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These tables show the effect of the dilution genes on the three basic colors of black, bay, and chestnut (which is basically the same as sorrel).

There are four genes that dilute the three basic colors. They are the cream gene, c, the dun gene, D, the silver dapple gene, Z, and the champagne gene, which is fairly newly documented. Click here for information about the champagne gene. The other dilutes are discussed below.

The c gene dilutes red to yellow. It is the gene responsible for palomino and buckskin. In its heterozygous form (Cc), it changes red or flaxen mane and tail color to white, but leaves black mane and tail color alone. c has little effect on black. Black horses who inherit the gene may be slightly diluted to an off-black color. The dominant form of the gene, C, is known as an incomplete dominant. A horse that is heterozygous for C (genotype Cc) has its color partly diluted from red to yellow, while a homozygous cc horse is diluted more, from yellow to cream. (Homozygous CC horses are not diluted.)

Table 1: Effect of the cream dilution gene, c, on chestnut (ee) horses.

Table 2: The effect of the cream dilution gene, c, on bay (A-E-) horses.

The D gene also dilutes red to yellow, and dilutes black to slate. It is responsible for dun, red dun, and grulla. It never affects the color of the points (mane, tail, lower legs). Also, it's a complete dominant, so the phenotypes of the heterozygous and homozygous possessors of the D gene are identical.

Table 3: The effects of the dun dilution gene, D, on chestnut (ee) horses.

Table 4: The effects of the dun dilution gene, D, on bay (A-E-) horses.

Table 5: The effects of the dun dilution gene, D, on black (aaE-) horses.

The Z gene, which only affects black, is found only in a few breeds, most notably the Shetland. Although it is called the "silver dapple gene," it has nothing to do with dapple grey. Instead, the Z gene dilutes the black body of a horse to a flat brown shade, usually but not always with dapples, and dilutes the mane and tail to white. The body may be a medium brown or a very dark brown. Due to the white mane and tail, these horses are often confused with palominos. On bay, the Z gene dilutes the mane and tail to white and the black legs to flat brown, usually with dapples, but the red body color is unaffected. Like D, Z is a complete dominant, and heterozygotes and homozygotes appear the same.

Table 6: The effects of the silver dapple dilution gene, Z, on black (aaE-) horses.

Table 7. The effects of the silver dapple dilution gene, Z, on bay (A-E-) horses.

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