This double merle dog was born deaf and blind without recognizable eyes (anophthalmia). Other double merles can appear normal or so severely disabled as to not survive gestation.
We learned before that recessives are dangerous because when they are doubled up it often means that a vital bodily process is entirely broken leading to disease. Recessive disease is more common than broken dominant disease because there’s no hiding from dominant alleles, they show up if you have one copy. Thus, they are more likely to kill before reproduction and they are easier to weed out with selective breeding techniques. It’s also easier to break an existing function than to have a mutation create a new product that is actively disruptive or lethal (entropy).
But as with most things in biology, all alleles don’t fall into an easy binary classification as dominant or recessive. Another option is semi-dominant (also called incomplete dominant) where having one copy of a gene leads to a change in phenotype, but not as severe as the effect seen in a homozygous individual. For example, long coat length in German Shepherds is a semi-dominant allele. Two copies of the short coat gene leads to 2 inch hair, one copy of the long coat results in 3 inch hair, and two copies of the long coat allele result in 6 inch hair.
Some semi-dominant traits are harmful with a single copy and lethal (or profoundly debilitating) with a double dose. In this respect they are worse than recessive disease because the single-copy state is actively selected for, creating a slew of carriers, and unlike recessives the single copy situation can still lead to defects. Unfortunately, the lethality of these genes is often pre-natal so we don’t have to actively confront the disease and the morality of breeding for these traits. Out of sight, out of mind.
Three popular traits which we see in purebred dogs that are lethal semi-dominant are the merle gene, the bobtail gene, and the most prevalent hairless gene.
Double Merle, Single Merle, No Merle in the Aussie
Merle – Also known as “dapple” in Dachshunds and half of the equation (with the Harlequin gene that modifies the expression of the Merle gene; the Harlequin gene is also embryonic lethal in its homozygous form) in Harlequin Great Danes, the Merle gene is present in numerous dog breeds: Alaphaha Blue Blood Bulldogs, American Cocker Spaniels, American Pit Bull Terriers, American Staffordshire Terriers, Australian Shepherds, Beaucerons, Border Collies, Cardigan Welsh Corgis, Catahoula Leopard Dogs, Chihuahuas, Collies, Dachshunds, Great Danes, Koolies, Hungarian Mundis, Miniature Pinschers, Norwegian Hounds, Old English Sheepdogs, Pomeranians, Poodles, Pyrenean Shepherds, Shetland Sheepdogs, and is emerging in breeds like the Rat Terrier by way of down-low out-crosses.
The [semi-]dominant allele M acts on uniform pigmentation to produces an alternating pattern of dark versus light that is also known as dapple. The recessive allele produces uniform pigmentation when the dog is homozygous (mm). Heterozygous merle (mM) in an otherwise black dog produces a blue merle, and in an otherwise brown dog produces a red merle. Dogs homozygous for the dominant allele (MM) can be mildly affected to the naked eye or severely affected, depending on breed and even varying within a breed. Severely affected MM individuals are often nearly all white, deaf, sterile, and blind or affected by various visual abnormalities.
Because Merle has a varied penetrance, due to the fact that it disables color production to different degrees and only in some cells, the associated disease paths (mostly in the audio/visual area) are also variable, but much more prevalent in the homozygous state than with only one copy:
Reetz et al. reported hearing results for 38 dachshunds (Tekels in German): 11 double merles, 19 single merles, and 8 non-merles. They found hearing loss – slight to total, unilateral or bilateral – in 54.6% of double merles, in 36.8% of single merles, and in none of the non-merle.
…
In an unpublished study performed by myself and these investigators at Texas A&M University,7 70 merle dogs from five breeds (Shetland sheepdog, Australian shepherd, collie, Great Dane, and Catahoula leopard dog) had BAER hearing tests performed and merle genotype determined by DNA tests. Of 22 double merles, 8 were bilaterally deaf (36%) and 2 were unilaterally deaf (9%). Of 48 single merles only one was unilaterally deaf (2%), a Great Dane that also carried the piebald gene
It is believed that Merle leads to disease because the same mechanism that destroys or limits a cell’s ability to produce pigment that we interpret as coat color patterns also destroys a secondary function of those compounds which regulate blood supply in the tissue surrounding the sound sensing follicles within the ear.
The deafness, which usually develops in the first few weeks after birth while the ear canal is still closed, usually results from the degeneration of part of the blood supply to the cochlea (the stria vascularis). The nerve cells of the cochlea subsequently die and permanent deafness results. The…vascular degeneration…appears to be associated with the absence of pigment producing cells (melanocytes) in the blood vessels. All of the function of these cells are not known, but one role is to maintain high potassium concentrations in the fluid (endolymph) surrounding the hair cells of the cochlea; these pigment cells are critical for survival of the stria.
Iris Hypoplasia (2:00-5:00) in a homozygous Merle Aussie with a small Coloboma (1:00).
Homozygous merle (double dapple) is also associated with various disorders of the eye. Iris hypoplasia (aniridia) is a disease where segments of the iris are missing or deficient; because the iris is unable to adjust the amount of light that enters the eye, this disorder causes photophobia which is the inability to see or extreme discomfort in bright light situations. Similar and more severe is a coloboma where part of the iris, retina, and/or optic nerve is missing.
Another related condition is called Congenital Corectopia or ” eccentric pupils” where the pupil is not centered in one or both eyes. In humans this is associated with chromosomal and central nervous system abnormalities.
At the extreme, the eye might be abnormally small and defunct (microophthalmia) or entirely missing (anophthalmia).
Since Merle is both common and desirable and appreciation for the gene’s deleterious nature is often trumped by denialism or ignorance, the double merle is one of the more compelling cases of aesthetics vs. health in dog breeding.
A blind and deaf double merle sheltie with very small eyes.
Some Shetland Sheepdog breeders in an attempt to create an all-merle line (if not a separate breed entirely) that always produced 100% merle puppies (to “breed true”) bred from several double merle sires that were apparently asymptomatic for merle related diseases.
A double merle parent is required to consistently produce an all-merle litter, preferably with a non-merle mate such that the entire litter would be the most desired homozyous merle. But obviously such a breed is doomed to failure as the required breeding stock is the undesirable double merle x the undesirable non-merle.
Attempts to create a sustainable all-double-merle gene pool failed given that the asymptomatic quality of the initial double merle sires was not realized in the offspring and the highly bleached out coat was not as aesthetically pleasing to the fancy as the heterozygous merle.
The same is true of the Miniature Pinscher. When Merle was banned from the breed standard in the German Kennel Club, some breeders refused to give up on the allele and tried to start their own all-merle breed. It didn’t end well.
That’s a unique quality to lethal semi-dominants: you can never breed true. This is why you’ll never see an all merle breed, a breed that has all natural bobtails, or an all hairless Xolo/Peruvian Inca Orchid/Chinese Crested. For this to happen you need 100% saturation of the allele, dominant or recessive, and since the lethal semi-dominants are undesirable or never reach term, this state can never be reached (although some idiot breeders have tried).
In upcoming posts I’ll discuss two other prevalent lethal semi-dominant traits in dogs: bobtails and hairlessness.
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All of the lethals you have mentioned here are either dominant or semidominant.
Which is really interesting.
retrieverman recently posted..Merle as a lethal semidominant
I think they’re all semi-dominant because the single copy form might be deleterious but it’s not nearly as pronounced as the homozygous form. Unlike Merle which leaves enough of the doubles alive, I’m not aware of any of the bobtail doubles making it. That’s why some authors might mistake it for simple dominant, they never knew they were silently killing all the doubles, so it LOOKS like a dominant.
This is what confused many early breeders of the Xolo/Crested, when they tried to get rid of the coated members of the breed (and some Xolo people still think they can do it, to this day). Nobody figured it was anything other than a simple dominant for many years. They eventually caught on sometime in the 1970s.
Not sure what people thought the coated pups were before then, since there’s no mention of them in any accounts of hairless dogs as far back as I can find (1866 at the earliest) — I suppose people assumed they were just mutts with a different sire when they were born and quietly disposed of them.
It would be interesting to figure out how long ago the Merle gene arose. It’s fairly widespread among a number of fairly diverse breeds and may have existed in others (the Altdeucher has a merle version, called the “tiger” and a description of an early Belgian herding trial indicates merle may have existed in Belgian herding dogs when they were still a “landrace”). It exists in Beaucerons but not Briards, so I would guess that in some breeds, it may have existed and has been eliminated. People like the unusual color patterns, and so it is selected for, regardless of the health issues. There’s several animals where a color pattern (spotting & “paint” colors in horses for example) seems to be associated with negatives yet the color is very ancient. I’ve always wondered what gene it is that “painted dogs” have — they aren’t the same species as dogs, but they are at least distantly related and their color patterns are as varied as merle ever was. I’d be willing to bet that some person some day will try to bring that gene into dogs if it isn’t the same gene .Peggy Richter
I had no idea that a single merle gene could have such disastrous consequences. I had believed that the merle gene is only dangerous when it is doubled up. I appreciate learning this very much.
Lochinbrae BCs recently posted..This will be the father of our litters who will be born April They will not be ready to leave home until June
I don’t want to overstate the case. The PhD’s paper I linked to says that he thinks that the dangers are overstated based on the first study that was published. He also points out that in his own work he found that dogs with a single copy were not 100% deaf despite having deafness over a wide range of tones. The only completely deaf dogs were double merles. I don’t know how much comfort this is though.
I appreciate the need not to exaggerate. I don’t want to tell merle border collie breeders that a lot of their puppies will be deaf when in fact they will only be lack a range of hearing. I try not to discredit myself too much. But lacking a range of hearing is all the reason I need to stay away from the gene.
Lochinbrae BCs recently posted..This will be the father of our litters who will be born April They will not be ready to leave home until June
The missing range of hearing is highly problematic for a trial dog given that (1) Whistles are the signal of choice to work a dog at distance. (2) These signals are high in pitch. (3) High pitch hearing is the most delicate.
While I have not read if this has been confirmed with the Merle gene, I know that in humans that as we lose hearing it’s almost always from the highest range first. Those hairs are the most delicate to resonate with the high pitch sounds, and since the science says that the Merle gene starves the hairs of blood supply, I’d make an educated guess that it’s easier to starve a fine hair than a thick one.
we took in a stray catahoula pup when i was young who appeared to be double merle. he was mostly white with the gray dapples here and there, and he was totally deaf. he was a wonderful dog though and i still miss him dearly. : ( although his eyesight seemed to be fine : )
The refusal to acknowledge the Double Merles among some breeders is disturbing.
Dave recently posted..Basal Breed
There’s a couple of articles on merle issues in the Aussie (and I expect that the same things occur in other merle dogs) –
http://www.ashgi.org/articles/eyes_can_you_see.htm
Can You See?: Inherited Eye Disease in Aussies
First printed in Double Helix Network News, Spring 1998, Rev. Jan 2010
by C.A. Sharp –which points out eye problems. You’ll see in the text where the incidence of many problems is far higher in merles than in other colors
and http://www.ashgi.org/articles/color_troub_merle.htm
The Trouble With Merle
First published in Double Helix Network News, Vol. IV No. 2, Spring 1996
by C.A. Sharp
–there are others as well.
Peggy Richter
Merle does not exist in the American Pit Bull Terrier or the Amstaff. Any merle “pit bulls” are most likely Catahoula crosses.
I am very disturbed by the numbers of people who think that breeding double merles is ok ever. I just don’t understand it. How can color EVER be that important? (Sometimes I hear the argument that the “only” dog who could possibly ever be a good match for my merle bitch just happens to be merle also, so oh well, I guess we’ll just have to breed merle merle because there’s no other choice! I call BS.)
My BC is merle. He’s pretty, sure. And he’s a good dog. And I’d be just as happy with him if he were black and white.
Katie recently posted..Photobomber strikes again
I doubt the pitbull breeds got it from the curs. While plausible, one have to remember merle isn’t a recent mutation and has been showing in old breeds for a long time. Cocker spaniels also carry the merle genes, but the colouration isn’t recognized by any kennel clubs. The same is said for the Miniature Pinscher which did used to have merle as part of their ancestry before the harlequin colouration was dropped from the standards.
Failure to meet the standards of conformity does not means the dogs were crossed. One have to remember, working dogs are seldom talked about, it’s the dogs who are idolized that get the attention. Face it, we now live in a world where we think we must conform to the standards set forward by trial and show people– of COURSE “merle” isn’t part of the terrier! They are not formally RECOGNIZED.
Dave recently posted..Basal Breed
I’m not sure about individual registry policies for Pibbles and kin, but there is at least one (perhaps rogue) registry that seems to be celebrating this coat pattern in the breed.
http://pitbullregistry.com/merle%20pitbull%20pictures.htm
Like the Border Collie, I suspect that the pit bull (landrace) is easily a top 10, if not top 5 popular dog despite never making the list of such given that the AKC does not own the majority of the breed pool for either.
I’d be curious to know what percent of the breed is being bred under the different standards of the various registries, plus unpapered dogs of any admixture.
That’s actually one of the Pitbull landrace’s strengths, they are in many ways still a landrace with recent mixture with other breeds. Broad diversity of genes, alleles, MHC health possibly, etc.
And yes, Steve is a very handsome dog. Especially his ears.
http://www.apbtconformation.com/merle.htm
For those who accept that the APBT is a purebred (as much as an breed is a purebred) and that the only legitimate registry is the UKC (or the AKC for the AmStaff), merle is NOT and never has been a component color. Dogs of this color are NOT APBTs anymore than the “american bully” mutants are.
The other old registry for the APBT, the ADBA, actually was accepting merles. They recently disavowed the color, but not on the grounds of it being illegitimate in the breed, but because of “health” issues associated with the color
http://adbadog.com/p_pdetails.asp?fspid=73&pg=73
Actually the UKC standard used to accept any color. Go back and look at the old standards. Also I had an ADBA registered merle female with an extensive ped. that went clear back to some of the foundation bloodlines in this country.I also believe that if merles are not accepted than why are Tri-colored dogs which started showing up only about twenty years ago. Just seems like more breeder club politics to me.
The UKC may have accepted “any” color, until they realized that people were claiming merle APBTs as purebreds, which is a genetic impossibility. As for the ADBA ,they have been known for moneygrubbing and paperhanging for decades (they “register” tens of thousands of “APBTs” each year and it’s THOSE dogs that are the ones, most likely, who get in trouble). They now accept any “breed” for registration merely with some registrant paperwork. The primary interest of the ADBA IRT the APBT has always been in the “working” (wink wink) function of the breed. For those who care about “work”, purity of breed is irrelevant. If a merle “APBT” can “work”, that’s all that they care about. And indeed, if all you care about is the work, nothing else matters. They didn’t promote health testing either, because “if the dog can “work”, it must be healthy”.
Now, if you DO care about “breed” at all, then you need to care about how to maintain such a thing (artificial as it is) and keep the dogs healthy as well.
Unlike merle, tricoloreds (and blue for that matter) have been known in the history of the APBT and its forerunner the SBT since the beginning, probably from Manchester terrier input. SBT advocates tell me that tri is in disfavor because if allowed, it would overwhelm the other colors and you’d end up with mostly tri SBTs.
They’re are paintings of dogs that look like APBT’s as far back as the 1400’s. There is also no absolute proof that the SBT’s is a forerunner of the APBT. All of the early British Isle dogs were originally bred for bull baiting and boar hunting and it seems logical that the larger blood line dogs were still around when baiting became illegal in 1835 and the smaller SBT’s which were being used in the pit started showing up. As for the genetics, I believe your mistaken, many Mastiff breeds have a merle pattern in there background. I would really like see your genetic proof of why an APBT can’t be a purebred. The UKC accepted them for more than 100 years before disqualification, not because of purity but because health concerns. You should study your breed history a little closer. The reason I say this, is that up untill about 80-100 yrs.ago there was no breed called a Catahoula it didn’t exist. When people in the south started breeding for this type of dog a lot of there foundation stock consisted of APBT’s because the breed was already a proven boar dog. I am fairly confident that merle coloration came from the APBT’s they used. Also I would like you to suggest what other dog was used if it wasn’t the APBT. You have to remember that both the UKC and the ADBA these dogs in the bloodlines for more than 100 years.
I’ve always found it curious how double dilutes vary on if and how much they are deaf or blind.
I read one paper a while ago that suggested one factor, that might affect level of disability, is how much white the dog has. Not the white caused by the merle gene but whether the dog is a Minimal White (S), Irish White (si) or Extreme White (sw). That is, a double dilute dog that has no white (S x S) will likely be less screwed than a double dilute with a lot of white (sw x sw). I think there was also mention of a correlation between facial white & hearing/eye defect. As so in theory a double dilute collie (a breed where the blaze has largely been bred out of the gene pool) would tend to fair better than a double dilute Sheltie (a breed where blazes seem to be much more common.
I can’t recall where I read this paper because I would love to double check the info.
I have collies and personally I don’t think there’s ever a good reason to breed two merle together. That said, I’ve met one double dilute collie in person who could see & hear normally enough though I don’t believe he was formally tested. He was certainly lucky. OTOH, I’ve met two double dilutes of other breeds (Dachshund & Aussie) who were both totally deaf & blind. Both had dedicated owners who were willing to put in the extra work.
What kind of life is it for a dog that’s deaf and blind, though? Is having only a sense of smell and touch enough for them to have a fairly normal dog existence?
I think a dog with only a sense of touch and smell could be very happy. I think people often overvalue capabilities and their relevance to happiness. For example, my grandma doesn’t remember anyone around her and her husband thinks that makes her sad. However, I have observed that she is a lot happier now, in her nineties, than she was in her seventies, when she was very intelligent. I think a lot of people don’t do a good job of understanding their handicapped loved ones whether they are human or canine. We often imagine that they are sadder than they are or we remember them as being happier before than they ever were.
Lochinbrae BCs recently posted..This will be the father of our litters who will be born April They will not be ready to leave home until June
The only difference is, in humans, these conditions are just bad luck. In dogs, we deliberately subject them to selective breedings.
Dave recently posted..Peanut Butter Is Not a Lie!
Often an elderly human becomes blind or deaf at an extremely advanced age. If a dog went blind after ninety years of health we would not call that bad luck. There are enough differences that it is difficult to make this comparison between dogs and humans.
A week ago I ran into a great dane who was a double merle. I could tell his coloration because of the way his eyes looked. The breeder who had kept the dog herself explained that both of the parents where harlequin (her name for merle). His disability was that he could not hear most noises. But he seemed quite content and happy.
I do not agree with breeding two merles, but I don’t know if I want rules or laws regulating the practice. Personally, I would not want to keep any merle from a litter since even a single allele can produce some hearing impairment. Admittedly, I find the merles, whether single or double, to be very beautifully coated. But there are a lot of other great colors that don’t have any drawbacks.
Lochinbrae BCs recently posted..Sacramento Dog Show
* I’m not advocating laws, such things are not practical or enforceable really. Breeders can lie and by all means they do. I’m more inline with the “provide education” especially to the buying public, but to breeders as well. Other breeders are spreading such horrible information, sometimes outright lies, on their websites, it’s worth lighting a candle.
* I think Dave was referring to congenital diseases, present at birth in humans, not so much the degrees of deafness/blindness due to aging.
I’d add that in humans, even when we do know about our genetics, we can make informed decisions from experience. In the case of deaf parents choosing to have children who might be deaf, we can weigh self determination and genetic rights against their own experience… we don’t give dogs the same choice. We don’t ask them if they are willing to be deaf to sport a certain style of coat, we can’t ask them if the risks are worth taking.
* Merle is very beautiful, but I have found that my fondness for it has decreased aesthetically with my increased knowledge of its health effects. I’ve always loved me a classic B/W Border Collie anyway. The colors we’ve produced at stud are fun and amazing, but seeking color has played no choice in my breeding choices. For all I knew before they were bred, Dublin and Mercury carried no color variants (except for Tri, obviously) and that was perfectly find with me.
Two different genes it has been discovered can act together to modify and create multiple phenotypes. The new scientific findings that go beyond Mendalian Genetics is being ignored.
Oh, and “Harlequin” is having both Merle and the Harlequin modifier gene. So although you can be Merle without being Harlequin, and dogs can carry the Harlequin gene without any visible sign (if no merle is present), Harlequins are always a combination of both. That’s a LOT of color knockout genes.
I haven’t done a post yet on the Harlequin gene or Piebald gene, but I’ll get on that as at least one of them is present in Border Collies and Harlequin is also a lethal semi dominant.
Eh, I was thinking of how the Nazis forced blond “fit” German women with their own SS elites. We have the blessing of choosing our own mates, being burdened by the consequences of our choices, but dogs still are anchored to what the Nazis did to their own citizens in attempt to colonize Poland.
Dave recently posted..Inus and a Hog
So unless one wants to talk about Lebensborn, it’s fallacious to compare animals to humans, and if we go down that route… we will get into the Bible; particularly the Genesis about whose domains belong to who.
Dave recently posted..Inus and a Hog
What is the point of working with animals who pass along lethal, or semi-lethal genes on purpose? You’re talking about how a dog who was deaf and blind and it was known that could happen, but done anyway? For what? A mere color?
Animals don’t know how to do anything but compensate for whatever happens to them, so they keep living. Dogs can’t think about being happy, they simply are and keep on living regardless of what happens to them, but we have a lot of control over what we breed and we know what we’re consigning them to a lifetime of.
I knew of a breeder of Dalmatians who produced deaf dogs and kept on doing it and told people that even deaf dogs could have good lives and even told them how to train them, so people gladly paid for deaf dogs so they could be giving the dogs a good life, when they didn’t ever have to be produced in the first place! That’s completely different from a deaf dog happening by mistake, that one didn’t know could happen and then being given away, neutered, never to be bred from.
How could a coat color be so important to humans that they will breed for it even knowing bad things can happen with it?
So in light of the C189G mutation, does that means the double merles born without an anus are unfortunate victims of being a double homozygous for semi-dominant genes?
Dave recently posted..Peanut Butter Is Not a Lie!
It’s quite possible. Those poor Aussies might be double for both genes and the inperforate ani might be due to the stump tail gene instead of the merle gene. I’m not sure that the causative factor in the merle -> closed anus effect has been identified. We have a pretty good idea on the merle -> deafness mechanism.
Here’s a Catahoula that is said to be Double Merle, but it could be Double Bobtail, or both.
http://handicappedpet.net/helppets/viewtopic.php?f=29&t=13347
Anal deformities (and general lower-body defects) are commonly recorded in animals bred for bob-tail genes (rats, cats, and dogs). It seems to me that the bobtail gene is a more likely cause than the merle gene.
Found out most, if not all, of the cur landrace are known to harbour the bobtail gene.
In fact, there’s a breeder in Ontario who deliberately breed for natural bobtails:
http://www.bconnex.net/~langevin/
Dave recently posted..The Briton
http://www.steynmere.com/DALM_DEAFNESS.html
My first introduction to pigment and deafness was via the Dalmatians high incidence of deafness. 5% to 20% of live births. I was stunned.
The true irony was revealed when it turned out that the pursuit of the “perfect coat” was the root cause. Dalmatians are essentially white dogs with spots, and the lack of pigment is what causes the deafness. I stopped loathing Cruella de Ville for coveting puppies for their pelts when I realized that the breeders themselves coveted those pelts just as much….and likely culled more “defective” puppies than the fictional Cruella ever planned on doing.
Reading up on Dalmatian studies and research is a bit discouraging because of the ignorance it reveals. One study bred unilaterally and bilaterally deaf dogs together and was surprised that the results didn’t show a strong correlation. Studies of blue eyed dogs did show a consistent correlation – naturally, lower pigmentation leads to both blue eyes and deafness. A bit sad to see any study that hopefully puts forth a theory that deafness could be minimized by not breeding deaf dogs, when the basic concept of the breed itself will result in deaf dogs.
I think this statement is incorrect:
“Some Shetland Sheepdog breeders in an attempt to create an all-merle line (if not a separate breed entirely) that always produced 100% merle puppies (to “breed true”) bred from several double merle sires that were apparently asymptomatic for merle related diseases.”
There have certainly been a tiny handful of double-merles at stud, I can think of maybe 2 or 3 in 30 years of studying the breed, but the reasoning was never to create a separate breed or a separate line of that color. The breeders involved understood the genetics of double merle and had the resources to keep and care for any defective puppies. Their goal was to predictably produce offspring from those dogs with one merle gene. I don’t breed any kind of merle personally but all the merle shelties I know are healthy and happy dogs. I would be curious to know if any hearing deficit affects them because the success of merle shelties in herding, agility, and other activities that require good hearing is easy to see.
It is uncommon for sheltie breeders to even consider creating double merles. If someone actually misunderstood genetics enough to try to create a closed, all-merle or double-merle gene pool with shelties I would assume they were a “puppymill” or some kind of fly-by-night backyard operation.
I’ll refer you to the following:
[source]
and
[source]
I’d like to see some evidence that these two breeders back in 1980 understood the double merle gene, knew it was semi-dominant, and knew that it caused horrible deformities.
The clincher is this:
[source]
Again, “the only breeding that will reliably produce more than 50% merles” … “homozygous merles are…useful for producing merles.”
This website is clearly not under the same illusion that you are: the reason to PROMOTE and use (to the point of being extremely popular sires) dogs that can not even be shown, is to produce all merles. It doesn’t need to be common to create these dogs, popular sires aren’t common, most breeds have only a small list of dogs that are way over used. It seems that Shelties have (at least) three way over used sires. I’d love to see if you can show me that these dogs were special in some other means tan their extreme whiteness. That they were popular for another reason than “I want all merle puppies!”
And do you think herding and agility are really evidence against hearing problems in merle dogs? Please, show me a hearing study. Irrelevant anecdata is worthless. I don’t think you can really even document the rather vague statement anyway. Hearing loss isn’t easy to see, you know, because it’s sound.
And don’t try and blame puppy mills, sorry dear, I don’t think that these three “ROM” popular sires were treated by the Sheltie gene pool as fly-by-night “backyard” operations. The sins of the show world have been blamed for too long on some mysterious “BYB” … no, this is not an issue attributable to the faceless BYB, these dogs have names, sired tons of dogs, numerous show champions, and are lauded and celebrated by the toast of the Sheltie community.
Know this is old, just happened to come across it. Yes, merle to merle breedings in Shelties have long been a source of controversy. I knew of it when I first researched the breed in the mid-70’s (I was 13 years old when I got my first Sheltie, and being the bookish type, wanted to learn about the breed). I did punnett squares in Biology class with Sheltie color genetics in mind.
And yes, there have long been breeders who will deliberately produce a merle x merle litter (NOTE: I DO NOT APPROVE OF THIS–I AM ONLY CONVEYING FACTS). A merle x merle litter is not necessarily going to produce all double merles, either by punnett square or by experience–since merle is a modifier, it’s possible (and likely) that you will also get heterozygous merles and non-merle tris or bi-blacks (interestingly, there’s still more of a taboo against breeding sable merles–I’ve never heard of a homozygous merle with one or both parents a sable merle).
All THAT said, there’s a case to be made that overused double merle sires are really messing with the performance potential of AOAC (any other accepted color–IOW, not sable) Shelties. It’s somewhat common knowledge among those of us who care about these things that descendents of certain double merle sires are more likely to show up with Early Takeoff Syndrome–which pretty much dooms them as competitive Agility dogs.
I totally like this article but I quibble with the use of the term “lethal” for the merle gene. http://ghr.nlm.nih.gov/glossary=lethalgene0 Doubling up on the merle gene *can* result in death, but not necessarily and probably not in most cases (since, if that were the case, a MmxMm litter would produce fewer live births of MM puppies than the predicted 25%, and this does not appear to occur, i.e, plenty of live MM pups are born).
This is different from the bobtail gene, where homozygosity IS lethal prenatally.
I am not saying this to promote merle breeding in any way. I’m just a born quibbler. For example, I can totally understand how this idiot thought it was important to specify “marten” when his victim asked why he was carrying a weasel. http://www.usatoday.com/news/offbeat/2011-06-08-dead-weasel-assault_n.htm
Lethal: Sufficient to cause death
Fatal: Causing death
Like in LD50 with toxins and venoms: it may not cause death, but it’s known to if in high enough doseage. Pick your poisons. Throw the dice.
Dave recently posted..The Queen Anne
A breeder on the Yahoo Performance Collie list took exception to what I wrote here and ran it by a geneticist who worked on the Merle and Harlequin gene mapping.
I still don’t have an answer how I misrepresented George Strain, and I link to his paper in this post so you can read it for yourself.
I was incorrect in the comments here when I said that Harlequin = Merle + Piebald. In fact, it’s actually its own separate gene, so the visible Harlequin pattern is actually Merle + Harlequin. You apparently can’t see the effects without having Merle present as well.
Harlequin is, according to the paper, a letal semi-dominant as well. No good!
So, I’ll take the geneticist’s seal of approval and correction on the article. Rational adults can admit errors and look at data and change their minds. Luckily my error here was minor, conflating the piebald gene with the harlequin gene (and done before the study identifying the gene even came out), and no change of mind is really needed on the substance of the issue.
Merle is still a lethal semi dominant, and so is Harlequin. Breeders should be aware of these effects when making ethical and practical breeding decisions.
Christopher recently posted..The Dog Days of Summer
The coauthor of the Dr. Strain’s article who has a PhD in animal genetics is sending me the most recent research info on any misinterpretations on your part, Chris. She knows her own research; I’m guessing you’ll agree on that much. I will read it, quote it and try and explain how you have misinterpreted it. If I have trouble with that task, I’ll contact the authors themselves for help and let you know.
Your single copy Mm gene info is most definitely incorrect. The most recent research disproves it. The German study used dogs listening to radios as their proof – for God’s sake! There are actual pictures of that part of the so called “study.” That’s how we’re proving deafness in heterozygous merles – you’ve got to be kidding!
The Aussie photo on this page is lifted – it’s copyright protected and belongs to the researchers. Be careful. I always cautioned my students over 30 years of teaching research about copyright violations.
http://pets.groups.yahoo.com/group/percol/message/12715
http://pets.groups.yahoo.com/group/percol/message/12767
Hungarian Border Collie board
http://netboard.hu/viewtopic.php?topic=21823
there is a project, ongoing with the catahoula set in regards to merle the findings have been rather interesting i thought you might enjoy reading themvhttp://www.cobradog.com/current-projects.php
They’ve done a lot of looking on it and now recently in catahoulas there are dogs that don’t even have a spot of white on them and solid dogs being born deaf or blind.