Mantle Coat Colour Genetics
Mantle Danes can come in one of two genotypes. They are either irish homozygotes or piebald heterozygotes. Irish homozygotes will "breed true" (as the expression goes) for the Mantle pattern, because these dogs have two copies of the gene that produces what is traditionally called "Irish markings" that we associated with white trim (tuxedo markings). This genetic pattern unfortunately does not completely match up with the current written AKC standard for the Mantle Dane, but does follow the general tradition for "harlequin black" that is generally preserved in the FCI standard (with the exclusion of the recently added Plattenhund). In other words, Irish pattern produces a partial-collared to full-collared sort of Mantle dog, a dog that will always have white on the muzzle, have socks or stockings, belly and/or chest white, and a dog that will never have a break in the blanket, or in any way have the white "creeping into" the body markings. This is the true Irish dog under CC Little's old system. The piebald heterozygote is CC Little's "pseudo-Irish" dog. Both genotypes produce the Mantle phenotype. But the key here is they will breed very differently. That hasn't been well understood to date by most Dane breeders.
Another difference here from what most breeders were taught, and is newly discovered, is that the Irish pattern is NOT produced by the same gene that produces piebald (Der Plattenhund). Piebald turns out to be the simple (& single!) recessive at the "S" locus. The dominant homozygote is a solid black (self-colored) dog: <SS>. The recessive homozygote is a piebald--Der Plattenhund: <s^p/s^p>. The hybrid that results from a dog being heterozygote here is a recongizable sort of Mantle typically--but Little's "pseudo-Irish" dog: <Ss^p>, so will breed differently from the "true" Irish dog. Now it is the case, in introducing the piebald gene into various gene combinations, some of the resulting hybrid (heterozygote) puppies can range from what some might called "mismarked" black or mantle to Mantles with a broken blanket. This range depends partially on other factors unrelated to the S locus (mostly if the dogs in question carry Irish genes as well), but also results from the piebald gene simply being unstable. Typically in a litter where piebald is present you WILL get a wide, wide range of markings: from nearly solid puppies to nearly white puppies. This is because the piebald hybrid parents set of genes that make them appear as Mantle-marked split in the offspring, recreating the black-to-piebald range their parents came from.
In contrast, if the breeder concentrates on producing Mantles who are Irish homozygotes, the range of markings is going to be much narrower & more stable in pattern: all the puppies can be expected to have some kind of recognizable Mantle markings: white on their extremities (legs, tail, muzzle), and all the puppies will have solid blankets and good head markings. In other words, Irish homozygotes breed true & the resulting litters will have puppies who only range from having partial collars to full collars. No solid (or mismarked) blacks or piebalds will be born to matings where both parents are Irish homozygotes and free of the piebald gene. The Irish allele (gene) is NOT on the same locus (gene location) at piebald; it is NOT at the S locus, but on another chromosome entirely, so sorts independently--is inherited seperately from piebald and as a distinct trait a breeder can focus on concentrating in their bloodline. Very little in Harlequin breeding offers this sort of control, so it's a valuable point of pattern managment to be able to establish homozygosity of this gene. Here a dog can have one, none, or TWO of the gene. Those dogs with zero Irish genes will be solid black, those with one mostly will appear as mismarked blacks (in the absence of the piebald gene); those with two will always display a Mantle pattern.
Although many pseudo-Irish Mantles lack Irish genes entirely (because these recessive white genes are cumulative, meaning they all add white markings to the dog, so then the dogs become too white to be called true Mantles at some point), there are some dogs will have one copy of the Irish gene as well as one copy of the piebald gene and appear as flashy Mantles. And there are some dogs without anything but one copy of the piebald gene that can end up being defined as mismarked Black/Mantle. This gene is just very unstable in the markings it produces. Piebald heterozygote Mantles will typically have flashier markings than their Irish Mantle counterparts, but the markings will also tend to have certain tell-tale traits:
- A break in the blanket is a dead give-away the Mantle is a piebald hybrid, not a true Irish Mantle,
- Asymmetrical markings are a characteristic of the piebald gene, and in contrast the Irish gene produces stable, symmetical markings--so dogs with socks on one side, high stockings on the other, dogs with odd & assymetrical markings are likely piebald hybrids,
- Creeping white into the body proper is a trait of piebaldism; this is the attempt of this gene to break the body up into the spots, or "plates" of color that are characteristic of this gene in its fully realized form. So dogs where there is a strong line in the flank creeping upward, where the collar becomes a large shawl, where the blanket (mantle) on the body doesn't reach down toward the belly, where the head markings are completely split into two black areas over eyes/ears (i.e. the "cap" is lost) are all traits characteristic of the piebald gene.