Understanding The Primary Coat Colours
If we take the known mutations that have occurred in the gerbil, how would these individual mutations look on an Agouti coat colour? We know that the Agouti coat is the natural colour of the Mongolian gerbil; it aids in camouflage and helps it to blend in with its surroundings. The white belly serves a purpose too and aids in thermo-regulation in the extremes of its natural climate. However, in captivity there is neither the need for camouflage or thermo-regulation, so a new mutation that affects the coat colour can flourish through succesful breeding and selection.
So let's take a look how these coat colour mutations affect their natural coat colour to form the primary coat colours in the gerbil. Of course, if we start combining several of these recessive genes, many other coat colours appear, but firstly, we need to understand how these mutations change the coat colour in our Agouti gerbil, and secondly in a Black (self) gerbil.
Loci and genes are usually denoted by a letter to indicate the specific characteristic that is carried out at that particular gene. An example of this is the Agouti locus. This locus controls whether the gerbil has banding in the hair and a white belly. This is the wild type, or natural colour of the gerbil and is denoted by the letter 'A'. We use a capital letter to denote a dominant characteristic. For a recessive characteristic we use a lowercase letter. The recessive gene at this locus is denoted 'a', this removes the banding in the hair and removes the white belly, however, because it is a recessive gene, it would require two of these genes for it to have a noticeable effect on the coat colour.
AA = Golden Agouti
Aa = Golden Agouti
aa = Black.
In all the genecode examples below, they have been written with the intent of showing all the loci as wild genes except for those at the loci that are affected by the relevant mutations being discussed. In reality, with all these different coat colour mutations circulating in the gerbil gene pool, even our humble Golden Agouti can carry many recessive genes. For example AaCCDdEePPUwuw(d) would still be a Golden Agouti, because the Golden Agouti still has a dominant gene at each locus, and the recessive genes have no real effect on its colour. In this case, and for the purpose of notation, any of the loci where we are unsure of what gene is lying there we denote as - or *. So, for a Golden Agouti of unknown ancestry, we simply write A*C*D*E*P*Uw*
The Agouti Locus
So here's our Golden Agouti gerbil. Now before any colour mutations occurred it had dominant or wild genes at each of the known loci, these being AACCDDEEPPUwUw
The Black or non-agouti mutation causes a dramatic change to the Agouti coat. It completely removes the white belly and takes away the yellow band from the hair shaft in the Agouti coat colour. The end result is a black coated gerbil.
With the occurrence of the non-agouti mutation we now essentially have two distinct coat colour types. The White Bellied type and the Self type. These two distinct coat colours form our two base colours from which we can apply further mutations to, which will in turn further change the coat colour. From here on in we can see how the rest of the known mutations change these two standard coat colours.
Chinchilla Medium (cchm)
With the occurrence of two recessive mutations at the C locus, they enabled the Agouti and the Self Black to change coat colour once more. The C locus controls the amount of colour intensity in the coat, and the Chinchilla Medium mutation alters the colour by removing most of the yellow from the coat, but leaves the pigment relatively unaffected at the gerbil's extremities. The 'points' are the feet, nose, ears & tail. On an Agouti coat colour this gives rise to the Chinchilla Medium coat colour otherwise known as Colourpoint Golden Agouti.
On a Self Black coat the same mutation gives us the Colourpoint Black, also known as the Burmese Coat colour variety.
The second mutation at the C locus is known as Himalayan. It essentially acts in a similar manner to the Chinchilla Medium mutation, but is extreme in its actions, and leaves pigment only at the tail. It also has the ability to remove the pigments from the black eye colouring, turning them red. On an Agouti coat it produces a coat colour known as the Dark-Tailed White. On Agouti, the tail is a light sepia colour and it often takes many months for any colouring to appear on the tail.
On a Black coat, it again produces a Dark-Tail White, but this time the tail is much darker and has a rich brown hue. Both of the genes at the C locus, c(chm) and c(h), are temperature dependent, and in the cooler areas of the body the mutation doesn't work too well, so it has less ability to dilute the coat colour.
The next Locus is the D locus. This controls the depth, or intensity in a gerbil's coat. A recessive mutation here dilutes the coat. In a gerbil, this mutation works by diluting the black pigments in the coat, and only slightly dilutes the yellow pigment. On an Agouti coat it will mostly dilute the black areas of the hair (the undercoat and the ticking) the colour giving the gerbil a slightly washed out appearance.
On a Self Black coat the change is more dramatic, producing the well known Blue coat colour variety.
Extension of Yellow (e)
The following Locus is the E locus, or the Extension Locus. This locus is responsible for controlling the balance between the black and yellow pigments in the coat. To date, two mutations have occurred at the Extension Locus. The first mutation is known as the extension of Yellow. On an Agouti coat this mutation produces the well known Dark-Eyed Honey coat colour.
On the Self Black coat it has a very unusual effect as the gerbil matures into adulthood. As a pup, the gerbil is a yellow colouring, but as it moults into its adult coat it develops exaggerated black ticking to the hair which results in the Nutmeg coat colour.
Fading Yellow (ef)
The second mutation that occurs at the E locus is Fading Yellow. The gerbil pup is very similar to the Dark-Eyed honey pup and is a rich yellow colour, however as it ages and moults, the yellow coat fades to an off-white, leaving pigment only at the nose and tail. This is known as the Schimmel coat colour. On an Agouti coat the mutation turns the coat to off-white, and the nose and tail are a light yellow colour.
On a Self Black the effect is very similar, however the nose and the tail are a richer yellow colouring.
Pink-Eyed Dilution Locus
Pink-Eyed Dilution (p)
The mutation here is known as the Pink-Eyed Dilution mutation. On an Agouti coat it removes virtually all the black pigment and turns the eye colour to ruby. This coat colour is known as Argente Golden.
On a Self Black this mutation results in the Lilac coat colour variety.
This gene appeared in 2000 and isn't in wide circulation. It is a recessive allele of the Underwhite Locus, and is allelic (genetically related) to the Grey Agouti. The gene has a particulary strong diluting effect when homozygous on either 'A-' or 'aa' coat varieties, and even if black-eyed it will dilute the black eye pigment to a dark ruby, and the coat to cream colour.
Geneticists gave it this name because on Agouti their undercoats are white. Even on A- type uw(d) gerbils we can see the 'underwhite' effect happening.. Take the White Bellied cream coat colour for an example, if we gently part the fur we can see their white undercoat , the same can be seen on Agouti uw Cream (See below)
The uw(d) allele controls the intensity of the yellow and black pigments in the coat. The recessive mutation at this locus reduces the intensity of these pigments. It also slightly dilutes the pigments in the eye. On Agouti gerbils it will dilute most of the yellow pigment in the coat to a cream shade, but will also slightly dilute the black pigment as well. The end result is the Grey Agouti coat colour.
On a Self Black coat colour the black pigment is diluted slightly to produce the Slate coat colour variety. In this photo the eye dilution effect is quite noticeable, giving the gerbil the familiar red 'eye shine'.
Dominant Spotting Locus
Dominant Spotting (Sp)
As its name suggests, this mutation is dominant in nature. Rather than being viewed as a coat colour, it is seen as a pattern that overlays any existing coat colour. So white spotting can occur on any coat colour variety. Along with the spotting mutation there exists modifying genes(polygenes; poly meaning many) which act on spotting to extend its markings.
These modifying genes enable the gerbil to have an extensive range of white markings from the simple spot to the variegated coat colour variety, as seen below in our colour strip.
Semi-Dominant Lethal Spotting Locus
This is the second spotting locus in the gerbil. With Dominant Spotting the homozygous pups are never born, but are usually reabsorbed in the womb and get replaced by viable embryos. This isn't the case with Lethal spotting, and the homozygous pups are born. These pups are known as 'Rumpblacks'. Unfortunately the Rumpblack pups die, either very early in life or around the time of weaning. On a black coat colour the effect of the spotting is minor; usually they have some white on their paws and hind feet and an exaggerated white neck 'bib'. Sometimes, but not always, this is accompanied by a spot on the nape of their neck and a small 'bikini line' spot on their belly. Their toenails are also odd in colour, some being pigmented while others remain clear. On Agouti, the spotting may even go unnoticed as it already has a white belly and white feet. The only way to be sure is to check their toenails to see if some lack pigment. For this reason, and because of the potential dangers of this gene, it is never recommended to cross this gene to any A- type gerbils. Because this spotting gene co-operates with Dominant spotting, it has the ability to produce gerbils with an extreme amount of white patterning on them. However many of these gerbils have health problems.
Below are two useful flash demos that show you at a glance how the various mutations affect both the Agouti and the Self Black coat colours. Click and hold the button down to see how each mutation changes the coat colouring.