The Cream dilution gene is responsible for the palomino, buckskin, smoky black, cremello, perlino, and smoky cream coat colors. Cream dilutes red pigment (phaeomelanin) to yellow pigment in single dose (palominos, buckskins, smoky blacks) and to pale cream in double dose (cremellos, perlinos, smoky cream). The cream dilution can have a very subtle effect on black pigment (eumelanin) in the heterozygous state.
The mutation responsible for the cream dilution is in the gene MATP (c.457G>A) and is thought to disrupt the trafficking of pigment molecules to developing melanocytes(pigment producing cells). The cream mutation shows incomplete dominance, so that one copy of the cream allele (heterozygous) produces a dilute phenotype and two copies of the cream allele (homozygous) produces a more extreme dilute phenotype. Mating a cream horse (Cr/N) to a non-cream horse (N/N) will result in a 50% chance of producing offspring with the cream dilution. Mating a homozygous cream horse (Cr/Cr) with a non-cream horse (N/N) will result in cream offspring 100% of the time.
Testing for the cream dilution allows breeders to identify homozygous animals (animals with two copies of the variant) which will always produce cream dilute offspring.
Note: This test is specific for a mutation in exon 2 of the MATP gene that is associated with the cream dilution. Other dilution genes or mutations that may produce coat colors that phenotypically resemble cream will not be detected by this test.
Locke, M. M., Ruth, L. S., Millon, L .V., Penedo, M. C. T., Murray, J. D., & Bowling, A. T. (2001). The cream dilution gene, responsible for the palomino and buckskin coat colours, maps to horse chromosome 21. Animal Genetics, 32(6), 340-343. doi: 10.1046/j.1365-2052.2001.00806.x
Mariat, D., Taourit, S., & Guérin, G. (2003). A mutation in the MATP gene causes the cream coat colour in the horse. Genetics Selection Evolution, 35(1), 119-133. doi: 10.1051/gse:2002039