To date, there are at least ten known loci that control coat color in gerbils; each locus controls a different trait. Each of these loci has a dominant allele, that usually represents the form of the trait commonly found in the wild, and at least one recessive allele, representing a less common form of the trait. The eight loci discussed on this page are: A, C, D, E, P, Uw, Sp, and Re. I will also touch on Steel-factor, which is a different sort of locus. The loci not discussed include the Semi-Dominant Lethal Spotting and Wavy mutations, which are not known to be present in the USA at this point.
To understand how these loci work, it is necessary to know how color is structured on the hair.
One of the newer color mutations to appear in gerbils is the dilute allele, d. This mutation causes pigment granules in the hair shaft to clump together on a microscopic level, diluting the overall color. Because the clumps seem to form randomly, the dilution is extremely variable and can cause a ticked appearance. The eye color is also diluted, with a garnet glow in bright light.
In contrast to the C-recessives, Dilution affects eumelanin (black pigment) much more than phaeomelanin (yellow pigment). Dilute Agouti can look almost like a black-eyed Argente.
Dilute gerbils were imported to the US from Finland in 2008, and are still somewhat rare.