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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 seven loci discussed on this page are: A, C, D, E, Uw, P, and Sp. The loci not discussed include the Semi-Dominant Lethal Spotting, Rex, and Wavy mutations, none of which are 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.
A: The base of the hair shaft is a dark gray, but is not usually visible unless the fur is parted.
B: The middle band is a golden brown. Because of the way the individual hairs of the coat overlap, this middle band is the most visible, and contributes most to the perceived overall color.
C: The tip of the hair is black, which gives rise to "ticking", the stippled appearance of colors such as Agouti and Nutmeg.
This gray-brown-black pattern causes the wild-colored coat to appear a dark brown.
The recessive allele at this locus, p, causes the normally black eyes to lighten to red, as well as diluting the color of the coat. The black pigment is affected more than the yellow pigment, especially the black hair-tips.
A- C- D- E- Uw- P- :: Agouti A- CC D- E- Uw- pp :: Argente Golden
Interestingly, having two recessive alleles at the P-locus modifies the dominance hierarchy at the C-locus, making C no longer fully dominant. What this means is that there is a noticeable difference between a CCpp gerbil, a Ccchmpp gerbil, and a Cchpp gerbil -- whereas a C-P- gerbil will have the same color regardless of what the second allele at the C-locus is.
aa C- D- E- Uw- P- :: Black aa CC D- E- Uw- pp :: Lilac (facing right)
aa Ccchm D- E- Uw- pp :: Sapphire (facing left)
!!! aa Cch D- E- Uw- pp :: Dove