Bicolor? - Page 4

Hey Karen,
did you switch breeds on me? Your avatar is << gasp>> an Aussie Cattle Dog? But a very nice one I might say, lol!

I did Chris LOL well they say a change is as good as a rest... and boy do I need a rest LOL I've got 2 of the little darlings!! ;)

Association of an Agouti allele with fawn or sable coat color in domestic dogs
page 10:  The aw and at alleles. We found no difference in
Agouti exon 4 sequences between dogs carrying the
aw and at and alleles (Table 2) nor in the coding sequence
of a wolf or Gordon Setter. By analogy to
black-and-tan (at) in laboratory mice, it seems most
likely that at in dogs represents a regulatory alteration
that inactivates expression of hair cycle-specific
Agouti mRNA isoforms present in an ancestral
aw allele.
 

Also note on the same page, figure 3 of the "bicolor" shetland sheep dog with no toe marks.  It would seem inappropriate to me to call a black and white dog a "tan point".  Are dobermans with toemarks bicolor, and the remainder with no toe marks tanpoint?  It's all seems like semantics to me, and not an accurate reflection of the gene interaction that's taking place.

The comments I posted that were deleted by the mod consisted of good and relevant information not even about molly, that other readers might like to know.  She can describe her non-factual BS, and I can't post professional geneological findings that I can cite sources for?!  I've even conducted multiple breedings that back those theories.

Bi colour means 2 colours - doesn't matter if that dog is black and white black and tan or black and purple, it's still 2 colours and therefor Bi coloured. 
We use the term bi colour to describe a specific coat pattern in the GSD breed when really it's a Tan pointed dog,

A tan point can have pencil markings or it may not, so there has to be a modifier for the toe pencilling but what is it and where is it?

what is it and where is it?

Perhaps it's not to be "found" in a location per se, but instead primarily due to the interaction between two gene loci which have been extensively studied for responsibility for many phenotypes among many breeds.

The modifier is what makes a bicolor dog a bicolor and not a black/tan.  They are, in my opinion and experience, two different color patterns with two different genetic inheritability factors.  Bicolor dogs cannot produce black/tan dogs of any pattern (ie no black toe marks/tarheels and color pattern of bicolor) on their own (without being bred to a dog that produces black/tan).  However bicolor can be carried as a recessive to dominant colors (sable for instance).  My question would be, can a dog produce both black/tan and bicolor dogs from the same color gene (black/tan that carries a bicolor "gene tag" or whatever you want to call it)?  I'm not sure about that -

I've bred a dark black/tan dog (predominantly black) with black recessive, to a sable dog who carried bicolor recessive (known to produce bicolor dogs), and produced dark black/tans and bicolor (and sable) dogs.  A very dark black/tan who closely resembles OP's dog - to a sable dog with black recessive - black/tan pups from this match ended up dark black/tan even though they certainly appeared bicolor as puppies...Bicolor dogs to black, producing blacks and bicolors - I own a bicolor/bicolor female who produces bicolors, no black/tans unless bred to a dog who carries black/tan.  No blacks as she does not carry black (so toe marks and tar heels on a bicolor dog does not necessarily indicate black recessive).  Black/tan dogs can carry black recessive - no toemarks/tarheels to indicate black recessive or "bicolor gene".

It gets more complex.  I'd like to find out if a black/tan dog (no toemarks, tarheels) can produce a bicolor dog (toe marks, tarheels,, no tan markings @ ears or under chest) when bred to a black dog or other that does not carry black/tan gene.  If it can't, and I already know bicolor cannot produce black/tan directly (without being bred to a dog who carries black/tan) - then bicolor would obviously be a separate color to be considered in the GSD breed. 

And, we are talking about GSD here.  Other breeds have their own varying color pattern/markings and names for them.  Bicolor and Bi-Black Shelties are shelties - not GSD.  there are no solid black shelties, and there is no merle gene in GSD or blue eyes.. - cattle dogs are "every color under the rainbow" for gosh sakes - how could they be considered bicolor or anything close?  They also come in blue, red - never a "solid" color... different breed.  Black is a dominant color in some breeds, is recessive in GSD.  Doberman and Rott are 'bicolor" but don't use that term - and a sable GSD is certainly not the same as a sable collie or sheltie - and the term "sable" meaning black...  you can't compare GSD color/markings to a labrador and so on.

I'd like to continue this interesting conversation but keep it about GSDs please.

molly

Firstly let me say I'm not disagreeing with either of you, I'm just throwing my own hypotheses into the mix.

I haven't got time to get into this now and I want to read that paper that darylehret posted - but that will be later this evening.

The other thing I just wanted to say is no matter what breed of dog they all conform to basic pigment patterns, with the odd tweak or unique gene trait here and there.  Yes certain genes have been lost in various breeds because of selective breeding, 

Cattle dogs btw aren't all colours of the rainbow, they are basically a black and tan (In the case of a Blue heeler) dog with ticking gene. 
The Australian stumpy tailed cattle dog, has it's roots in the same genetic soup that spawned ACDs the solid gene in the breed went thataway with the ASTCD and the ACD 'lost' or it is extremeley rare the solid gene to become the dogs we see today.  (like brindle in the GSD)

And yep I want to carry this on, because it's got me all fascinated once again but on a broader scale, I don't think we can find the solution by just looking at the GSD, sometimes you have to get out of the box :)

My question would be, can a dog produce both black/tan and bicolor dogs from the same color gene (black/tan that carries a bicolor "gene tag" or whatever you want to call it)? I'm not sure about that -

If you accept the idea that black&tan and bicolor are each variants of the original wild type sable agouti with loss of function mutations, the rules of heredity that we are familiar with remain unchanged.  The bicolor remains recessive, and could not produce a black&tan phenotype without the help of the other parent.  The greater the loss of function on the agouti allele that's expressed, the greater influence we see from the MC1R gene, affecting overall phenotype.  I had a near-blanketed black&tan, who was recessive for an even more melanistic blanketed black&tan when her pups gained a black gene, which on the other hand caused lighter faded sable patterns through her sable mate.

The other thing I just wanted to say is no matter what breed of dog they all conform to basic pigment patterns, with the odd tweak or unique gene trait here and there.

I can agree with that, and this is sort of a supportive example.  A recent performed genome-wide association study of more than 1000 dogs from 80 domestic breeds have identified 3 genes that determine several phenotypes, influencing coat growth pattern, length, and curl. Point being, there isn't a "single" gene that determines each of these distinct phenotypes. Instead, theres a dynamic between them.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2897713/

Daryl

If you accept the idea that black&tan and bicolor are each variants of the original wild type sable agouti with loss of function mutations

I know we've gone over this many times... but again.. No, they're not two separate variants of the Agouti locus.  There is only one A locus allele that accounts for the wide range of expression of the tanpoint pattern, from the palest saddle to the darkest 'bicolour.'  This has been known for some time.  We are still waiting for the publication of the paper on the DNA research on this.

The greater the loss of function on the agouti allele that's expressed, the greater influence we see from the MC1R gene, affecting overall phenotype.

 MC1R is the E locus and this clearly has no influence in the expression of tanpoint pattern in the GSD.  We know this because the vast majority of GSDs are homozygous for this gene (E^m E^m), yet still there is a wide phenotype which follows a path of continuous variation, far greater than would be possibly from the influence of just one locus with four alleles, even if the others did occur with greater frequency in the breed.

One poster (Ambii I think?) has mentioned  facial masking  modifiers as possible candidates for influence in eumelanin shading on the body, and I'm in full agreement with this.  There's obviously much more to it than just one or two genes.

I'm in disagreement with you on both points, on behalf of studies that directly support my statements in that, 1) the black&tan is a variant of the original wild type sable, due to loss of function mutation, and 2) E locus does affect the A locus in their competition for expression.

If these are for any reason considered wrong in the future, keep in mind these are not my claims or discoveries.  I don't make stuff up, but each statement does fit and support the current model of hereditary transfer between phenotypes in my experience.

On another note, the breeding I mentioned above produced pups of this appearance below.
The sire on the top left is a sable with black recessive, and the dam would produce her color or very melanistic black&tans when given his black gene, but affected his sable gene with lighter/faded shades.