Sunday, June 19, 2011

Double Dapples - The Genetic Risk

continued from Double Dapples - The Genetic Risk 
by BloodhoundNdots at Anipal Times

I would like to express my thanks and gratitude to  Lisa J. Emerson for taking time from her busy schedule to write this article for me. I hope that anyone interested in dachshunds will purchase her book and learn about the coat genetics. Lets end the countless number of special needs dachshunds in the world by understanding the risks of breeding certain coat patterns.


Below is the article submitted to me by Lisa J Emerson author of The Wienepedia:  Dachshund Coats, Colors, & Patterns

Dapples, partis, and mixes – oh my!
by Lisa J. Emerson

You may have heard a breeder claim “Single dapples can’t have problems.” or “I breed for pie dapples because double dapples are a no-no!”  There are many myths out there when it comes to dog coat colors and patterns, and there will always be disreputable breeders who try to capitalize on them.

Dappling, called merle in most other dog breeds, is a pattern that causes dilution of color in varied, blotchy amounts on a dog’s coat.  Double dappling occurs when a dapple allele from both parents gets passed to a puppy; double dapple is created by two copies of the dapple allele causing a “double dose” of dappling, so to speak, on the body.  Many of the areas that would have simply looked diluted on a regular dapple turn lighter and white on a double dapple.

If you have heard that double dapples can have sight and hearing issues – even to the point of being blind, lacking eyes, and/or being deaf – this is absolutely true.  Those not cursed with such major deformities usually have minor ones that can be easily detected by the breeder doing proper testing on her dogs.

Can basically healthy double dapples be created?  Absolutely.  But breeding for double dapples is a feat rarely taken on by responsible breeders because of the honest work involved.  A buyer should be extremely nervous and run away if a breeder is not doing hearing and sight testing on double dapple parents and puppies before she sells them.  (The only reasonable exception to this is a breeder who has been breeding many, many generations who has already been diligent about weeding out problems.)  A breeder should know and be responsible for what they are producing.  The problem we have nowadays is that so few who do breed double dapples know what they are doing or care, especially when they can still make enough money from the “cute” or “I feel sorry for it” factors to get by, come up with a profit, and keep breeding more.  It is up to the buyer to avoid such breeders; only the market can change bad selling practices.

What is not commonly known is that single dapples can have the very same problems.  The incidence is lower, and the problems are often not quite as noticeable, but they still should not be discounted.

How can one tell single dapples apart from double dapples?  To be entirely honest, there’s not a 100% tried and true method, apart from genetic testing, that is applicable to every dapply-looking dog out there, but many observational generalizations can be made:

  • If there is noticeable sight or hearing defects, chances are generally higher the dog is a double dapple rather than a single.  Complication:  There are multiple genetic factors, not just dappling, that can be responsible for such defects.
  • If both eyes are fully blue, chances are generally higher the dog is a double dapple rather than a single.  Complication:  There are single dapples out there with two blue eyes, and there are plenty of doubles who have little if any blue in their eyes.
  • If there’s more than a little bit of white on the dog, and if the white meets the colored areas in a jagged way rather than a smooth way, chances are generally higher the dog is a double dapple.  Complication:  Random white areas called mismarks, usually found on the extremeties (face, feet, chest, and/or tail) can cause white on a dog of any pattern. Complication:  There is a whitening factor that can cause white on single dapples.  Further complication:  Parti-coloration causes white on the coat too.

Parti-color, which is on a different gene and a different chromosome altogether, is believed to consist of at least two different, more-or-less recessive patterns.  Traditionally, three parti-color patterns have been acknowledged:  tuxedo, piebald, and extreme white, all of which appear to occur in dachshunds.
  • Tuxedo is the pattern of most collies and basenjis.  A tux’s coat is between roughly 0% to 25% white.  Usually, but certainly not always, the dog has a well-demarcated white chest, partial or full white collar, white feet, white tail tip, and occasionally a white spot or line on the head.
  • Piebald is the pattern of many basset hounds.  A pie’s coat is roughly 50% colored and 50% white.  Usually, but certainly not always, the dog has a white chest, four white legs, white underbody, and white tail tip, among possible white on other areas.
  • Extreme white is the pattern of white bull terriers and white boxers.  An exwhite is between roughly 75% to 100% white, often with just part of the face, part of the ear(s), and/or an area usually near the base of the tail well-demarcated with color.

It has been supposed that these three parti patterns can be mixed on any given dog; for instance, a dog could be half tux and half pie, or half exwhite and half pie.  What is important to understand overall is that, in comparison to double dappling, the colored areas on any variety of parti-colored dogs are generally well-demarcated; that is, there is a more or less “smooth” edge to the color rather than the typical jaggedness seen on most double dapples.

It is a common myth that such-and-such parti pattern must look symmetrical, or that it must have four white feet, or that it must have a white tail tip, etc., or that a double dapple must have the same placement of white or that it must be completely asymmetrical.  The truth is, every dog is an individual, and where that individual’s particular pigment cells migrate or fail to migrate to on its body cannot be proficiently predicted.

Parti-coloring is, at least in dachshunds, often somewhat symmetrical on the head, meaning the colored areas that are on the head (if any) often match – if one side of the forehead has color on it, usually the other side of the forehead does too.  But then, there are numerous counter examples to this.  Double dapples are usually more irregular, but they can have coloration in the same basic places as parti-colors can too.

As I have pointed out in my book, the white from parti-coloring can affect the hearing status of a dog in the same way that white from double dappling can.  There is next to no data on this in the dachshund breed, and breeders of parti-colors should be responsible by testing their dogs’ hearing and publishing the results.  The good news is, parti-coloring does not cause sight impairment or blindness in dachshunds, although this fact should not preclude responsible breeders from sight-testing their dogs for general purposes.

There is one factor that seemingly affects parti-colors but not double dapples:  ticking (and roaning).  This is where spots (or blotches) of color can develop over a few weeks’ time on the white areas of the parti-colored dog’s body.  These spots do not occur outside of the extremities (muzzle, ears, and feet/legs) on double dapples.  Not all parti-colors have ticking or roaning, though – many are just as snowy white as the white on double dapples.


Phenotypics:
dapples
parti
colors
double
dapples
usually has white on the extremities
(muzzle, chest/underside, feet, &/or tailtip)
X
X
can have blue eyes if over approx. 3 months old *
X
can have ticking or roaning over the whole body
X

usually the colored/white edges are smooth
X

can be deaf or hearing-impaired

due to the pattern
X
X
can be blind or sight-impaired

due to the pattern

X
(* There are breeds, such as huskies, border collies, and dalmatians, where one or two eyes can be blue and the dog not be dappled.  If a non-dapple cause of blue in the eyes does occur in dachshunds, it is uncommon to very rare.)

To thoroughly muddy the waters and make your head spin if it isn’t already from all the confounding variables and possibilities, there are dachshund breeders who are careless and mix the dapple and parti-color patterns together.  Very often they do not even they know what patterns their parent dogs are let along what their resulting puppies end up being.  This is a dangerous practice, not only because of not being able to easily parse the visuals, but also because dappling can “hide” on the white of the parti-color patterns, thus leaving the breeder not knowing that her parti is also potentially a dapple, and if she should mate it to another dapple, double dapples could of course easily result – even worse, double dapple parti-colors could result!

In breeds like australian shepherds, most of whom are tuxedo and many of whom are dapple as well, “surprizes” of tuxedo double dapple puppies occur frequently enough.  Often the cause is that dappling doesn’t happen to show up on any of the colored areas of the body, and the larger the area of white on the body, the greater chance a dog with very little dappling on it can “hide” the dappling in the white.

A dapple parti-color will have white areas just like a plain parti-color.  The colored, non-parti-colored spots may have full color like a regular parti (and dapple can be hiding in the white), or they may have noticeable dappling on them.  It is possible for the dappling to make the edges of the colored spots look almost jagged, more so than they would normally, giving the impression the dog might be a double dapple instead of a dapple parti.

Now go a step further and imagine the scenario for a double dapple parti-color:  Visualizing any clean parti-colored spots is impossible because of all the white and jagged edges of the double dappling – assuming there is any color in order to have an edge to it at all.


Genetics:

mm SS normal = non-dapple, non-parti-color
Mm SS = dapple
MM SS = double dapple (no obvious ticking beyond the extremities)
mm Ss = normal that carries a parti-color (if carrying pie or exwhite, may appear somewhat parti-colored)
Mm Ss = dapple that carries a parti-color (if carrying pie or exwhite, may appear somewhat parti-colored)
MM Ss = double dapple that carries a parti-color (if any color is on it after the double dappling is through, can be even whiter if showing any parti; probably no obvious ticking beyond the extremities)
mm ss = parti-color
Mm ss = dapple parti-color (assuming any dappling is visible, the edges often won't look as clean as they should)
MM ss = double dapple parti-color (good luck telling this apart from an exwhite or from a double dapple!; probably no obvious ticking beyond the extremities)

Given the evidence where these two genes are involved, it can be said that responsible breeding practices are those in which dappling and parti-coloring (at least, pie and exwhite) are kept separate in a breeding program.  Or, even better, the breeding program only keep dappling or keep parti-coloring (or neither, if the breeder so chooses) going; if dapples are chosen, they at least get sight-tested, and if partis are chosen, they at least get hearing-tested.  If double dapples are pursued, there is testing of both kinds.  Pedigrees should be kept and updated, as well as fact-checked, by the conscientious breeder to allow for the greatest accuracy in determining what she has.  Frequently inaccurate pedigrees produced by registry organizations alone in no way pass muster.

Again, in the end, it is up to the buyers’ pocketbook to control what is produced by breeders, and the dogs are counting on us to pick breeding practices that come across as sensible and avoid breeders who don’t come across as particularly accountable.  If there is obvious white on coats and no hard proof of current (or past) testing to back it up, consider looking elsewhere for a breeder who can show you with authentic, scientific data that she has a good idea of what she is doing.  Don’t take “My dogs don’t have problems.” or “He can hear/see something, so I /my vet/my hairdresser says his hearing/sight is perfect.” as an answer!

1 comment:

Hound Girl said...

Holy Cow,I just learned alot from this article. wow.