Uw: Underwhite (aka G: Gray)
updated November 15, 2016
Here's a gene with a confused identity. When gray agouti gerbils first appeared, the locus was named G for the fact that the mutation turned gold to gray in agouti gerbils. That's how the official scientific publication christened it, so that made it official. Everyone got used to writing G and g.
More recently, another mutation showed up that turned out to be related. This gene turned gerbils cream. Suddenly gray didn't seem like such a great name any more!
There is an obscure mutation in lab mice that is similar to what we'd seen in gray and cream gerbils. It was called underwhite. Here is a possible set of genes that might explain what we had in gerbils. Underwhite in mice lightened the eyes slightly, just like in gerbils, and lightened the coat in similar ways also. It's not quite the same though, as in mice the back of the animal is darker than the belly. But genes don't always look the same from species to species.
One of the many discoveries in genetics was that the same genes often occur in many different species. Even completely unrelated animals can have exactly the same genes. In the interests of helping science sort out all these genes, whenever practical it's good to give the same name to the same gene no matter what species it's in.
And that brings us back to G. Turns out G is already in use for a gene called Progressive Graying in some breeds of dogs and some horses. It makes animals turn gray as they grew to adulthood (long before they actually get old). There's a chance Progressive Graying might come to exist in gerbils too. We're going to need to call it G if it does.
Here's an example of such a colour change. My dog Blair, a Pyrenean Shepherd (aka Berger des Pyrenees) as a puppy and adult. As he grew up he turned gray.
In any case, there's a lot of work still to do for scientists with these genes, to prove what they really are and how they behave. The official name is whatever is established in published scientific literature. Right now, the old paper that called it G is still official. But in the expectation that these genes will turn out to be the same as underwhite in mice, it has become common to use the term underwhite.
Now that we know why we're using uwd instead of g, hopefully no one will get confused any more. The important thing is to know that uw gerbils also exist, but if you're guessing the colour of someone's new gerbil, uw is probably not involved.
uw(d): underwhite dense (aka g)
uw(d) has a number of effects on gerbils. First, it reduces the yellow or gold in the coat to a pale cream, creating the appearance of gray. You can see that in the gray agouti compared to the golden agouti, and silver nutmeg compared to nutmeg. And it slightly lightens the coat of a black to make it slate.
uwd's other effects are more subtle. It dilutes the eye colour just a bit so if you shine a light at the eye you can see a red tint or glow. They look somewhat red though they are black according to the genes. Normal black eyes look black no matter what you do with the lights.
And an important one is the toenails. On a solid colour gerbil, uwd lightens black toenails to brownish. That's the best way to tell if a gerbil is uw(d)uw(d) or not. But if the gerbil has white markings the toenails will be white and won't help at all!
You don't want to confuse the lightening effect of white markings with the lightening effect of uw(d) though. Razzle is pied black; the black is lightened by the white markings. Mina is slate. Pied slate would be even lighter because of Sp.
In gerbils with red eyes, the eyes will be red anyway because of pp. Where p has already lightened the coat to eliminate most of the black, uw(d) now lightens the orange for very pale gerbils indeed. Argente golden lightens to ivory cream. Red-eyed honey lightens to apricot.
* Note that the technically correct way to write it is uwd rather than uw(d). uw(d) (or even uwd) is easier to type though and tends to be used in unofficial writing as a result.
uw: underwhite (cream)
If gray agoutis and slates are uw(d), you're probably wondering where those uw gerbils are. Well, the mutation has turned up a number of times around the world in pet shop gerbils. But people didn't often breed them, and if they did they didn't do it for long. They have, however, been bred for many years by one breeder in the U.S. and in Singapore. But they are not generally available.
uwuw is a powerful combination. It strips almost all of the colour from even the darkest gerbils, as well as diluting black eyes to red (similar to how c(h) lightens black eyes to pink). Depending on the combination of genes involved, you end up with various shades of cream or satin. On pups you can see the reduced pigment even before the eyes open.
Add the e gene (ee uwuw P-) and cream turns to white. So that's a white gerbil with eyes that should be black but are dark red, thus are sometimes called "funky white." In Singapore this is called dark-eyed white. Gerbils that are uwuw pp already have red eyes, and since p also lightens the coat the gerbils will be white with red eyes.
Since this gene can produce very pale and white gerbils, this can become a problem as it can be hard to figure out just what colour a gerbil really is. And unfortunately, white gerbils with red eyes tend to not be very popular with humans.
Keep in mind that uwuw cream, without other genes lightening it, actually looks quite different from the various other colours also known as cream. uwuw cream has a gray tone while other creams have an orange tone.
Thanks to Singapore Gerbil Clan in Singapore for some of these pics. More pictures at Singapore Gerbil Clan.
uwis powerful even alone. It slightly lightens all colours it appears with. Since uw(d) is not completely dominant over uw, gerbils with uw(d)uw are slightly lighter than the equivalent uw(d)uw(d). A special case is the slate where it's called azure slate. It's quite pretty, and tends to take on a different appearance depending on the light (more so than other colours). In low light they look exactly like slates. They get lighter looking with more light, and can look like several different shades in mixed light.