Standard Accepted Coat Color Genetics in Dogs

Standard Accepted Coat Color Genetics in Dogs

with an Explanation of the alleles present in the Great Dane & Commentary on the Multiple Difficulties encountered when attempting to breed HARLEQUINS

COAT COLOR LOCI: (note the title is "standard, accepted" coat color genetics--various speculations or disputes may be noted, but are generally not addressed. The article, in any case, is specifically written for Dane fanciers):

LOCUS A: Pattern locus: allows for the distribution of dark (black or brown, i.e., eumelanin) pigment. Contains 3 (possibly 4 to 6) alleles with general dominance established.
A' = allows for a self colored dog; full body distribution of dark pigment. Also called As.
ay = restricts dark pigment distribution; produces fawn/sable.
aw = agouti "wild-type" allele: gives wolf-grey coloration. Also called ag.
at = tan point allele: gives bicolored animal; dark body with tan points.
as = gives dark saddle pattern on tan body.
(ab=recessive black said to be present in some breeds. This claim is often related to a further claim that dominant black is not actually located here, but this really isn't pertinent to Danes & in any case, is mere speculation at this juncture. For more on this topic, see Sue Bowling's site. The idea is basically that dominant black normally isn't seen in mammals at this Locus, coupled with a claim that recessive blacks seen are not modified atat dogs, but a true recessive allele all its own. Speculation is that true dominant black might be present at the top of the E Locus. The data so far are not conclusive for any theory. Again, pragmatically, the standard, accepted format presented above works for the Great Dane breed.)
Present in Great Danes: A' = all blacks, blues, Harles, merles, et al. carry 1-2.
ay = all fawns & brindles homozygous at this locus.

LOCUS B: Pigment Locus: allows for black & liver(chocolate/brown) dilution pigment.
Contains 2 alleles with simple dominance.
B = forms black pigment.
b = forms brown/liver/chocolate pigment.
Affects skin/hair color simultaneously.
Present in Great Danes: B = standard calls for dominant homozygosity. b = is present & carried recessively on occasion. Dogs who are bb must have brown (not black) noses, eyerims & pads. Reduction in eye (iris) color intensity/depth is noted. "Red" danes mentioned in early history/pedigrees/standards may have been bb "liver" red (called "rot"as opposed to fawn, which is called "gelb"). "Chocolate" danes have been noted. See Jane Chopson's article for more info on the topic, as well as the article on the Drapp Dane.

LOCUS C: Pigment locus; affects depth of red/yellow pigment.
Contains 3 (possibly 4 to 6) alleles.
C = allows for full depth of red/yellow pigment.
cch = reduces depth of pigment: produces washy or pale yellow coats.
cd = possible "dark-eyed/white-coat" allele.
ce = extreme dilution = creme-colored coats.
cb = "cornaz" coat with blue eyes
c(a) = true albino; total reduction of pigment via the interruption of the tyrosine pathway. Present in Great Danes: C = standard calls for homozygosity. cch = appears to be present in some fawns/brindles. "Washy" coat color may be explained by this locus.

LOCUS D: Pigment locus; produces dilution of black to slate/blue/grey/maltese pigment.
Affects skin/eye color simultaneously. Contains 2 alleles.
D = allows for black pigment to form.
d = produces blue/slate/grey dilution.
Present in Great Danes: D = all animals with black pigment. d = all blues/animals with blue markings/without black pigment are recessive homozygous at this locus. All dd have non-black nose, eye rims & pads. Reduction in eye (iris) color is noted. **bbdd-The Drapp-colored dane: This odd color, called "Isabella" or Doberman "fawn"
(i.e. Wiemaraner coat color-a mouse color), perhaps more properly referred to as dilute chocolate, blue-liver or double dilute, may account for the odd color referred to as "Drapp" in early discussions of the dane. The other likely explanation for this "drapp" ( a lilac color or cafe-au-lait brown with flesh-pink nose) is a chinchilla dilute blue--cchcchdd.

LOCUS E: Pattern Locus: restricts location of dark pigment.
Contains 4 alleles including superextension.
Em = gives dark mask.
E = allows for self colored dog/action of alleles of A Locus.
ebr = produces brindle pattern (if allowed; as with ayay homozygotic fawn/sable).
e = restricts pigment to red/yellow (no dark pigment can form).
Present in Great Danes: Em = produces masks on fawns/brindles;hetero-or homozygous .
E = all other Danes except /fawns/brindles, theoretically homozygous; "white-faced" fawns are EE. ebr = produces brindles; may be Em/ebr or ebr/ebr. e = some suggest ee fawns, as well as ayay fawns exist/existed in the breed. there are reported fawn to fawn breedings that have produced black pups.
There is a current trend to place masking at another locus; even brindling as well. But the appearance of brindling is common from ay & aw alleles & these are not genetic brindles (e.g. Afghan Hounds). There is no real evidence to necessarily amend the A & E Loci; it is reasonably argued that these claims come about from a confusion over the relationship of phenotype to genotype may be prompting claims for exceptions-see example given on brindling. Maskless (white-faced) fawns are seen especially in fawns from black to black breedings: which would confirm the placement of masking at the E Locus. Brindle danes also throw maskless fawns; also confirming the above explanation of the E Locus. In any case, since ee "fawn" Danes are rare to non-existant & brindles and masks both, in Danes, appear to breed by the standard, accepted coat color explanation offered here, there is no reason to complicate the above with these speculations (at this point). But please note, as Willis (1989) says: "The relationship between ay & e is uncertain." The same could be said (in some ways) of the relationship between A & E Loci.

LOCUS G: Pigment Locus: produces greying of dark pigment
Contains 2 alleles
G = dominant greying/paling allele
g = recessive/no paling of coat
Present in Great Dane: only recessive g allelle.

LOCUS M: Pattern/Pigment Locus: the so-called "merle" or "dominant white" locus which causes a reduction in allowed pigment. Pleiotrophic; it affects sensory organs/reproductive capabilities & is related to other such dominant white spotting loci common in mammals (e.g. Von Waardenburg's Syndrome). Produces a characteristic increase in white areas & areas of reduced pigment, with patches of mid-tone and full pigment when heterozygotic. Note it is considered both a pigment AND pattern locus; it is unique to the dog world in many ways. Commonly produces a more than 50% white animal when homozygotic with associated anomalies. Fetal death rate for MM dogs is 50%; surviving pups generally suffer sensory & other anomalies with hearing & sight defects most common. Produces dapples, blue & red merles; believed necessary to produce harlequins. (Note: i.e. if "Harlequins" are more than a phenotypic phenomena and not just a merle variety.) Considered to be a documented incomplete dominant. It is unknown if alterations in penetrance and/or modifiers affect phenotype. Wide variations in phenotype are noted in & between breeds. Only color coat gene in dogs in which there is little known about its action.
Contains 2 alleles.
M = merling/dappling/patching with increase in white/mid-tone areas.
m = non-merling allele.
Present in Great Danes: M & m. In harls/merles heterozygotic: Mm. MM homozygotes seen in some white & near-white dogs which are usually deaf/may have eye & reproductive anomalies/be sterile. Some (~50%) MM embryos may be non viable. May be difficult to distinguish, phenotypically, from spsp & swsw piebald dogs, as well as Mmsp- or Mmsw- merle (merlikin) and litely marked harl dogs. Some "merlikin" & harlequin dogs may be genetic white (homozygous) merles. The separation of harls & merles in the Great Dane may well be a phenotypic phenomena not genetically represented (Little, 1955). It is also possible (likely?) that independently inherited modifiers to the merle allele are what affects the range seen from harl to merle, much like the modifiers that affect the S Locus and cause such a wide range of pattering in the white spotted dog (Yousha, 1995). See H/W Locus for another theory of harlequin inheritance.The m recessive is exclusively present in all other Danes who are homozygous recessive; to include blacks, bostons(Mantles), piebalds, boston-heads, head-n-tail spot dogs (i.e. colour-headed dog) from harl/merle breedings; again dogs predominately white are difficult to distinguish as to genotype (i.e. phenotypes possible include MM, Mm, & mmspsp/sw individuals when full pigment restriction is present.)

Locus P: pigment locus; dominant pigment dilution locus proposed to explain lilac/pale eyed animals. Contains 2 alleles.
P = produces dominant paling of all pigment.
p = allows full pigmentation to form.
Present in Great Danes: only recessive p allele.

LOCUS S: Pattern locus; "recessive white locus", or piebald locus which restricts the full pigmentation of the body in a somewhat orderly fashion. Incomplete dominance occurs between alleles & modifiers are present which produce a wide & overlapping phenotype between genotypes. Modifiers are thought to be independently inherited from the main
locus. Contains 4 alleles.
S = allows for self-colored dog with no more than 10% body white confined to the toes and chest when full extension of negative modifiers present.
si = 'irish pattern'; produces an extension of white from 10% to 30% in a symmetrical pattern involving some or all of the following areas: feet/lower legs/belly/chest/tail tip/collar & blaze. Commonly produces what North American Dane breeders refer to as "mismarks"--i.e. white trim on a pigmented dog. Recessive to S. With strong positive modifiers indistinguishable, phenotypically, from an SS genotype. With strong negative modifiers indistinguishable, phenotypically, from an spsp dog with positive modifiers.
sp = "piebald pattern"; produces a wide range of variation in color percentage & location of pigmented areas. Individuals with a full collar, blaze, white legs, belly & tail tip to individuals with only head and tail root color are possible: white from 10% to 90%. Less symmetrical than the si allele, with wide variations in phenotype extended by the action of modifiers. S is incompletely dominant when combined with sp, producing dogs who appear, phenotypically, as SS, Ssi or sisi genotypes. Note modifiers are thought to be inherited separately from the S locus, and thereby recombine in progeny with a wide
variation of resulting phenotypes. Typically produces "flashy" bicolored dogs such as seen in the beagle & pointer; 'split-headed' harls & harls typically with one side of body/.head radically different in pigment distribution would also likely be typical expressions of the piebald allele.
sw = "extreme-white piebald" restricts pigment to 10% or less: if pigment is present, confined to the head & tail root. Negative modifiers produce all white dogs. Harl/boston/merle "head" dogs results--as do "head & tail spot" dogs--dogs typically with no body patches except at tail root & on the head around the ears/eyes. Incompletely dominant when combines with S or si to produce dogs who appear as spsp individuals in phenotype (i.e. pseudo-Irish or pseudo-boston dogs).
Present in Great Danes: All but harlequin family are (normally) homozygous SS--- Harlequins are thought to be spsp historically, however there are certainly Ssp heterozygotes, and some feel both the si and sw alleles are also present. As modifiers have increased action as white extends, & the piebald allele produces some a wide variation in the color-patterning of progeny of spsp homozygotes, it is difficult to predict/control the effects of the sp allele. As spsp dogs can appear of similar phenotype to spsw, swsw, Ssp, Ssw, sisi, predictions of progeny are often poor & pedigrees are difficult to mark. spsp, spsw & swsw with the appropriate modifiers may be indistinguishable, phenotypically from MMs?-- animals, as the dominant white/merle allele is only certain if the midtone (grey) patches or blue eyes are present. mmspsp dogs can be mistaken for Mmspsp or MMspsp, and be designated as harls. Although possibly correct for the standard, dogs appearing with appropriate white, but lacking the M allele, are unable to contribute to harl/merle offspring. (They are likely to have rather round spots with smooth edges & thus be disqualified.) Test breeding may be required of mostly white animals to determine their genotype, if such dogs are not routinely culled out of breeding programs (for the obvious danger of producing an increase in mismarks).
The breeding and stabilization of Mantledanes, particularly the recognition of homozygous sisi or spsp Mantles & identification of heterozygote Mantles, as well as the culling of abberant Black & White Danes (e.g., "mismarked" blacks & nearly white & piebald dogs) can help fix a firm background of recessive white alleles upon which the dominant white (M) locus can act. The Loci S & P (and their modifiers?) seem to act in a (somewhat) synergistic manner, as Mantledanes with broken collars & even mismarked blacks can be siblings to Harlequins carrying rather more white than what would otherwise seem to be their genetic equivalent (i.e. mmspsp vs. Mmspsp).

LOCUS T: Pattern locus. "ticking locus" produces pigment spots on areas of white coat color.
Contains 2 alleles.
T = dominant Ticking allele
t = recessive non-ticking
Present in Great Danes: only recessive t reported.
Ticking appears in the first week of life: typical breeds are the Dalmation (swswTT) & the ACD (sp/swTT). The 'ticking' or rather salt and pepper background on harls that is less prefered to a pure white base coat is not likely caused by the ticking allele, but rather is a product of pigment cell migration & possibly an after effect of the documented instability of color in merle & harl dogs.

Locus R: proposed roaning locus with possible dominant action.
2 alleles. Not reported in Great Danes.
Roaning is separated from ticking as it seems to increase pigment slowly over the life of the dog, "filling in" areas of white with pigmented hairs. If it's action were to be considered as recessive, (or ?), it could possibly be employed to explain the phenomena of pigment cell migration that makes members of the harl family show an increase in pigmented hairs/skin in areas of white (e.g. dirty coats, "ticking"). See ticking & T Locus above.

Locus W/H: (Bagala 1966/Sponenberg 1985) Proposed dominant white/harl locus that produces the harl pattern when the M allele is present: "takes the mid-range (grey) pigment to white". Lethal when homozygotic; if present predicates a 25% reduction in offspring from harl x harl matings. Merles would not carry this. (NOTE: If modifiers are present at the M Locus, as at the S locus (Yousha1995), these could account for the variations seen in harl & merle coloration without having to invent a gene undocumented/unknown in all other dog breeds. If harls are genotypically merles and the variation from "clean" to "gray" background is simply phenotypic and/or results from the action of S Locus modifiers/synergy (Little 1955).)

Lethal WW/HH (*note this requires a minimal reduction in litter size of 25%, and combined with the observed 50% lethal rate for MM; harl to harl breedings would result in litters consistently 37.5% smaller than those of solid Danes. This does not seem to be reported & the authors of such theories have not addressed this issue.) Harls WwMm Merles wwMm Black/bostons wwmm (?Wwmm) (WW mm presumed lethal, but why that would be so in mm dogs is also not addressed.) These blacks carrying for W would, in any case, as with a theory of modifiers (Yousha 1995), allow for individual boston-black dogs to contribute unequally to the production of harlequins (i.e. a Wwmm black COULD produce harls off a Mmww merle, for example, as well as increase the production of harls (WwMm x Wwmm) over a mmww boston-black. Hybrid White--A'-B-C-D-E- Mmspsptt (or spsw or swsw). These whites are a merle heterozygote and appear as MM whites or as very lightly marked harls, harl-heads or even porcelains (e.g. merlikins). They also contribute to the white extension that results in loss of body spotting, and will not breed as expected for a (MM) white. For more on this issue see the references here.

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EXAMPLES OF GENOTYPES OF STANDARD COLORS
(dashes - represent unknown second allele, as dominant allele is present & the animal may be homo- or heterozygous at this locus)

Fawn: ayayB-C-D-Em-ggmmppSStt
Brindle: ayayB-C-D-EmebrmmppSStt (Eebr or ebrebr also exist.)
Black: A'A'B-C-D-EEmmppSStt
Blue: A'A'B-C-dd EEmmppSStt

(Variations in genotype are possible, where recessives such as b=blue are carried by heterozygotes & will only be expressed in phenotype as a result of a hetero x hetero mating which will produce, statistically 25% offspring with the recessive phenotype)
For example: Black (A'A'B-C-DdEEmmppSStt) x Black (same) produce 25% dd = blue offspring; the same applies to blacks producing chocolates, irish/piebalds, fawns & brindles, and fawns/brindles producing blue/chocolate masks/stripes and irish/piebalds. Note Black can "hide" all the other acceptable, as well as some unacceptable colors and appear solid black.

Harlequin: A'-B-C-D-E-Mm(spsp)tt(Ww)
Merle: A'-B-C-D-E-Mm(S/s)tt(ww) (same genotype?/lacks modifiers?/lacks H=W?/)
Mantle: A'-B-C-D-EEmmspsp(ww)----- (note this black differs in genotype from above described solid black and appears as "mismark/boston/piebald/boston head/ head and tail spot", depending on the type of modifiers present. For more on the topic, see Mantle Genetics, or the article Spots Before Your Eyes.

White: "double-merle/dominant white" = A'-B-C-D-E-MMspsptt(ww or Ww). Dominant-whites with correct modifiers/or who carry the W=dominant white allele could produce harls; dogs that carry a different set of modifiers and no would be unable to produce harls. **Phenotype, however, would appear (nearly?) identical.

White: "white-factored harlequin" = A"-B-C-D-E-Mmsp/e(Ww). This is essentially an undermarked harlequin, just as the piebald white described below is an undermarked Mantle. Will contribute to the production of mismarked (white bodied, colour-headed, dogs).

White: "pieblad piebald/recessive-white" = A'-B-C-D-E-mmspsptt (or spsw or swsw/depends on the modifiers present). These whites cannot contribute to the production of harl/merle offspring; but will contribute, recessively, to the extension of white/lack of body pigment.
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EXAMPLES OF 'TYPICAL HARL-TYPE BREEDINGS:
(black includes all black and white offspring: mismark/boston/piebald/boston-
head/extreme piebalds) (White progeny is restricted to MM "double-merle/dominant" whites).

harl x harl = 25% merle(Mm), 25% black(mm), 25% white(MM) & 25% harl(Mm)
(if whites have reduced viability, these embryos would die, giving a smaller percentage of whites born).

harl x black = 25% merle, 50% black, 25% harl (no MM whites are possible).

white (MM) x black (mm) - all merles &/or harls (assuming white is fertile)

harl x merle = as harl x harl; 25% of each 'four colors'

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PROBLEMS ASSOCIATED WITH HARLEQUIN BREEDING

(problems that do not generally afflict the other colors in the Great Dane breed)

1. Harlequins, being heterozygotes, cannot breed true; i.e., cannot reproduce themselves consistently in either phenotype or genotype.

2. Loss of possible progeny due to MM and/or WW reduced viability?

3. Difficulty in controlling color patterning and amount of pigment even when correctly marked individuals are consistently bred to each other; multiple incorrectly marked harlequins--or well-marked harlequins of inadequate breed type, conformation and soundness.

4. Multiple mismarks produced in every litter: reduced number of show/breed stock to select otherwise correct/superior individuals; high number of pets-by-markings produced.

5. Genotype of near-white individuals cannot be determined based on phenotype; test breedings may have to be performed to determine genotype, (if these animals are kept for potential breeding stock, rather than culled): which requires raising & rearing mismarks which may prove useless for breed improvement. (The same applies to mismark blacks, who lack correct boston patterning genetically.)

6. All near-white and white individuals should be checked for hearing and eye anomalies if not euthanized at birth.

7. Modifiers at the S (and possibly M) Locus inherited independently of the main gene, and both Loci are incompletely dominant, leading to unpredictable pattern variations in offspring and mismarks from correctly marked stock.

8. All stud contract/co-ownerships must be carefully read and agreement of which color-type individuals will be euthanized at birth/how all mis-marks must be handled (e.g. how culled, euthanized, limited registration, spay/neuter contracts) must be settled between attendant parties.

9. It is not uncommon for litters to include only 1 or 2 correctly marked (harl) offspring. Further, many of the mantle offspring will be poorly marked for consideration as breeding stock. Successive litters may contain no correctly marked offspring/or the correctly marked offspring present may be the least adequate in all other breed features. The sex desired in often unavailable in the desired color pattern.

10. After careful consideration, most breeders interested in consistently producing quality stock turn to one of the other acceptable colors in Great Danes, where this is more likely to be a reality; therefore, this, combined with the low number of animals acceptable as breeding stock means there is a reduced gene-pool in the harlequin family. Also the color attracts many novices who are unable/unwilling? to learn enough about the breed and the harl variant to produce correct specimens, as well as some unsavory individuals who exploit the novelty of the color and produce entire lines for sale to the pet market, with high prices and 'rare' colors offered. Pet homes must be judiciously screened to avoid homes who are more interested in owning "the spots" than the breed, and limited registrations/spay and neuter options must be rigorously enforced to avoid "spawning" situations where more poor-quality 'spotted' Danes are ultimately bred.

** A few knowledgeable, dedicated individuals with a flair for genetics, a good eye for a dog and a gambler's heart carry the Harlequin variant through history. (Many more who are mating harl bred dogs know only enough about the variant to be dangerous to the breed.)

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