Semi-dominant alleles are those that are less potent in heterozygous form (one copy) than they are in homozygous form (two copies), but which are potent enough to show a difference in phenotype from the wild-type allele (no copy). Recessive alleles show no difference with only one copy versus zero copies, and fully dominant alleles look the same with one copy as with two.
A lethal allele is a variation of a gene that will eventually cause death, perhaps even a failure of conception or birth.
Such is the case with the most common allele which results in a natural bobtail. This gene has been documented in a number of breeds including: the Australian Shepherd, Austrian Pinscher, Australian Stumpy Tail Cattle Dog, Braque du Bourbonnais / Bourbonnais Pointer, Brazilian Terrier, Brittany Spaniel, Croatian Sheepdog, Danish Swedish Farmdog, Jack Russell Terrier, Karelian Bear Dog, Mudi, Polish Lowland Sheepdog, Pyrenean Shepherd, Braque Francais / Savoy Sheepdog, Schipperke, Spanish Water Dog, Swedish Vallhund, and the Pembroke Welsh Corgi. It has also been intentionally introduced into the Boxer to keep the look of a docked tail in countries that have outlawed docking.
Congenitally short-tailed dogs are present in many breeds; however, the causative mutation located in the T-box transcription factor T gene (C189G) had only been described in the bobtailed Pembroke Welsh Corgis. We investigated here the presence of the T gene mutation in 23 other breeds (360 dogs, including 156 natural short tailed) in which natural bobtailed dogs exist. In the 17 breeds in which the C189G mutation was observed, there was a perfect correlation between this mutation and the short-tail phenotype. However, 6 breeds did not carry the known substitution or any other mutations in the T gene coding regions. No dogs were found to be homozygous for the C189G mutation, suggesting that the homozygous condition is lethal. In order to study the effect of the T gene mutation on litter size, we compared the number of puppies born from short-tailed parents to that born from long-tailed parents. In the Swedish Vallhund breed, we observed a 29% decrease in the litter size when both parents were short tailed.
The Boston Terrier, English Bulldog, King Charles Spaniel, Minitaure Schnauzer, Parson Russel Terrier, and Rottweiler exhibit natural bobtails but do not carry the C189G mutation, and the following breeds have not been tested to confirm what mutation causes their bobtails: the French Bulldog, McNab, Miniature Fox Terrier, Old English Sheepdog, Rat Terrier, and Tenterfield Terrier.
Like Merle and one of the Hairless alleles, the C189G mutation is considered semi-dominant and lethal, but unlike those other two, there has not been scientific observation of negative health effects (other than the lack of a tail obviously) in dogs with only a single copy:
In contrast with homozygous, heterozygous bobtailed dogs have not been reported to manifest any other abnormalities (Indrebø et al. 2007).
While some breeders are claiming that the bobtail gene is also superior to the other known lethal semi-dominants in that it does not produce live homozygotes (“it only hurts eggs”), there are documented double bobtails that have been born with severe deformities:
Recently, Pembroke Welsh Corgi puppies with severe anatomical defects having the homozygous mutation have been characterized. These puppies lacked tails, manifested anorectal atresia with severe alterations in the posterior lumbar region and spine, and had a failure to thrive (Indrebø et al. 2007).
So beyond the ethical implications of killing embryos (out of sight, out of mind for most breeders), the double bobtail allele can produce profoundly crippled live births. The ethics of this are a bit more problematic. Although given that other scientific inquiries were unable to account for surviving double bobtails, it’s likely that the homozygous form is particularly lethal resulting in only a small percent of surviving puppies. Unlike some theories that these fatalities have little or no effect on litter size (the assumption being that the embryo would fail early enough for another non-homozygote to thrive in its place), the above referenced study did show a nearly 30% reduction in bobtail x bobtail litters. Sadly, they didn’t report on bobtail x tail fertility.
Without a healthy example of a double bobtail, the most concentrated we can breed to maximize the number of bobtail puppies is Carrier x Carrier, as documented in the diagram above. The lack of a healthy homozygote for bobtail gene means that this mutation will never be able to provide a completely bobtail strain that breeds true. There will always be a 33% undesirable overhead (dogs with tails) in any bobtail breeding plan. If we chose to consider the lethal homozygotes as well, there’s a 50% undesirable overhead in the effort to breed bobtail dogs with this gene. I think that’s a significant enough percent to question the ethics and efficacy of a genetic solution versus a surgical one.
Adorable Corgis provided courtesy of Cartoonize My Pet.
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Or to use the bulldog short-tailed gene.
retrieverman recently posted..Identify the newborn puppy
“So beyond the ethical implications of killing embryos (out of sight, out of mind for most breeders)”
This particular argument is one to be very, very careful of. Studies in pregnant laboratory Beagles had a resorbtion rate of eleven and thirteen percent, respectively. A study in street dogs in Mexico showed that resorbtion is very common, regardless of body condition. If you are going to even broach the possibility of resorption as an ethical issue, it must be applied to all canine pregnancies, due to it’s commonality. Pretty much every pregnant dog has at least one dead ‘puppy.’
Jess recently posted..DesertWindHounds Will be on Haitus
Don’t get me wrong, I’m not making an “every sperm is sacred” argument. If I wanted to go down that path I’d devote more than a sentence to it.
The ethical consideration here that is of interest to me is, as Dave points out, that we KNOW this is happening and we know it’s because we’ve chosen to select for this one trait. And Scottie points out the solution: use the other bobtail gene, bob surgically, or don’t bob at all. And the downside for me, ethically, isn’t so much that blastocysts die (I don’t believe little puppy souls are going to flood doggy heaven), but that the resulting decrease in litter size we see in some studies is a high price to pay for such a small benefit.
The ethics of this is that you can only lop off 25% of your fertility rate so many times before you’re fundamentally changing the equation of how dog breeding works. With so many other deleterious recessives in play, the litter model is really the only thing that will allow a successful future. If we breed down to a “one puppy policy” situation biologically, we’d have to get rid of a lot of the bad recessives first or face a worse situation than we have now.
It’s a 25% chance -each time an egg is fertilized-, not 25% of the total litter. In many cases, a homozygous pairing won’t even occur at all during a pregnancy.
Well, over many litters those two concepts will converge. A 25% chance per puppy will average out to a 25% decrease in litter size over a large number of litters. You might have a run of very healthy or very diseased litters, but over all litters, the 25% will hold. It’s not a guarantee in any one litter, but if it really is the controlling factor, it will most certainly be descriptive of the sum of all litters.
This is why I’m confused by the complete (as far as I know) denial among Pem breeders that homozygous bobtails are born at all. It would not be something that could be missed, if it truly occurred consistantly and demonstrably because both parents had the bobtail gene.
But you can’t deny that the paper has them clearly recorded. I don’t know what to make of that.
Theoretically you cut the fertility rate every time you produce a litter and are not selecting for fertility. On *that mailing list* there are many posts about lower litter sizes over time. Many breeders don’t even get too excited about it because it means less pups to place. Lots of things will affect the fertility rate, from inbreeding to diet. Are there enough bob/bob litters produced that you are actually going to see an across the board reduction in litter sizes? IOW, are there enough bob/bob litters being produced to actually affect the number of puppies produced by the breed as a whole? And does that actually matter, if the vast majority of those pups are going to be speutered anyways?
Jess recently posted..DesertWindHounds Will be on Haitus
I don’t know what sort of mechanism would shrink litter sizes unless you actively (or accidentally) selected against size. If you’re selecting neither for or against something, it usually just drifts.
Inbreeding blindly and selecting for deleterious recessives, of course, is “accidentally” selecting against health, vigor, litter size.
I don’t see smaller litter sizes as any benefit though given how PICKY the fancy is over what they want in a pup. Smaller litter sizes means that they are less likely to get what they want, and it’s possible that this could result in more litters.
For instance, let’s look at the Aussies who have a fetish for both Merle and Bobtail. If we bred a dog with both to another dog with both, 7 out of the 16 possible outcomes would be fatal. That’s throwing away a lot of desirable dogs.
I think I’ll do a post on it. Poor Aussies.
Heh… trying to rile up the Religious Right, Chris? See if you can get the pro-life people to pickets fanciers?
Dave recently posted..Peanut Butter Is Not a Lie!
Heh, the Bible does not speak too kindly about dogs, so I’m not sure the fundamentalists get as uppity about fruitful and multiply about puppy fetus. The comparisons don’t really apply, dogs are property and if we want to get human about them, the whole thing sounds horrific, sort of like the PeTA platform… trafficking in offspring (from forced rape) that are put to work… blah blah blah
Weirder interpretation had happened…
Dave recently posted..Peanut Butter Is Not a Lie!
I’m not Pro-Life when it comes to dog zygotes. I care more about the quality of life of actual living puppies and dogs, not the few pre-fetuses that don’t make it past embryogenesis.
If that makes me a monster in some people’s eyes, so be it.
Considering that the blastocysts don’t even implant until 18 days or so into the pregnancy, yeah, not too worried about them. I’d really prefer that enough of them kick the bucket so that there’s not too many pups born. Not a big fan of giant litters.
Funny thing is, breeders are finally realizing that some resorbtion is a normal part of dog pregnancy because so many people ultrasound now, and it’s sensitive enough to pick things up quite early.
Jess recently posted..DesertWindHounds Will be on Haitus
Even in humans, something like 2/3 of fertilized eggs spontaneously abort early on: http://discovermagazine.com/2004/may/cover/article_view?b_start:int=2&-C
Something which puts a damper on the ‘fertilized eggs are equal to full human beings’ crowd. Someone who doesn’t use contraception actually kills more fetuses than someone who does. =P
I’m frankly shocked that stillborn homozygous Corgis are born. I can’t reconcile that fact with statements like these (which are universal in Pem circles): http://anne.kleivens.com/annwn/bobtails.php
But just looking at the variety of tail lengths and the description of the homozygous pups in that study, it appears to me like the bobtail gene in Corgis might be similar to the Manx mutation in cats, in which the risk of stillborn/defective kittens is well known and admitted by breeders, and regular crossing to tailed cats is considered the responsible thing to do. But I can’t fathom that there is some kind of breed-wide Corgi conspiracy to cover up the fact that homozygous bobtails are born. They must be very rare, and it must not be visibly obvious as to the reasons why the pup died.
Discussion about taillessness in animals in this video.
retrieverman recently posted..Old type Neapolitan mastiffs
You can add the Spanish Mastiff to the list of breeds that have the bobtail gene, it is found in old working lines, as the Mastiff Club decided to not accept them (Clubs and their “great” ideas…). Here you are some pictures of bobtail Spanish Mastiffs:
http://img15.imageshack.us/my.php?image=sanson.jpg
http://img685.imageshack.us/img685/5903/rabondepecho2.jpg
http://imageshack.us/photo/my-images/820/110421010.jpg/
http://i55.tinypic.com/3148p6c.jpg
pets.groups.yahoo.com/group/MAS_Health_Genetics/message/56
I went back to this post recently after googling Australian Stumpy tails, which people who breed them seem very intent on distinguishing from ACDs, on bases like no tan points ( because no kelpie in the background), longer legs and a leaner build, a finer head, than the ACD.
But in site after site, under health concerns, I only found one that mentioned what could be an issue due to the tail, and “spina bifida” was cited. Pic after pic of stumps are seen. If these people are breeding bobtail to bobtail all the time, I would expect lots of problems. And if that’s the case and no one is talking about it, I find that pretty scary.
They know they just refuse to talk about it. I know so many Stumpy breeders who breed stumpy to stump & only get a couple pups & the over all odds are no better.
Even the old timers knew t breed at least stumpy to rumpy.
This is a very biased article to attempt to get people to believe that breeding for NBT is heinous. However, you fail to mention that out if the hundreds of corgis bred over and over and if the many breeds and thousands if dogs tested, only 2 corgi pups were born that carried the homozygous T-box gene. Further, any study that finds a decrease of 30% live births in mating 2 natural bobs together would be suspect since 25% at most would be statistically maximum. Further, other studies have reported from 0-17%, but you make no mention of those nor of the validity of the study you do mention. For those who jumped on your bandwagon, spina bifida in humans has been found to be related to a lack of a certain vitamin, not genetics and may be so in dogs as well. Personally, over 30 years of breeding Aussies, I have bred many very short NBT together and had no issues with the pups born. If my litters are smaller, it was unnoticeable and would have to carry out a statistical analysis before determining if there was any significant correlation between the gene and the number of offspring. It’s articles like these that set dog breeding back decades before real research was done.
> This is a very biased article to attempt to get people to believe that breeding for NBT is heinous
This is actually a pretty straight forward article supported by facts that doesn’t whitewash NBT because ignorant breeders made it part of their breed standards.
> you fail to mention that out if the hundreds of corgis bred over and over and if the many breeds and thousands if dogs tested, only 2 corgi pups were born that carried the homozygous T-box gene
Thousands of dogs tested? Where do you get such data? You’re just making that up. NBT DNA tests are a relatively new thing and for most of their short history very expensive and out of reach of most non-scientists. So tell me where are all of these thousands of dogs recorded? There has been no comprehensive study that tested numerous litters as they were born to see just how many homozygous NBT puppies survived to birth and how many of those were failures vs. how many were healthy. It hasn’t been done, so it’s ludicrous that you’d claim some great investigation has been completed.
> Further, any study that finds a decrease of 30% live births in mating 2 natural bobs together would be suspect since 25% at most would be statistically maximum.
You clearly don’t understand statistics or the definition of the word maximum. Twenty-five percent would be the expected value, the average, not at all would it be the maximum. Nor does 30% ring any “suspect” bells. Observing 30% when you expect 25% isn’t even likely out of the first confidence interval let alone suspect. You can actually run analysis which would ferret out how unlikely the observation vs. expectation is and if the observation is suspect, but doing so is likely way over your head.
Even basic logic doesn’t make 30% unlikely. In a womb where 25% of the fetuses die, there is likely a spill over effect where occasionally other fetuses would be compromised for any number of reasons. A dead fetus in one of the first positions could stall birth and compromise later fetuses, or perhaps being next to one or more dead fetuses would increase the chance of failure.
No statistician would be so stupid as to assume that the survival rate of fetuses within the same womb are wholly independent events.
> Further, other studies have reported from 0-17%
Name them and let us have a look at their methods. And note, absence of proof is not proof of absence.
> It’s articles like these that set dog breeding back decades before real research was done.
LMFAO. You’re a stupid monster. How has anything I’ve ever written SET DOG BREEDING BACK in any way? I’ve never once advocated for anything that would harm a dog. And yet here you are claiming that being truthful and fact based about a disease gene that amputates a dog’s tail in one dose and causes death with two is somehow ADVANCING dog breeding? What a callous fool you are. What horrible things you do to dogs for what benefit?
You Aussie breeders are a real trip. You double down on merle and bobtail, two needless and debilitating genes, because you think it’s pretty? Seriously, you’re a monster.
Well said
Christopher, I did some up to date reading after learning of a Boxer breeder who breed a Corgi for the natural bob tail to avoid docking.
It turns out a different mutation causes the short tails in Bulldogs and Bostons versus Corgis and Australian Shepherds, for example. The mutation in Corgis is called a T-box mutation. of the 23 breeds in which natural bobs were found, 17 had bobs caused by this T-box mutation.
These included the Australian Shepherd, Brittany, Karelian Bear Dog, Polish Lowland Sheepdog, Pyrenean Shepherd, Schipperke, Swedish Vallhund and Russell Terrier. In each of the dogs of these breeds with natural bob tails, one (and only one) copy of the T-box gene was found.
These findings indicate that the bobtail mutation acts as a dominant trait, and suggest that having two copies of the mutation is lethal. In fact, the T-box mutation in mice is known to cause embryonic death. Turns out the same is true for dogs as your article points out. .