HARLEQUIN COAT COLOR GENETICS
by Neil O'Sullivan, Ph.D.
Author of Harlequin colour in the Great Dane dog (1989 Genetica) and Chair of the GDCA Color Research Committee. This document constructed using the handout given to participants in a lecture of the same name at the 2000 GDCA Great Dane National Specialty. Please see also Jane Chopson's report on INHERITANCE OF GREAT DANE COAT COLOR for a more detailed explanation. This theory called by some Harl-factoring, would more formally be referred to as the Sponnenberg Hypothesis (first published in 1985).
In this discussion the following major & minor coat color genes are relevant:
A series: A^s=black pigment & a^y=fawn pigment.
H series: H=harlequin & h=non-harl. HH is always lethal to the embryo.
M series: M=merle & m=non-merle. MM is a semi-lethal & ~50% die, many surviving are defective.
S series: S=solid pattern & s^i=mantle pattern. (Blacks/Mantles are treated as one category.)
T series: T=dominant ticking & t=non-ticking.
Tw series: Tw=normal harl/merle pattern & tw=merliquin pattern.
For the purposes of this discussion fawn, blue, brindle & the piebald as a seperate phenomenon are ignored.
HARLEQUIN: A^sA^s Hh Mm
MERLE: A^sA^s hh Mm
WHITE: A^sA^s Hh MM (harl-factored) or A^sA^s hh MM (note "whites" can be up to 10% pigmented)
BLACK(MANTLE): A^sA^s HH mm (lethal) or A^sA^s Hh (harl-factored) or MmA^sA^s hh mm
HarlxHarl: of the 16 possible combination four (25%) are HH lethals, leaving one with 33.3% Harlequin, 25% Black-Mantle, 16.6% merle & 25% white expected. Note that these MM whites are semi-lethal so that one usually sees less than the expected ratio actually born live. So this gives potentially 7/12 show-marks (58.3%).
HarlxMerle: of the 8 possible combinations two (35%) are semi-lethal whites, with 25% each expected of Harlequin, merle, white, and Black-Mantle. Note this is a lower rate of show-marks (maximum 50% possible) than what is expected from a harl to harl breeding as merles do NOT carry the harl-factor so cannot contribute to the production of Harlequin offspring.
HarlxBlack-Mantle: there are two different kinds of Black-Mantle dogs--those who are harl-factored and those who are not (& you cannot be sure if a Black-Mantle is harl-factored until you breed him). If a harl-factored Black-Mantle is used, expect 50% Black-Mantle, 33.3% Harlequin and 16.6% merle (or two harls for each merle produced). If a non harl-factored Black-Mantle is used, then the ratio of harls-to-merles is one-to-one. Black-Mantles remain 50% of the litter with 25% each Harlequin/merle expected. So in this case you can expect from 75% or more of the litter to be potentially show-marked.
HarlxWhite: again there are two possible kinds of whites: harl-factored whites and non-harl-factored whites. If the white used is harl-factored then expect 50% white with 2 Harlequins for every merle. If the white used is not harl-factored expect 50% white with the other half of the litter split evenly between harls and merles. And recall that some whites will die and others will have eye-ear, etc. defects as this is a semi-lethal gene combination. About 3/4 of this litter is disqualifying in color with about 1/2 of them carrying a semi-lethal gene combination.
WhitexBlack-Mantle: since white can have one of two genotypes and Black-Mantle can also have two different genotypes, there are four possible breeding combinations here. When both partners are harl-factored there are two Harlequins produced for every merle. When only one parent is harl-factored, there is a 50/50 split between Harlequin and merle puppies. When neither parent is harl-factored, the litter is all merles. "White to black only works if one or both parents are carrying for the harlequin allele."
WhitexMerle: 50% of this litter is expected to be white. If the white is harl-factored there is one harl for every merle, if not then only merles are otherwise produced. Merle cannot aid in the production of correct color.
Black-MantlexMerle: again the production of Harlequins rather than merles depends on whether the Black-Mantle is harl-factored or not, as merle cannot aid in the production of Harlequins. If the Black-Mantle is harl-factored expect one Harlequin for each merle and each Black-Mantle. If the Black-Mantle is not harl-factored, expect a 50/50 split of Black-Mantle and merle puppies.
As you can see from the above the Harlequin is a dual heterozygote by definition, carrying one gene for harl-factoring and one merle gene. It should be clear from the diagrams presented why the Harlequin will never breed true. Other important points noted are that (a) merles lack the harl-factor by definition and cannot contribute to the production of Harlequin puppies, that (b) Blacks (incl. Mantles) and whites (white merles) can be harl-factored or not and only if they are harl-factored can they contribute to an increase in the percentage of Harlequin puppies expected.
A few more notes from Dr. Neil O'Sullivan: "You will note that the use of deaf whites is highly correlated with more deaf whites in the progeny or grandprogeny. Also the use of deaf whites and deaf merlequins correlates with a higher incidence of deafness and eye defects even in the harles."
"In short...I think breeding from deaf dogs is not smart as it increases the frequency of genes which do not encourage pigmentation of the head and thus middle ear and retina and in so doing not only set us up for more deaf whites but deaf merlequins and deaf harlequins too. Yes, deaf harles, as you know from rescue are not as rare as we breeders would like." (The general anecdotal estimate is that 90% of whites are deaf and 50% have defined eye defects. Assumably the estimate for merliquins is not dissimilar.)
"A harlequin is HhMm in genotype with the gray of the merle genotype converted to white by the Hh genotype. Thus the Harlequin is predominantly a white dog with black torn patches, a merle is (hh Mm) a gray dog with black torn patches and a merlequin is a modified merle ( hh Mm tw tw). A harlequin with tw tw ["merliquin"]genotype is usually a "mixed" color [e.g. swirly-merle, harlie-merle or popcorn harl] with almost as much merle as black patches. Tw the non tweed allele is dominant." And a TwTw Harlequin is the dog who will not produce these recessive "tweed" mismarks. Tweed produces a merling pattern with more variation in shades of patches and generally larger patches (or more larger patches).
For more on Harlequin genetics, click here