
Eek! I know what I
want to say / explain regarding coat colours, but I'm not very good at putting it into words I'm afraid!
Essentially, I'm pretty sure it is genetically impossible to have a solid blue SBT without brindling; the blue coat colour is a dilution of the black / brindle gene.
Similarly it is genetically impossible for a solid black SBT to be produced without brindling.
ETA, I've just noticed James, you've also mentioned that the pup is produced from blue sire to blue / brindle dam, therefore by my reckoning, pup is more likely to be fawn in colour, i.e. even more dilution occurring.
Have a little read of this website, very useful info regarding the genetics behind coat colouring.
http://abnormality.purpleflowers.net/genetics/brindle.htm - brindling explained.
http://abnormality.purpleflowers.net/genetics/dilutes.htm - dilution explained.
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Courtesy of another website, explains it so much better than I ever could!
1) Genes come in pairs. For every trait needed to make a dog, a puppy gets one gene from its sire, and one from its dam. It is the combination of these two genes acting on each other that gives us the dog that we see, as well as the genetic structure of the dog that we don't see.
2) When breeding two animals of the same recessive color or pattern, more dominant colors or patterns will NOT be seen in the resulting litter.
3) All dogs are genetically either red or black. All other colors are a genetic variation on these two base colors. Black is dominant to red. So if a puppy receives one red gene and one black gene, it will be born as a black dog. If it has two red genes, it will be red. And of course two black genes still result in black. A red dog has nothing to give its offspring but a red gene. So if it is bred to another red dog, all puppies will be red. A red dog can produce black puppies if bred to a black dog. A homozygous black dog (meaning that it has two black genes) can only produce black puppies. It has only black to give, and black will dominate over any red genes combined with it.
There is a dilution gene, which changes red to varying shades of blue fawn, and also changes black to blue. Full expression of red or black is dominant to the dilute. So it takes a dilute gene from both parents to produce a dilute puppy. Two dilute colored dogs cannot produce a puppy with full expression of color. It is important to note that not all fawns are blue fawns, as non-diluted red can be expressed from deep red to a pale fawn, but the nose and eye rim pigment will be black. On a blue fawn, nose and other skin pigment will be blue.
There is another less common dilution gene, (liver dilute) which changes black to liver (a dark chocolate color, as seen in Labrador retrievers), and red to liver red (which can exist in a range of shades). In both forms of liver dilution, skin pigmentation will be liver as well.
Brindle is a pattern overlay on top of the base coat of the dog. Any dog with a visible brindle pattern, is a red dog. A black brindle is genetically just as much a red dog as a brindle with only the faintest brindle markings. The brindling is simply heavier on the black brindle.
Brindle is a dominant trait. At least one parent must carry brindle in order to produce brindle puppies. Two non-brindle red dogs cannot produce a brindle puppy. A black dog can carry a brindle gene, but you won't know it unless it also carries a red gene and is able to produce red puppies, which may or may not be born brindle. Basically you can't see black stripes on a black dog, although I've been told that in the right sunlight you can sometimes see faintly darker blue stripes on a blue dog if it carries a brindle gene.
Any puppy produced by a dog that is homozygous for brindle (2 brindle genes), will be visibly brindle if a red pup, and carry brindle if a black pup. A black or blue pup, which carries a brindle gene, is sometimes called a masked brindle (meaning the brindle pattern is masked or hidden under the black color.) This should not be confused with the term "masked brindle" which refers to the black mask sometimes seen on the muzzle of visible brindles and non-brindle red dogs.
Black masks and sabling on red dogs are also overlays of color on the base coat, but are independent of the brindle gene and each other. Now, if you add the dilute gene (actually 2) to a red dog with a brindle overlay, you will get what is called a blue brindle. It is still a red dog, but the dilute gene dilutes the black brindling to blue, and the red base to fawn and skin pigment to blue. A blue fawn is a red dog sometimes with black masking and/or sabling but with diluted red base, diluted masking/sabling, and diluted pigment.