision to include the sable merle. That was all that the membership meeting vote addressed and is all that 71% of all CCA members cast their votes for or against.
Misunderstanding abounds about what is involved in revision. Our own constitution calls for a process; even though, in my opinion, it hasn’t been properly followed so far. With the assumption of power comes responsibility. For any elected official there is always a mandate to follow our constitution, be honest with the membership and make its wishes a prime consideration!
“So what’s the turmoil?” Joan asks. Those who have suggested possible revision language have done so in ways that are unobtrusive but clear. The sought after revision described by many proponents requires but a few words and affects less than 1% of the Standard’s language to clarify and reflect current knowledge!
Joan tells us, “Those who say we should not be accommodating the Standard to what we are breeding, or that our present Standard was outlined by our founding fathers, need to review all the Standard changes since the mid 1800’s . . . I would like to think that we make changes in the Standard to clarify certain areas for breeders and judges as well as to correct errors as we gain more knowledge, especially in areas of genetics and inheritance.” Since we’ve been breeding sable merles continually since the 19th century development of the breed, we’re hardly accommodating the Standard to a fad! As Joan also reminds us, “The sable merle is not going to go away.” And I would add, “Why would we want it to?”
Related article> A merle is a merle is a merle! Isn’t it? by Joan Graber, Rudh’Re Collies
The article below appeared on Sat., May 16, 2009 on www.colliesonline
“The Coat of Many Colors”
“Life is a celebration of passionate colors.” (L. Cator)
Much is being discussed of late – actually for the past few decades – about sable merle collies, the breed standard, and color/pattern genetics. Thanks to the “leaps & bounds” growth of DNA research and the work of a few dedicated veterinary geneticists, we have far more solid science available than ever before to teach us about color and pattern in our wonderful breed.
This article is about the dedicated work of Dr. Leigh Anne Clark and her colleagues at Texas A&M and that of Dr. Phil Sponenberg of Virginia Tech and his colleagues. Their studies and research with various dog breeds have brought color/pattern genetics into focus and answered important questions for breeders.
In 1984, Dr. Sponenberg published a study in The Journal of Heredity involving 66 puppies from a double merle Australian Shepherd from which he concluded that the merle gene was due to a mutation by what is called “transposable DNA .”
In 2005 Dr. Clark and her colleagues successfully mapped the merle gene in all breeds, sequenced the merle gene of Shetland Sheepdogs, and published their findings in The Proceedings of the National Academy of Sciences, in January 2006, under the catchy title, Retrotransposon insertion in SILV is responsible for merle patterning of the domestic dog. Dr. Clark’s research was based on Dr. Sponenberg’s earlier work with Aussies. I am the conduit for their expertise and that of my good friend, molecular biologist Dr. Mike Vaughan. Mike is a fellow collie fancier and CCA member who helped me “translate” the science so that I could relay it accurately to you.
The two base colors in collies are sable and black & tan. Most of us know, that in collies, sable is dominant and tri-color recessive. A puppy inherits one color allele from each parent. An allele is an alternate form of a gene. Therefore, if a collie inherits a dominant sable allele from each parent, he/she is a “pure for sable” (homozygous for sable). On the other hand, if a recessive black & tan color allele is contributed by each parent, the collie will be a tri-color (homozygous for black & tan). Some collies inherit a sable allele from one parent and a black & tan one from the other making them “tri-factored” sables (heterozygous genetically although still sable in appearance).
Dr. Mike explains the process:
Specialized skin cells in Collies produce pigments called melanins; these pigments come in black or tan. These are not free dyes, dissolved in the cell water but instead are solid pigment particles built up in tiny bodies made of proteins called melanosomes. The skin pigment cells pass these melanosomes into hair follicle cells which produce the hair strand. If a hair follicle does not receive pigmented melanosomes, the hair strand it forms is white, as in the majority coat of a white Collie or the neck region of colored collies (from the Irish pattern gene). If all the melanosomes that a growing hair strand receives contain black melanin, the hair strand itself will be black, as in the black areas of a tri-color Collie. And if the melanosomes the follicle receives from the pigment cells are all tan, the hair strand will be sable, as in the coat of a pure sable or tan points on a tri-color.
All cells of a Collie have the same basic genes, but no single cell expresses all those genes; instead, in each cell, some genes control the expression of others, turning some on and some off. This complex and miraculous control process not only produces beautiful puppies; it continues throughout the life of the dog.
An example is the mahogany sable coat of tri-factored sables. At birth these puppies are usually dark tan. But as older puppies, many look much like pure sables, and almost all the developing hair in the first coat is sable. However, as the tri-factored collie ages, some black melanosomes are put into the growing hair strands, so the coat develops a deepening dark appearance.
Sable Merle & Blue Merle Genetics – Separating Fact from Fiction:
Dr. Mike tells us, “The merle allele is not a color allele; in fact, it produces no pigment at all.” A misconception that is apparently still alive and well is that sable merles are a mysterious mishmash of colors in conflict. This is fiction. A sable merle is not a combination of sable, tri and blue. Here’s why. There is no color gene in collies for blue coat color, only sable and black.
The merle allele “dilutes” color on the body. In genetically black dogs, it turns the black coat grey but allows some melanosomes to be fully loaded with black pigment so that black color comes through completely on some parts of the coat. The merle gene has the same affect on a genetically sable collie, turning most such collies a lighter sable.
Of course, when a collie has one sable color allele and one black & tan color allele, it is still a sable, just a darker one. This phenomenon is called incomplete dominance (an interaction between alleles/genes). Incomplete dominance means that the black and tan recessive allele in a tri-factored sable is only partially suppressed by the dominant sable color allele. The sable phenotype (appearance) is expressed, so it is dominant (or, more accurately, incompletely dominant) while the suppressed black & tan allele is incompletely recessive because it does darken the sable by adding in more black. The resulting collie is, of course, still a sable. So when a merle allele with no pigment acts upon the coat, various shades of sable come through.
Sable merles, whether pure for sable or tri-factored sable, are still sable collies; one is simply a darker sable than the other. There is no conflict among the genes; only a normal, expected and predictable interaction!
Collie Merle Pattern:
Again, keep in mind as you continue to read that the merle allele is NOT a color allele. I know we’ve said this before, but it’s worth repeating!
We’ll need a few definitions to understand how merle works. For example, we briefly mentioned the meaning of allele earlier. Here’s an expanded definition: An allele is one of two or more alternative forms of a gene at the same site on a chromosome that determine alternative characteristics in inheritance.
SILV, a term in the title of Dr. Clark’s paper excerpted later in this article, is a gene that is important in pigmentation because it produces a protein that forms the matrix (background) on which melanin is deposited. When SILV is used to refer to a gene, it is italicized in scientific writing. When SILV refers to proteins in such writing it is not italicized. I have tried to adhere to that practice in this article.
Transposable DNA, also called SINE or retrotransposon, is another term we need. These three terms are interchangeable. These refer to sections of DNA able to copy themselves and inset themselves at random into other areas of DNA. All merles have a SINE inserted in the SILV gene. A SINE is organized into 3 parts: a head, a body and a tail. The tail is a fragile string of “A” nucleotides. Nucleotides are chemical letters in the DNA code. The “A” tail may shorten or lengthen each time it is copied.
The length of the “A” tail controls the degree of merling seen in a collie. A collie with little or no “A” will present as a cryptic. A cryptic is a merle who is not physically distinguishable as such or who mainly looks tri-color or sable with only small areas of merling. Collies with longer “A” tails in SINE present as merles, but the tail length controlsthe degree of merling and is responsible for the random degree of mottling as well as the randomness of eye color.
Dr. Clark summarizes the merle allele’s affects this way: Merle is a coat pattern caused by a dominant mutation in a pigmentation
gene called SILV. The mutation (an insertion of repetitive, mobile DNA) causes dilution of the base fur color and often blue eye color. Merle affects all coat colors, but is more apparent in dogs with darker-colored coats (e.g., black) than those with lighter-colored coats (e.g., sable). Coat color is determined by other genes. Because of the type of mutation that causes merle, merling is random and characteristics such as the size and number of colored patches and eye color cannot be predicted.
So how does the mobile, inserted “transposable DNA” (remember that synonyms are SINE & retrotransposon) in merle interfere with the production of SILV protein needed to form pigmented melanosomes? Dr. Mike explains with an analogy that the insertion works on pigment in the following way: “It is as if a nonsense string of letters is inserted at random into a meaningful sentence, making it impossible for us to read it.”
A blue merle is a tri-color (homozygous black & tan) with the merle allele of the SILV gene. A sable merle is a sable that can be either homozygous sable or heterozygous sable with the addition of a non-color producing merle allele. Merle actually has the affect of preventing some of the color from fully appearing on the collie.
Dr. Mike explains further:
With the addition of merle, things get interesting! The “transposable DNA” inserted into the merle gene contains a long string of “A’s” that “turn off” the SILV gene so that it cannot produce the SILV protein helping to form melanosomes. It turns out that mutations occur in this string of “A’s”quite often as cells divide, decreasing the string’s length. The result is that the body of a tri-color (with merle) develops, first as an embryo and later after birth, with clones of skin cells with new mutations in the “A” string. The shortened “A” prevents the “transposable DNA” from inactivating the SILV gene, allowing normal melanosomes to be made again. In other words, now there are two mutations present, with one reversing the other. So this clone of skin cells, with normal melanosomes loaded with black pigment, will produce a spot of hair that is black or dark grey. This spot on the puppy now has two mutations, one reversing the other. Since there are a lot of these spots, some dark gray and some quite black, scattered randomly over the dog’s body, the puppy ends up with the classic “blue merle” appearance.
This is amazing! When you next look at a blue merle Collie, look at the spots of black and grey on its body, giving it its beautiful coat and think that you are literally looking at mutations, creating each unique spot. The SINE gene is still there in the SILV in those spots; it has just been inactivated in them, by the second mutation decreasing the length of the string of “A’s.” One mutation is canceling the effect of another. You always knew Collies were clever!
I should add that the merle mutation also often affects the eye color of dogs inheriting it; the effect is to produce one eye or both eyes that are completely or partially blue. This does not always happen; some merle dogs have two dark eyes, though close examination may show a fleck of blue coloration.
Merle Gene Mapping:
The 2005 mapping of the merle gene using 50 Shetland Sheepdogs not only tells us what genetic mechanisms produce merle genetics but also that merle is the same in all breeds.
Dr. Clark and her colleagues explain the merle gene mapping phase of their work in Retrotransposon insertion in SILV is responsible for merle patterning of the domestic dog as follows:
(We) carried out a whole-genome scan using the Shetland Sheepdog and were able to map the merle locus… To determine whether the SILV mutation causing merle patterning in the Shetland Sheepdog population was breed specific, merle and nonmerle dogs representing six other breeds (Collie, Border Collie, Australian Shepherd, Cardigan Welsh Corgi, Dachshund, and Great Dane) were analyzed for the insertion. Merle dogs from all six breeds were heterozygous and one double merle Great Dane was homozygous for the insertion.
Merle Gene Influence on Eye Color AND Its Influence on Ear & Eye Abnormalities in Double Merles:
Both blue merles (homozygous, for black & tan) and sable merles (homozygous for sable, as well as heterozygous for sable) have random chances for pigmentation in the eyes. The same genetic information mechanism involving mutations in the length of the “A” tail in the SINE that randomly puts merling spots on these collies also produces the following possibilities on eye color: both eyes brown; both eyes blue; one eye of each color; partial blue & brown in one or both eyes; and blue flecks in brown eyes. So while eye size, shape and set are genetically controllable through selective breeding, the presence of blue in the eyes of merles is not. While dark brown eyes would be the preference of most breeders & fanciers in both blue and sable merles, blue in eyes may or may not detract appreciably from the merle’s expression and is an individual matter of proper evaluation.
Below is the explanation for the relationship between pigmentation and its effect on normal eye and ear development from the Clark et al. paper Retrotransposon insertion in SILV is responsible for merle patterning of the domestic dog (bold below is mine):
Melanocytes are pigment-producing cells present in many tissues, including the epidermis, hair follicle, inner ear, and choroid of the eye (33). Melanocyte cell populations differentiate from unpigmented melanoblasts released from the neural crest during embryogenesis (33). The complex process in which melanoblasts migrate and differentiate into melanocytes is not fully understood; however, the study of pigmentary anomalies may accelerate identification of genes important for normal development.
This research and prior work done by Dr. Sponenberg tells us that normal inner ear and eye development is, in part, controlled by presence of pigmentation. One copy of the merle gene causes no harm in the collie; however, two copies are a different matter. Fanciers and breeders call homozygous merle collies, those that receive a merle allele from each parent, by a variety of names, all of which describe the same collie: double merle, double dilution and white merle. These collies may have varying degrees of vision and auditory abnormalities.
As Dr. Mike says, “Despite these defects, double merles may live normal lives. In fact, some are of superior conformation and when mated to non-merles have produced splendid Collies that are perfectly normal blue merles or sable merles, successful in the show ring and at performance events.”
Again, the predisposition for abnormalities in double merles varies widely with some having both usable vision and hearing, some having one or the other, and some having neither. However, when a homozygous (two copies) merle is bred to a non-merle collie, the resulting offspring receive color/pigmentation from both parents but the merle allele from only the homozygous merle parent. All resulting puppies develop into blue merles or sable merles depending upon the base colors of each parent. These offspring will NOT have or produce any eye or ear abnormalities related to pigmentation since they only have one merle allele from the double merle parent and none from the non-merle parent. Their own merle offspring will also be normal.
Genetic Testing for the Merle Gene:
A genetic test for the merle gene will be available again soon and can give complete confidence that a dog is or is not carrying the gene. Nothing more than a simple cheek swab is needed from your collie – a non-invasive test. For more information, go to: http://www.idexx.com/animalhealth/laboratory/realpcr/index.jsp
Normally, we know whether or not our collies are blue merles or sable merles. However, there are some questionable situations that may arise. Cryptic merles are an example of a collie that may need genetic testing.
In phenotype (appearance) some collies can appear to be tri-colors or sables without merle. However, these individuals may produce as merles because this is their genotype. If that happens, then a genetic test is in order. Furthermore, if there is any doubt at all as to whether a collie you own and plan to breed has a merle genotype, then testing prior to breeding is needed. Because of the probability of producing 25% double merles, merle to merle breedings would only be appropriate in very specific situations.
We’ve come full circle in our discussion of the collies’ beautiful colors and patterns. Genetics is an amazing and wondrous science with a great deal to teach us as breeders and fanciers. If we take the time to educate ourselves properly and make an effort to keep up with the latest that science has to offer, our beloved collies will be all the better for our knowledge.
Excellent quality sable merles, like excellent quality blue merles, sables, tri-colors and color-marked whites, have a great deal to contribute to the collie gene pool. Fear and misinformation should not stand in the way of what they have to teach us! As Dr. Mike explains, “There is absolutely no fundamental distinction between blue merle collies and sable merle collies other than the fact that blues, having inherited black & tan alleles, have diluted grey bodies with grey and black spots while sable merles have similar spots on sable bodies. The fact that a Collie is a merle, blue or sable, is simply an important characteristic to be noted, not one to be used to stigmatize it.”
“Continuity gives us roots; change gives us branches, letting us stretch and grow and reach new heights.” (P. Kezer)
Author: Kathy V. Moll – Deep River Collies – My deepest appreciation for allowing me to interpret their research and for their technical assistance & editing to Dr. Leigh Anne Clark, Dr. Phil Sponenberg, & Dr. Mike Vaughan!
Dr. Leigh Anne Clark TX A & M University
Retrotransposon insertion in SILV is responsible for merle patterning of the domestic dog, by Leigh Anne Clark et al. was published in the National Academy of Sciences PNAS
Other interesting articles about sable merles may be found here: