and Cathy Bickel
Gerbil coat color is controlled by only seven genes whose combinations are fairly well understood.
In gerbil genetics, capital letters represent dominant and lowercase letters recessive. When used, the dash or asterisk symbols mean that the second gene can be either dominant or recessive; the effect is overruled by a dominant first gene. Dominant and recessive genes are easily demonstrated in humans by blue and brown eye color. If one of your parents is blue-eyed and you are brown-eyed, you carry a recessive blue-eyed gene, your genotype. It isn't visible in your appearance, your phenotype, but if you marry a blue-eyed person and have children, statistically half of your children will be blue-eyed and half brown-eyed.
Agouti is the original color of wild gerbils. An agouti gerbil will have a brown coat with black ticking and a white belly. Agouti gerbils have all dominant genes: A- C- D- E- Uw- P-. In the Agouti’s pedigree, all the letters are capitals so the Agouti’s genetics are all dominant.
When scientists brought gerbils to the United States, breeders bred gerbils together until they saw new colors due to recessive genes. The first recessive seen was aa, which produced a black gerbil.
The Effects of the Different Genes on Gerbil Coat Colors
A,a. A is the Agouti locus. It manages the intensity of the yellow color in the coat, as well as the black tips of the fur. The a gene removes the white belly and the yellow from the Agouti’s fur, resulting in what's called a "self" colored gerbil, where the belly and back are the same, or nearly the same, color. Substitute an aa pair in an agouti and you get a black gerbil.
C, c[h], c[chm]. C is the Color locus, or the Albino locus. This locus is normally used for the albino mutation. As cc does not yet exist in the gerbil, there is no real albino. C will control the accumulation of color in the gerbil’s fur.
- C. The color will, by default, be uniform.
- c[h], or Himalayan, is on the same chromosome as the albinno. This gene fades the main color. This gene is sensitive to temperature changes; the fur will darker on the extremities, where the body is cooler.
- c[chm], or Chinchilla Medium, will fade the main color while keeping the tips of the original color. It’s what creates a colorpoint. This gene is also sensitive to temperature changes; the fur be darker on the extremities, where the body is cooler. A c[chm]c[chm] combination is found in the burmese gerbil, while a c[chm]c[h] combination is found in the siamese gerbil.
D,d. The Dilute locus manages the depth of the color. We currently use the dilute gene to denote blue gerbils, but it is likely that this is not the correct nomenclature, as dilute should dilute all the color, and not just black pigment.
- D will let the color express itself normally.
- d will distance the pigments in the hair, which will reduce the intensity of the color. Fewer black pigments in one place will give a gray tint to the fur, for example. The best-known dd gerbil is the blue, which is a black gerbil with a dd combination.
E, e, e[f]. The Extension of Black locus. This gene controls the level of black in the hair. It is sensitive to stains and fading.
- E will define the extent of the black on the tip.
- e, or extension of yellow, will increase the amount of yellow in the hair at the expense of the black tip. The ee combination results in some favorite golden colors like dark-eyed honey and red fox.
- e[f], or fading, behaves similarly to e, but the fur will become much lighter in color with age. Like c[h] and c[chm] the fading is temperature-sensitive, and the body will be lighter than the extremities.
Uw, uw, uw[d]. The Underwhite locus. It manages the intensity of the yellow color in the coat, as well, as the black tip.
- Uw is the original color.
- uw, underwhite or cream, is a rare gene that reduces the yellow for a cream while removing the black.
- uw[d], underwhite dense, formerly known as G or Gray, will reduce the yellow in the coat for a cream, while lightening the black. The toenails will be lighter in self-colored gerbils, and the eyes will reflect ruby red. The gray agouti and silver nutmeg are two favorite colors sporting the uw[d]uw[d] combination.
P, p. The Pink-Eyed Dilution locus. It controls the amount of black pigment in the eyes and the color of the hair.
- P, on non-pink-eyed, will let the eye remain black.
- p, or pink-eyed dilution, will remove almost all black pigment from the gerbil, slightly dilute yellow fur and change the eye color to pink. Pink-eyed white, lilac, red fox and yellow fox gerbils are some of the colors carrying the pp combination.
Sp, +. The Spotting locus.
- Sp means the gerbil will be marked. Markings can be minimal or extensive, ranging from a single spot to pied or mottled.
- + means the gerbil is wildtype and will have no white markings on the nose, forhead, nape, or tail.
A spotless gerbil can nevertheless carry a spot modifier and produce a mottled line of offspring if paired with a spotted mate.
There are other mutations that will influence the appearance of the gerbil.
Steel. This gene will cause a very slight dilution going from the flank gradually to the stomach. There will also be some white hairs on the body despite the absence of spots, and also on the tail. These individuals also have white under the hind legs. This gene also reacts with Spotting, where there will be a lot of speckles, especially on the tail. When there are speckles, we say that the gerbil is Roan. All Roan are Steel, but not all Steel are Roan.
Dark Patched. In this form of spotting, a spotted gerbil will have its original color diluted. A Dark Patched gerbil is a spotted gerbil with a defined region of the original gerbil color. The shape and size of the dark patch varies.
Re. The Rexoid mutation appeared in the Czech Republic in 2007. Rexoid gerbils are commonly called Rex. A rex gerbil can be recognized from birth by its curly whiskers. The fur of pups is very wavy, but evolves as the pup molts while growing into adulthood. Rex is a dominant gene, which requires a single rex parent for 50% of the offspring to be rex themselves. Mating a rex to another rex will result in some of the offspring carrying double-rex, ReRe, which is a semi-lethal combination. Double-rex do not survive for more than 18 months, lose their hair and show signs of serious health problems, such as the development of cataracts. Rex breeding must therefore be done in a responsible manner. Standard-haired babies born to a rex parent usually have fur that is somewhat longer than the fur of regular gerbils.
- ++. Gerbils is wildtype and has standard hair.
- Re+. A rex gerbil carrying one copy of Rex.
- ReRe. A double-rex gerbil; this gerbil will have health complications.
Many thanks to Steph Couture, who gave permission to use work on her website, and to KJ Fuller, for her contributions.