B Locus
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The B Locus, referred to as Eumelanin or Black Shades, controls the hue of the eumelanin present in dog coats. Currently there is only two known eumelanin shades in dogs, "Black" and "Liver". The presence, presentation, and amount of eumelanin is modified by the majority of known genes.
- BB or Bb = Black
bb = Liver
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Co Locus
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The Co Locus, aka "Cocoa", in French Bulldogs is a modifier to eumelanin which makes it look very similar to Liver, but is on a different loci! It is currently unknown what would happen if it modified Liver, but typically the modification is to Black. These similarly can be diluted to a color that is also unique to this modifier.
- CoCo or Coco = Non Cocoa
coco = Cocoa
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D Locus
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The D Locus, aka Dilution, effects the pigment in Eumelanin (and Cocoa)
- DD or Dd = Dense
dd = Dilute