The Genetic Throw Back.

DesO'Neile · The Genetic Throw Back.

There is a thread in this section discussing the parentage of what the owner's said was a "Chocolate” Weimaraner. There has also recently been a discussion about "Blue" variations of the same breed. I find it interesting that some people are prepared to make categoric statements to the effect that you simply can’t produce a chocolate Weimaraner form pure-bred stock. I am not wishing to reopen these particular discussions but having seen two genetic throw backs, a Gordon Setter and an Irish Red Setter, and since most breeds were at some time an amalgamation of other breeds is the theory of the genetic throw back now dead.
I have posted a picture of Bob Trueman’s Champion Stake winner Freebirch Vincent. This was more often the colour of Gordon Setters before the fourth Duke (?) plumped for the now familiar Black and Tan coloration. (Bob currently owns at least one “Red” Gordon)

tashap

Mike

Des,
As I understand things the idea of something being a genetic throwback is dead and buried, it tended to be trotted out as an excuse by someone who hadn't been keeping an eye on a bitch in heat. That doesn't mean that unexpected things can't happen sometimes but I'll come to that in a bit.

Some aspects of genetic inheritance are well understood and some aspects are quiet easy to explain. Needless to say some aren't!

Apologies if I go over some ground you already know. Chromosomes are essentially DNA molecules. Chromosomes come in pairs, one from mum and the other from dad. Codes for specific proteins (these protein will code for characteristics like coat colour) are always found in the same place on a chromosome, this place is the locus (or loci plural) Alleles code for different variations of proteins at each locus. Each allele will be one of a pair (one inherited from mum the other from dad).

Putting things simply alleles can be dominant, recessive or neither. The important thing to remember with coat colour is that you will only see a recessive trait if both the alleles are coded for it.

Dealing specifically with the mode of inheritance in Weims (i.e. the whole blue vs. grey argument)

If you think of Weim as having two loci that control coat colour, b and d.
The b locus controls Black / brown (Black is dominant to brown) and the d controls dilution (D undiluted d diluted). Diluted Black is blue and diluted Brown is grey.

Fundamentally the grey Weimaraner is homozygous for both colour and dilution, that is to say it is bb dd. Because the grey Weimaraner is homozygous for both alleles, a grey Weim x grey Weim mating can only produce offspring with the coding for dilute brown (i.e. bb dd)

The blue Weim however can be either of the following codes BBdd, Bbdd. A blue Weim is still fundamentally homozygous for dilution (dd) otherwise it would be black not blue. The blue Weim can either be homozygous for the blue colour (i.e. BB, not a grey carrier) or heterozygous (i.e. Bb is a grey carrier). Because black is dominant to brown it is possible for brown to stay hidden for generations amongst carriers and never be expressed until it meets another carrier. This is one of the areas where close matings and line breeding help to "fix" characteristics, with recessive characteristics that you can see (i.e. the colour of grey Weims) when you are homozygous (both alleles the same) and it allows you to breed true to type. It is much harder to breed to select dominant characteristics and be sure that you have got them homozygous (and fixed).

I think this is where your "genetic throwback" comes in Des. I don't know for sure but I would say it is likely that some of the black and tan dogs (which I suppose must be dominant) where carrying the recessive white gene and it unexpectedly pops up from time to time (even in purebreds) If you started to breed white to white (assuming it is a recessive characteristic) you wouldn't suddenly have black and tan dogs popping up as you would need two recessive alleles even to see the white, so a white x white mating will breed true to type.

Because the grey Weim is homozygous for two recessive traits (i.e. bb dd) it can be said that a) the blue Weim isn't a genetic throwback because the black gene is dominant to the brown so it couldn't "lurk" undetected for generations to suddenly appear, it would always be visible (it is also the reason why it is unlikely that a mother son mating would have produced the original blue, either the mother or son would have had to have been blue anyway! As the kennels that held these dogs also had dobes which are black dogs it would appear that it is much more likely to be an out cross.) b) because the grey is a recessive trait blues could be removed from the gene pool in one generation and wouldn't reappear again c) the chocolate Weim is in a similar position to the blue although the base colour is correct i.e. brown (bb) it is either heterozygous for the dilution (Dd) or homozygous (DD) again because the grey Weim is homozygous (dd) it can't produce the dominant dilution characteristic. So somewhere the dominant dilution factor has crept in, GSP / Lab who knows.

Their is also the possibility of genetic mutation, but I believe there are two reported early instances of blue weims separated by something like a ten year gap (might be muddled on this as it's in the memory but I can't find references to back it up!) The likelihood of the same random genetic mutation occurring within ten years of each other isn't very high especially when you consider other more likely explanations (i.e. unintended or even deliberate out cross at kennels which where known to also breed balck dogs)

So in summary Des, I guess you can have genetic throwbacks of sorts with dominant characteristics but you can't if they are homozygous recessive.

Hope that helps.

If you are interested in reading more about the inheritance of coat colour this website is useful:

http://skyway.usask.ca/~schmutz/dogcolors.html

tashap

The early blues if they are the ones from germany were both later admitted to have been a cross with a neighbours doberman. The area the weimaraner and doberman come from is the same. Dr Petri told an american whose dog he was judging that both dogs had come from this type of mating. So the Blue really is a doberman x weimaraner its just one was shipped off to america and bred from.

As a point of interest the early weimaraner registrations were kept with the established records of the german shorthaired pointer in a volume called the stammbuch kurzhaar. I have copies of some of these from 1900 - 30 the records were kept by region so they are not complete but this was standard practise.

DesO'Neile

Mike,
What you are saying is that the chocolate dog can't be a throw back because they can't happen in Weimaraners? But it might in other breeds.

Mike

That would have been a quicker way of putting it!

But fundamently it is possible to have throwbacks (for want of a better term) in dogs with dominant traits (i.e. the dominant trait is masking the recessive) but not in dogs which are displaying recessive traits (because by definition they will be homozygous for that recessive trait)

So in the example of the chocolate Weim it can't be a throwback.

Allyson

A bit like saying the long haired vizsla is a throwback! Wink

Long hair must be in there somewhere for it to appear.

There is and never has been any "chocolate" in the Weimaraner therefore it can and never will be chocolate.

Hound markings (dobie markings, ginger jobs) etc occasionally do appear as we know that the origins of the Weimaraner included dogs with this.

Someone I know has bred a Gordon which is not black and tan but liver and tan and is currently owned by someone who works on the KCAIT scheme.