Whitmoregirl's Wombles

I find that a lot of gerbil owners are confused to what purpose the white markings on their self (coloured belly) gerbils serve.

Well, they don’t serve a purpose per se, but for breeding they do serve a very useful indicator of what kind of spotting patterns you may get should it be bred to a spotted gerbil. *

* Just to clarify, pale and white gerbils and white bellied gerbils do carry these markings, but because of the white on their paws and bellies, you obviously cannot see them, it’s only because of the coloured belly on ‘aa’ types that you can see them.

The spotting in gerbils is unlike most other species, whose spotting is recessive. Gerbil spotting is called Dominant Spotting because it is dominant!, meaning that if the gene is in the animal, it’s characteristics will always appear in the phenotype (ie what the animal’s physical appearance).

Spotting is odd in gerbils, in that there doesn’t seem to be any equivalent recessive at that loci, a gerbil either has it or doesn’t, so if you breed from a spotted gerbil, on conception the embyro is either spotted or it isn’t.
Dominant spotting causes a very mild form of anaemia in gerbils. Embryos with two copies of the gene (SpSp) tend to die before birth because of very severe anaemia; in some extremely rare occasions, some of these pups have came to full term but are either still-born on birth or die shortly after, although this is exceptionally rare and more often the embryo will die in the womb and is simply reabsorbed and replaced.

Because this usually happens so early in the pregnancy, and gerbils produce more embryos than can implant anyway, the number of pups in the litter is not affected. There is a page going into more detail on this on eGerbil, Spotted gerbil litters, which is worth a read

So, if you’ve got your litter of spotted and non-spotted gerbils, you can tell from first glance who has dominant spotting and who hasn’t, with the exception of PEW, REW, etc!
There are some spotted gerbils that have such minimal spotting, that the naked eye cannot detect it, such as if the gerbil only has a few hairs of white on its neck or forehead.
However, (depending on the base coat), you can tell a dominant spotted gerbil apart from a non-spotted gerbil by its’ nails as the dom. spot gerbil will have clear nails, while a non-spotted gerbil will have coloured nails, with the exception of most ‘gg’ and ‘c(-) c(-) pp’** type gerbils.

**for example a colourpoint argente (aka Pink Eyed White), AA c(chm)c(chm) EE GG pp, due to the chinchilla medium + pink eyed dilution the nail colour is wiped out like the coat.

Left: Spotted black gerbil. Right: Dom. Spot carrier.

So this leads us back to question of this post! What are dominant spot carriers?!

Well, as you can see from the photos above, the dominant spot carrier gerbil has a large amount of white on its paw. If you turn the gerbil over, you will also note a ‘bib’ of white around its mouth and sometimes running down its throat, which can vary in size as can the white on the paws, for example this gerbil..

.. which has very little white on its paws and mouth.

The variance of the white is the indicator to a breeder of what kind of spotted lines the gerbil has came from, ie a gerbil with very little to no white chin or paw markings, a breeder will assume that the line has very little to no spotting.
A gerbil with a massive bib and sometimes pure white paws will be able to assume that the gerbil is out of an extensively-marked line (however this does not mean it has came from a mottled line, as it could just as easily be from a largely patched line.

(if you’re unsure on the different ‘types’ of spotting please see the eGerbil spotting gallery)

In a nutshell, what breeders term a dominant spot carrier is just the solid-type gerbils coming out of spotted lines. These gerbils carry the white modifying genes for spotted, patched, collared, mottled etc varieties. If you cross a “carrier” from any of these lines to a spotted gerbil you’ll get these modifying genes affecting the crosses.