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Coton de Tulear Talls

TALL.cotons.bookWe now turn to a real life story of genetic research in action.  The fascinating story of Tall Cotons de Tulear.  There have been some exciting changes in the world of TALL Cotons since the book was published in January, 2002.  These revisions are shown in red below...

Tall Cotons [1]

Picture a Coton with exceptionally long, graceful, gazelle-like limbs--first observed in Coton de Tulear litters in Madagascar, then America, then Europe.  It is, without question, the rarest of all Cotons.  It remains not described by any Standard, although both M. Petit, who wrote the original FCI Standard and myself, who authored the CTCA Standard, mentioned the variety in print more than a quarter century ago.  Tall Cotons have been born in both genders and all three colors, (White, Black & White, and Tri-color).

A Tall Coton, though larger than a standard height Coton, is not "big."  There have always been standard Cotons that exceed the CTCA's maximum weight allowance, and there have been Cotons that are slightly larger in all dimensions than the CTCA Standard calls for.  Instead, a tall Coton is lithe and normally lean--it appears especially light, graceful--even fragile in aspects.  They are reminiscent of gazelles or antelopes.  A Tall variety Coton stands between 15 and 17-inches at the withers (shoulder).  Alika Cotons[2] placed seven tall Cotons during 26 years of breeding Cotons.  Oakshade Cotons (1974-1994) produced two Tall Cotons.  All have been devoted, healthy, happy dogs.  They are confident and outgoing, but none have had a domineering personality.  In short, Tall Cotons do not appear to suffer the "short man syndrome."lucy

Make no mistake, the Tall Coton de Tulear is 100% a Coton de Tulear, not some hybrid creation.  In fact, a Tall Coton is always born within a normal litter of Cotons, to parents of normal height.  Since Tall Cotons are extremely uncommon, it suggests that they are the result of a mutation in the gene(s) that primarily controls the length of a Coton's limb bones--specifically a gene that controls the growth of the body's long bones.  Such a mutation predates modern writings about the breed.  Today, the allele(s) that create a Tall Coton de Tulear remain a mystery.  But some cooperative CTCA breeders may soon solve the puzzle.


The Hypothesis

An experiment requires an hypothesis to test.  An hypothesis is a fancy term for a statement about some aspect of the natural world.  It is a "straw man," constructed in such a way that a test, (or several tests), can actually refute it.  Then, the experimenter conducts observations that can refute the hypothesis.  If the hypothesis survives the test(s) and is not refuted, we have reason to accept the initial hypothesis as a valid interpretation about how some aspect of nature works.  Clear as mud?  It is really quite simple: propose an hypothesis, test it, then either reject it or provisionally accept it.

From observations of previous matings that have produced Tall Coton pups, we find that:

  • certain mated pairs of normal Cotons produce a high frequency of Tall pups;
  • so far, these parents have not produced Tall Cotons when mated to other Cotons;
  • Tall Cotons have been of both genders and all color varieties, and;
  • when tall pups appear in a litter they comprise between 20% and 50% of the pups in the litter.

These observations strongly suggest, (but they do not prove), that the trait "Tall" is the product of autosomal, recessive inheritance that is not linked to genes that produce color.

Autosomal Inheritance

For every particular genetic trait, every mammal has two forms of every gene.  These forms are called "alleles".  A fetus gains one allele from its mother, (it was present on a particular chromosome in the unfertilized egg), and the other from its father, (it was present on the homologous chromosome in the sperm).

Alleles are found on chromosomes, and each chromosome pair can be identified as unique--carrying a unique set of alleles.  Most chromosomes are called "autosomal", meaning that they have nothing directly to do with determining gender.  Gender is determined by the so-called "sex chromosomes", which in mammals are termed the "X" and the "Y" chromosomes.  Two "X" chromosomes create an infant female; an "X" and a "Y" chromosome make a male.  The Y-chromosome is tiny, and it does not carry all the complimentary alleles that are found on the X-chromosome.  Hence, inheritance of traits that are found on the gender-determining chromosomes is gender-biased.  No such strange correlations between gender and a trait normally occur when the alleles for a particular trait are found on any of the autosomal--non sex-determining--chromosomes.  Most alleles are autosomal.  The dog has 38 pair of autosomal chromosomes and only 1 pair of sex-determining chromosomes.  For comparison, humans have 22 pair of autosomes and, of course, only one pair of sex-determining chromosomes.

Recessive Inheritance

We think, (guess; hypothesize), that the "Tall Coton gene" is located on an autosomal chromosome, we also have reason to suspect that the alleles that produce or fail to produce the trait behave in a "classic" dominant-recessive fashion.  That is, one allele will be expressed and its opposite allele, although present, will not be expressed.  Further, one allele--the one that produces a normal height Coton--is dominant and whenever it is present, it will be expressed.  So, a normal height Coton will be produced whenever it has one or two alleles for normal height, i.e., "H//h" or "H//H."  It is possible that the homozygous dominant genotype "H//H", will produce a somewhat shorter, longer-backed Coton de Tulear, but that observation remains unconfirmed.

Note that a perfectly normal looking Coton may be carrying the allele that codes for tallness.  Your Coton, in fact, may be a carrier of this trait, i.e., your Coton may be heterozygous, "H//h." Allele "h" just isn't expressed because your normal height Coton developed under the control of its dominant, "H" allele.

Only when two alleles, (let's call them "h"), that code for a lengthening of the long bones are present will the Coton actually be tall.  These alleles are recessive: If so, then: allele "H" codes for a normal height Coton and is dominant; allele "h" codes for a Tall Coton, but only if the Coton has what is termed a "recessive homozygous genotype," i.e., "h//h" -- one "h" allele from each parent.

Predictions (an Hypothesis)

If two normal height Cotons mate and if one is a carrier of the recessive tallness allele, (H//H x H//h), we predict that no Tall Cotons will be produced, albeit 50% of the pups in the litter will be carrying the tallness allele, (H//h -- shown as lightly shaded, below).  Note that the alleles contributed to offspring from one parent are shown on the left column, (H/ and H/); the alleles from the other parent on the top row, (H/ and h/), see Figure 1:

GENES.665.punnets

If two normal height Cotons mate and if both are carriers of the recessive tallness allele, (H//h x H//h), we predict that approximately 25% of the litter will be Tall Cotons, (h//h -- shown as darkly shaded, above, Figure 2), and 50% of the litter will be normal height carriers, (H//h -- shown as lightly shaded, above), and 25% of the litter will be normal height non-carriers, (H//H -- shown in the unshaded, upper left box of the Punnett Square above, Figure 2).

We hypothesized that Josephine, (Alika's Josephine Pernel of Oakshade), and Napoleon, (Alika's Napoleon Felix of Oakshade), were carriers of the tallness allele (H//h). However, their days of producing puppies are at an end.  Napoleon has died.  Hypothetically, Josephine, when mated to another male, might never again produce a Tall Coton, (unless the male also is carrying an "h" allele). ,Yet, Josephine, a carrier of one recessive Tall allele (h), has produced Tall Coton pups when mated to other males, indicating that the tall allele may be more common in the general population than we previously suspected.

We have observed matings which could easily be explained by the two preceding diagrams.  We predict that if two Tall Cotons, (h//h x h//h), were mated, all offspring would be necessarily Tall.  It is possible therefore, that the Tall variety Coton de Tulear could breed true with it's first and subsequent litters--an exciting experiment which would further test the hypotheses about the inheritance of the Tall Coton phenotype.

 

The Tall Coton Breeding Experiment

Alika Cotons has initiated a special breeding program that aims to determine the mode of inheritance for the tall trait.  Over the years, we, (and other breeders in Madagascar, Europe, and North America), have produced some tall Cotons but, to our knowledge, none were ever bred to one another.  The tall Cotons produced by Oakshade Cotons and Alika Cotons were neutered.  We placed a tall Coton that was sold under a special contract and classification.  This Coton cannot be bred without following the experiment's protocol.  Lucy is classified on her Official CTCA Pedigree and Registration, after passing her mandatory CTCA Health Tests, as "Breedable--Tall experimental".  In 2002 and 2003, we and other CTCA Code of Ethics Breeders have produced and placed Tall, Potentially Breedable Cotons.

The experimental protocol is designed to couple unrelated tall Cotons.  For example, the mate for Lucy must conform to the CTCA's rule permitting a mating which will only produce pups no more than 15% inbred, (using Wright's Coefficient of Inbreeding). Once a suitable, unrelated mate is found, and a proper breeding contract is signed, a mating can take place.  Even so, all pups so produced must be sold as either "Potentially Breedable--Tall-experimental" or "Pet Quality--Tall.".  The goal is not to exploit experimental matings, but to learn.

For the present, then, we are searching for unrelated, un-neutered male and female tall Cotons to produce the first Tall x Tall litters.  Coreen Savikko, who has produced tall Cotons in the past, is currently hoping to produce a suitable mate for Lucy.  We are obviously some years away from an answer to the questions proposed here, but with additional Tall pups being located and Health Tested--Passed, it is only a matter of time.

However, in 2003, we instituted an important and fruitful change in experimental protocol which has allowed us, (and soon, others), to produce additional, Potentially Breedable Tall Cotons.  With the club's permission, a breeder may now mate a Tall Breedable Coton with a Standard Breedable Coton who is a known carrier of the Tall allele, i.e., who has produced a Tall pup in one or more of his or her previous matings.  In June, Long Tall Sally of Alika Cotons gave birth to a litter of seven mostly Tall Coton pups sired by Rossy of Crabapple Crossings, a Standard male Coton who had produced Tall Cotons pups previously when mated to a Standard, carrier Coton female.  Thus far, these results are consistent with accepting the hypothesis that the Tall allele is a discrete, autosomal recessive gene.

The Future

It is conceivable that someday, if the genetics of the Tall variety Coton de Tulear are understood and confirmed, a Standard could be written to support their breeding.  If that were to happen, then the Tall variety Coton would take its place as a duly recognized size variant of the standard Coton de Tulear breed, much like the recognized size variants of some other breeds, (the Schnauzer, the Mexican Hairless, German Spitz, Poodle, etc.).

For the present, we can understand why the few families who have a tall variety Coton and those of us who have been privileged to know a tall variety Coton will occasionally view the standard-sized Coton as "Vertically Challenged."

Do you have information, comments or questions about a Tall Coton you can share with us?  We would very much like to correspond with anyone who has a Tall Coton de Tulear, whether that Coton has been neutered or not.  We need as much information as possible about these fascinating Cotons.  You can contact us here.

 

A Few Interesting Points Reconsidered

A few additional terms are in order.  A genotype that contains both the same alleles, e.g., HH or hh, is called homozygous.  A genotype that contains two different alleles, e.g., Hh, is called heterozygous.  A recessive allele can only hide in a heterozygous state.  If a recessive allele is homozygous, then it is expressed in the phenotype, i.e., its product is visible for all to see.  A dominant allele can never hide.  Its product is always visible.  Therefore, a breeder can readily fix a dominant allele in his or her bloodline, but may have considerable difficulty eliminating an undesirable recessive allele.

Before we leave this short primer on genetics, let's summarize the preceding illustration one more time.  Suppose that in the preceding mating, three of the puppies were of normal height and one was very short.  What might you infer about the genotypes?  The simplest hypotheses would be:

  • Allele H produces normal height dogs and allele h produces short dogs.
  • Allele H is dominant over the recessive allele h.  But note: if the genotype HH actually produces a shorter than expected Coton phenotype, then H and h are codominant, each expressing themselves independently, but their products are canceled out in the heterozygote, (Hh, which is "normal height").
  • The genotype HH or Hh, (which is often shown as "H-"), will produce a normal height phenotype.
  • Only the genotype hh can produce the short phenotype.

Note that in the scenario presented here, three puppies had the dominant phenotype H-, but two of those three puppies were "carrying" the recessive h-allele.  That is, two puppies had the Hh genotype where the recessive h-allele was not expressed.  These two puppies are capable of passing on the h-allele to future litters, even though they themselves show no outward signs of having the h-allele.  Often, this is how, after many generations, a trait that was presumed lost or eliminated can suddenly reappear in a breed.

In codominance, a litter with homozygous and heterozygous genotypes may appear to exhibit a blend of phenotypes.  For example if the genotype HH is tall, and the genotype hh is short, then the codominant genotype Hh will appear to produce an intermediate phenotype between the two height extremes.  Note, however, that though the phenotype appears intermediate, the genotype is still discrete.  Alleles do not mix together like soup.  At no point do alleles H or h blend together and lose their heredity qualities.[3]

 

FOOTNOTES:

[1] This essay on Tall Cotons appeared originally in the Coton de Tulear News, Volume 9, Number 4, Fall, 1997, pp. 18-21. It has been modified for inclusion here.

[2] Alika Cotons, ("Alika" is Malagasy for "dogs"),  is the breeding program maintained by the authors of this book.

[3] Therefore, the allele "H" will remain intact as will the allele "h" in the newly combined genotype "Hh".  An "Hh" individual will still produce sex cells [gametes] with "H" alleles and other sex cells with "h" alleles.

---- End of Excerpt from THE Book ----