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Basic Genetics of Chocolate (Liver) Coloration in the Canine.
by Fred Lanting
Copyright November, 2005 -
Most black, brown, and yellow colorations are due to the presence of melanin class pigments. The word melanin is derived from the Greek word for black, and is commonly used to refer to the two or three known chemicals similar to each other, which produce the above color families. It can be said that there are only two colors in the haircoat of the canine: black and yellow, all others being variations of those. Eumelanin gives the black and dark brown colors; phaeomelanin gives the light brown and yellow ones. Certain genes on various chromosome locations affect the expression of these two so that the dark melanin may appear as black or be diluted to blue or changed to a chocolate brown, and the various shades of gelbe may exist as yellow, tan, light to darker brown, cream, etc. These genes can be referred to as modifier genes. Now, we will be talking about these modifiers as well as genes with more obvious, large-scale effects, and you should remember that whichever one is being discussed, many or perhaps most genes have different versions. The versions are always on the same location on the chromosome, and are called alleles of that gene; modifier genes are distinctly different DNA segments and have their own loci (and their own alleles).
Each gene is an individual, not duplicated anywhere else on any other chromosome or locus, but is duplicated by splitting during cell division, and may be exactly mirrored on the partner-chromosome (the condition is called homozygosity). So, we have a gene that calls for dark color parts to be black, and it appears at a specific locus. We also have a version (allele) of that gene calling for the dark color to be liver-brown and a version calling for those areas to produce blue instead. Yet there is only one “reserved director’s seat” available for the gene that determines “dark pigment” (eumelanin) and no seats anywhere else on that or any other type of chromosome. If you don’t have a ticket, you can’t sit there and direct the performance, and you aren’t allowed to sit anywhere else, either.
As the coat grows out, melanocytes manufacture melanin which then passes into the cortex of the hairs, becoming keratinized along with the cytoplasm of the hair cell as it grows up from the root through the skin. Deposited in certain patterns, these melanins along with differences in body form help a dog identify other members of his breed. That red brown tipped burnt appearance of the coat that we see sometimes, especially noticeable in black dogs, is most-often a result of sun bleaching the melanin in the hair to some extent, made more obvious by a high-protein diet, but it could also be the action of a partially otherwise hidden recessive modifier gene for dilution or lighter than-normal pigment.
If B is present (as homozygous BB or heterozygous Bb), it specifies that the “dark pigment” controlled by the gene(s) at that chromosome locus must be black. But if “bb” is there instead, they require that the dark pigment be brown instead of black (we usually call it chocolate or liver). Capital letters are used when a trait is believed to be dominant or "stronger" than the other genes that could occupy that same locus. The world allele is used to refer to a form of a specific gene. For example, B and b are two possible alleles that could exist at the B locus in the color chromosome. One calls for black pigment in the saddle, the other calls for chocolate-brown in the same place. If both members of the pair are B, the saddle (and/or other dark areas) would be black; if both were b, it would be brown or liver colored. If the cell had one of each (Bb), the dominant one (B is higher on the map than b) would prevail, and the color there would be black.
In other words, if the gene we call B is present in a GSD, eumelanin will show up as black, even when paired with b, but if B is absent and only the double b is present, that "same" melanin will be expressed as brown in the “dark pigment” portions of the coat. That is, only the saddle and other areas that normally may be black in the German Shepherd (or several other breeds) will be liver brown instead. The causative gene will have no noticeable effect on the tan parts of the dog, since another gene affects the phaeomelanin that controls these tan parts. The eumelanin affects the nose, nails, and saddle (if the dog has a “saddle-pattern” gene at the A locus). Other genes on other loci determine the extent of black or brown or blue coverage, such as the size of the saddle and markings. In many breeds, the modifiers are so numerous or so variable, that the dogs are said to come in a great variety of colors; Greyhounds and Poodles are good examples. Dogs have 39 pairs of chromosomes in a set, and you mathematicians can calculate the number of possible arrangements or combinations as being well over a billion; the odds of getting even littermates that are close to looking like twins are also extremely remote. Foxes, with 19, have less phenotype variation for this reason as well as due to the fact that breeding choices are made differently.
The Black/Brown Series, B Locus Does not Affect the Other Areas of the Coat
In the German Shepherd Dog breed, only two alleles exist for the B locus. BB or Bb will produce black pigment, but bb will affect the production of eumelanin granules in such a way (more diffuse, different shapes, etc.) that instead of black, they show brown. This brown is not the same braun as appears on the tan parts, but rather is found where black is normally found in a BB or Bb dog, such as the saddle, nose, eye-rims, etc. It is variously referred to as liver, chocolate, or seal brown, depending on the custom in whatever breed or species is being discussed. German Shepherd Dog fanciers use the term liver most of the time.
Black is dominant over liver (B is stronger than b), but most dogs I've seen that carry the liver recessive have a lot of reddish coloration in the neck and croup areas, and much mixed in the saddle as well. Most do not have black on their faces, although there is a different gene calling for a dark mask. These genes on the B locus affect only the dark (eumelanin) pigment, not the yellow (phaeomelanin) pigment. In the case of sables, the phaeomelanin's effect is seen not only on feet, belly, and tan markings, but seems to be visible in the undercoat over the entire dog. But this yellow/tan pigment is overlaid and sometimes partially hidden by the darker eumelanin in the tips of the hairs. Sometimes, whether due to the ribbing or to rows of bundles of hairs, sables may have a slightly and more or less striped or stippled appearance; however, this should not be mistaken for brindling, which is vertical in appearance.
The German Shepherd Dog with liver nose and saddle is fairly uncommon, but other than appearing lighter, the liver and tans can be as good looking as B&Ts. One very attractive liver and tan bicolor male was whelped in a litter of B&Ts. His sire was a B&T bicolor whom I wouldn't have suspected of carrying the liver gene, so this was another example of how a dog can hide his genotype. Of course, the dam had to carry the recessive, too, but as with the sire, I don't remember anything unusual about her; she appeared to be a fairly normal, though not as deeply pigmented bitch of B&T saddle marked coloration. The liver gene can appear in any coat pattern whether sable, saddle, bicolor, or even solid, as B/b is independent of the A (pattern) locus. It is fully visible in the homozygous state, bb. If the liver and tan bicolor mentioned above were to be bred to another of the same pattern and color, and if each had the ebeb alleles on the E locus, they might produce a small percentage of atatbbebeb dogs that would be solid liver. Unless intentionally bred for, this is unlikely to happen since most GSD breeders are quick to hide their “mistakes”, not realizing it is a simple Mendelian trait and easier to control than polygenic traits. Pups with disqualifying faults are harder to sell, so such dogs or their parents don't often get bred. By the way, since we have a longer string of alleles in the above example, I should state here that some geneticists like to use slash marks between loci (example: Ay/as or Ay/Ay) to make these strings of abbreviations easier to read.
I don't think I've ever seen a homozygous liver sable GSD, unless it was one of those I mistook for fawn, but the condition can happen, and would produce a less distinct contrast of overlay to the tan ground color. Much of the appearance would depend on what genes are at the C, E, A, and perhaps others unidentified loci.
There have been reports that b may be a lethal or semi lethal gene, but there is no basis in fact for this old-wives’-tale. The presence of bb has not been shown to be lethal or have any deleterious effect on viability in the German Shepherd Dog or in other breeds, either. The liver dogs I have seen are as healthy as other, “normally-¬colored” dogs are.
While to my knowledge it hasn't happened yet, a GSD could be dihybrid for both bb and dd. Have you ever seen a dog of another breed that was homozygous for both liver and blue, one whose partial genotype was bbdd? Of course you have — the ghostly silver Weimeraner is an example. Another is the “Isabella” Dobe. Yes. it could happen in the German Shepherd Dog breed, as the genes are all present in the population, and if it did occur it could be a solid color dog (atatbbddebeb), a saddle (asbbddE), a bicolor (atatbbddE), or a sable (AybbddE).
General info on The Sieger Show Experience with tour guide Fred Lanting
The SV Bundessieger-Zuchtschau (BSZS or Sieger Show) in Germany is generally held in the last week of August or first week in September at a different location each year, depending on stadiums available. (The cost of stadium for this one-weekend event, and the competition with soccer/football events that sign contracts for many per year, determine the choice.) For the past 20 years or so, I have offered my non-profit 6-7-day guided tour of the show and sightseeing, including visits to kennels and training clubs. Get an SV judge's perspective of the bloodlines and procedures, along with experienced introductions to Germany's culture and beauty. My groups come from all parts of the globe, so even just the companionship is like a world-travel experience. We usually arrive on the Wednesday or Thursday before the show, and return the following Wednesday.
Looking for a great dog-related experience combined with seeing a different part of the world? Whatever your breed or activity in dogs, the annual Lanting guided show-and-sightseeing tour could be the experience of a lifetime. Read my annual “Impressions” articles on various websites for an idea of what we've seen in recent years. Tours centered on other countries’ Sieger Shows, the BSP, and world Schutzhund trials are also available if enough people sign up.
None of "my people" have ever been sorry, and all have wished they had done it earlier! You will see the best of the breed, meet important GSD people, sometimes see another country or two, and have the over-all greatest dog show experience of your life. I also include, if you decide to join us, a variety of travel tips. I offer an SV conformation judge's perspective of the show (I also have AKC, UKC, and foreign judging experience). One year, when a travel-agency tour leader again deserted his group, they came to where my group was sitting and asked me questions. References available from previous tour participants. Testimonials are numerous. I hope you will join us and recommend this tour to your friends and acquaintances. As a judge with much experience in Schutzhund training and competition, and being very familiar with Western Europe, I am able to give the best tour possible. People going it on their own cannot see the important parts of the country (sometimes we tour adjacent countries, too), and paying for your rental car is more than chipping in to pay for the van and my expenses. Read my "Impressions" on various websites for an idea of what we've seen in recent years.
There will be 3 long days of the big show, and about 3 to 4 days of sightseeing and visits. Please let me know as soon as you can, with a $400 (US) deposit, so I can start putting my notification list together and finalize (hold) hotel reservations for you. There is a lot of work involved in putting together such a tour! I will make the hotel plans based on your deposits, & arrange the visits and van(s). Easy, fun, educational and, for most --- the unique trip of a lifetime. You will not be any younger next year, and if you don't make the decision to get out there and smell the roses NOW, while you think of it, you're more likely than not to lose the opportunity and desire. Join the group! Tell others about it, too. Fred
Contact me at Mr.GSD[at]netscape.com and tell your friends and Internet contacts.
Postal mail: 3565 Parches Cove, Union Grove, AL 35175-8422 USA
Editor’s Note: A well-respected and frequent GSD specialty and all-breed judge for many clubs around the world, with KC and other-country credentials, Mr. Lanting since 1966 has lectured on Gait-and-Structure, Canine Orthopedic Disorders, and other topics, and has judged in about 30 countries, including the prestigious FCI Asian Shows hosted by Japan Kennel Club and the KC of India, the Scottish Kennel Club, and many National Specialties in the USA and elsewhere. He has been described by a former OFA director as the world’s leading non-veterinarian authority on hip dysplasia. A dog breeder since 1945, a GSD owner since 1947, and a show judge since 1979, he has lectured at numerous veterinary schools in the USA and abroad. He is the author of “must read” books for the dog owner (see below for ordering info). Curriculum Vitae available upon request.
Announcing the new “Canine HD and Other Orthopedics Disorders” book: The expanded revision is a comprehensive (nearly 600-page), amply illustrated, annotated, monumental work that is suitable as a coffee-table book, a reference work for breeders and veterinarians, and a study adjunct for veterinary students. It is equally valuable for the owner of any breed. It covers every aspect of HD and other orthopedic, bone, or spinal disorders, and includes genetics, diagnostic methods, treatment options, and the role of environment. Your autographed copy will be mailed from the USA as soon as the appropriate amount is received and is processed. Pricing: US $68, plus $5 postage in the U.S., or ask about mail overseas. Combine orders with “The Total German Shepherd Dog” by the same author ($50 plus postage). 17 of the 20 chapters are suitable for owners of any breed.
