19.8: White spotting - when there's more than two alleles

So far, we have discussed genes which have only two alleles. However, that is not always the case: there can be more than two alleles for a given gene. One example is the MITF gene, which is the major gene that controls white spotting in dogs. This protein is required for the migration and survival of melanocytes into the skin during development. If it is not functional, it impairs the ability of the skin to make pigment, thus “covering up” the effect of other color genes. There are thought to be at least four alleles that can contribute (Karlsson, 2007). Depending on which alleles are present in a dog, the amount of white can vary from none (a solid-colored dog) to mostly white (Table \(\PageIndex{1}\) and Figure \(\PageIndex{1}\)).

Table \(\PageIndex{1}\): Combinations of different alleles for MITF result in different amounts of white present in the coat.

Alleles	Amount of white
SS	None (solid colored)
Ssi	Small amounts of white possible on face, chest, feet, and tail tip
Ssp	More than 50% solid colored, with white on the face, chest, feet, collar, underbelly, and tail tip
sisp	Approximately even amounts of color and white
sise	More than 50% white with irregular splashes of color
sese	Mostly white with only minimal areas of color, perhaps on one or both ears, an eye patch, or a spot near the tail

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