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by pod on 15 February 2011 - 14:02
Please could you answer my questions IN YOUR OWN WORDS.
Are you suggestion that the interaction between these two genes accounts for the wide phenotypic expression between the palest saddle and the darkest bicolour?
If so, I'd be interested to hear, in your own words, how you think this is possible without allelic variation in these two loci. Or are you suggesting there is allelic variation?
by eichenluft on 15 February 2011 - 14:02
jaggirl - it's really pretty simple - if the sire is in fact genetically bicolor, then he will produce bicolors. If he is genetically black with bleeding, then he will produce black with bleeding (and NOT bicolors, if bred to a black female as your pups' dam is). He looks black to me as does your pup and her littermates. If his toes/vent is tan, I suspect the color is not "clear" as it would be with a bicolor - so it would be bleeding. And, even if Czech doesn't recognize bicolor as a color - dogs in Germany that are bicolor (also not recognized there) are registered as black/brown - not black.
Still curious to see the results of the genetic test, but now knowing it is an all-breed test, not sure if the results will be conclusive for GSDs but interested to find out. I think the real test would be to breed your dog to a black dog and see if there are any bicolors produced.
by jaggirl47 on 15 February 2011 - 15:02
It was always assumed that it was just bleed thru on all of them. However, if you saw my pup in person (pics do not show well at all) you would say my pup is a melanistic bi. That's why I am doing the tests.
My pup's grand-dam (sire's dam) is a blanket black and tan but has produced bi colors. I have done ALOT of searches for her lines.
I really am interested to see what the genetics show for her.
by eichenluft on 15 February 2011 - 15:02
Here are two gentically black dogs with a LOT of bleed-through. They started "bleeding" at fairly young ages - not much noticed before 1 year old though, and no tan vent at birth - they are black, 1/2 siblings - dam is bicolor, sire is black. Now they would appear bicolor, yes? But they are not. The one sitting is darker, but has a lot of bleeding behind his legs.
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by pod on 15 February 2011 - 15:02
If this is so, it's not going to tell us much in reality. A hasn't been completely sequenced yet, or at least it hasn't been published, so A locus cannot yet differentiate between 'sable' and tanpoint, but obviously this should be evident from phenotype. There is no A locus differentiation between saddle, blanket and bicolour, (these are all at tanpoint), but there is between tanpoint and recessive black so all we can determine is if this dog is recessive black or a carrier of it.
So if this is a tanpoint carrying rec black, it will be designated ax a (ax is the temporary symbol given for 'sable/tanpoint until this research is complete). If he is recessive black it will be - aa
E locus. If this is a normally pigmented GSD with mask he will mostly likely be homozygous Em Em. If not homozygous, then possibly a carrier of 'white' Em e, or a carrier of no-mask Em E.
K locus. Most likely is Ky Ky but can't rule out dominant black K altogether as this could possibly be in the GSD genepool.
by jaggirl47 on 15 February 2011 - 15:02
As far as the testing, the a allele has been sequenced, just not the at. If she shows to be something other than a a+a but does not fall into a+aw (black ressesive sable) or a+as(black ressesive saddle), then she is a+at (black ressesive bi) with a (black) being the ressesive color.
Confused yet? lol
by darylehret on 15 February 2011 - 16:02
Pod, there are many causes and interactions that interplay in how we observe differences between same-type alleles, so that could require a rephrasing of the question. None of it's truly simple, but if the rules for hereditary transfer can be described, and with simplicity, then I will be personally satisfied.
1) Histones permanently activate or deactivate gene expression via a process known as "DNA methylation." These small chemical groups within the cells latch on to areas along the dna strand and result in changes that can be passed hereditarily for generations, without any alteration to the dna structure.
2) "Besides Agouti and Mc1r, mutations in at least 10 additional genes can interfere with the switching of pigment type." Agouti remains central though, in our breed, because of rules of dominance and the phenotypic output of offspring. i.e., a bicolor can't be responsible for b&t phenotype, and a single breeding could not produce all four general phenotypes; sable, b&t, bicolor, black
3) "linked" genes, that are continually passed together, because of general close proximity on the chromosome between usual breaking points
4) already mentioned, the various grades of LOF between sable to black in agouti function. Agouti and E-locus are the "major players", but the LOF between the various allelic types that we recognize aren't necessarily "identical" to each other. As already stated one sable gene from one family can be distinct from a sable gene of another family, in regards to the degree that LOF mutations have affected them.
This is all further complicated by the uncertain mechanisms of pigment switching between the two genes, A and E. If you're interested in some more "deep reading" there is The pigmentary system: physiology and pathophysiology, which I've bookmarked under the chapter involving pigment switching.
"Are you suggestion that the interaction between these two genes accounts for the wide phenotypic expression between the palest saddle and the darkest bicolour?"
Somewhat, primarily I suppose. Of course other alleles affect overall appearance, we can't ignore the phenotypic differences that involve the K locus and others.
by pod on 15 February 2011 - 17:02
Daryl, you're quoting again, but do we have a little eureka moment here?
2) "Besides Agouti and Mc1r, mutations in at least 10 additional genes can interfere with the switching of pigment type."
http://www.hhmi.org/research/investigators/barsh.html
But then you indicate that still don't grasp this, by saying - Agouti remains central though, in our breed, because of rules of dominance and the phenotypic output of offspring. i.e., a bicolor can't be responsible for b&t phenotype, and a single breeding could not produce all four general phenotypes; sable, b&t, bicolor, black
TANPOINT is responsible not bicolour. Bicolour is just one expression of the tanpoint A locus allele. There is already disagreement over what defines bicolour and given that modifying genes can work in order of dominance too, there should be no argument over this. Besides, the A locus is not in question. It has already been sequenced (yet to be published) and the alleles designated Ay aw at a. Note there is no as saddle allele.
"already mentioned, the various grades of LOF between sable to black in agouti function. Agouti and E-locus are the "major players", but the LOF between the various allelic types that we recognize aren't necessarily "identical" to each other. As already stated one sable gene from one family can be distinct from a sable gene of another family, in regards to the degree that LOF mutations have affected them. "
All I can say Daryl is that you haven't understood my previous comments on this. You seem now to have recognised the existence of modifiers, can you now see that they can play a role in defining the difference in pigment distribution between two shepherds that are identical on the A & E loci ie. they are at at Em Em, yet one is a pale saddle and the other a dark bicolour. Now the A and E loci can't be responsible for this because they are identical in both ie. they have the same codons, the exact same nucleotide sequence, so will code for the exact same proteins.
There has to be some other genetic variation that accounts for the difference in pigment shading. This where your "at least 10 additional genes" come into play by providing the variation that codes for different switching between eumelanin and phaeomelanin pigments, to facilitate lightening and darkening. Edit added - The same modifiers contribute no doubt, to the the varying shade differences in sables and blacks
Somewhat, primarily I suppose. Of course other alleles affect overall appearance, we can't ignore the phenotypic differences that involve the K locus and others.
Other genes yes, but not the K locus, for the exact same reason as I have outlined for E locus. Shepherds are probably all homozygous Ky Ky for this gene. There is no variation here that could contribute to the pigment balance in the GSD. Now if we were talking about Dutch Shepherds, or Labradors, or Great Danes, then yes, K would contribute, but not in the German Shepherd. Must add a note here to say that dominant black and brindle could possibly occur at a very low frequency, but brindle particularly unlikely.
by darylehret on 15 February 2011 - 20:02
TANPOINT is responsible not bicolour. Bicolour is just one expression of the tanpoint A locus allele.
Huh?? Tanpoint is just one expression of the sable A locus allele.
Now the A and E loci can't be responsible for this because they are identical in both ie. they have the same codons, the exact same nucleotide sequence, so will code for the exact same proteins.
I think I'm on a totally different planet now.
There has to be some other genetic variation that accounts for the difference in pigment shading.
Right, but it sounds like you're assuming it comes from another loci, which for the reasons I've stated (in #2) is very unlikely; the model for rules of inheritance are stable, the A-locus plays a central role in the expression of the "bicolor" phenotype. You can (in theory) assign it to any other loci, but not without completly altering the model for the rules of inheritance and order of domincance, which to this point have held true in actual breeding experience. If it were controlled from another loci, then a bicolor would be able to produce a black&tan, and also, a paired breeding could produce more than three of the basic four phenotypes.
by pod on 15 February 2011 - 20:02
No no no NO! Daryl, do we need to start with the very basics? I can now see why there is so much confusion.
A locus is a gene, not an allele. Do you know the difference?
A locus is the Agouti complex of alleles, not just sable. Sable is just one allele of this gene.
Edit - Ok, I've re-read and may have misunderstood some of your statement, sorry.
But, tanpoint is a separate allele from sable. It has a wide expression from lightest saddle to darkest bicolour. There is no question over this, the researchers have confirmed it.
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