E: Extension

Extension of yellow gives us many beautiful, fascinating colours. Not only does it change gerbil hair colour, it can also change the pattern it grows in and it can make gerbils change colour over time.

golden agouti hairsBut before we get into it, let's review golden agouti gerbil hair:.

Each hair has 3 parts:

  1. The part nearest the skin is the undercoat, and it's naturally gray.
  2. The part in the middle of the hair shaft is gold or yellow.
  3. The tips of the hairs are black.

These colours are all needed for golden agouti. The 3 colours blend together to make a gerbil that looks brown. This is dominant extension, E.

Extension comes in 3 varieties:



One of the cool effects of e is to extend the colour from the middle of the hair shaft all the way down to the skin, covering the dark undercoat and making it disappear. It could be orange, yellow or white, depending on the colour of the gerbil. Here's an example in red eyed gerbils:

E undercoat photo

Argente golden

A- E- pp

Argente golden is a regular E- colour with gray undercoat (lower part of each hair). You can see it if you make a part in the coat. There are no black tips on the hairs because pp has lightened them.

ee undercoat photo

Red-eyed honey (REH)

A- ee pp

Red-eyed honey is different from argente golden in that it has ee instead of E-. ee extends the orange to cover the gray undercoat so it goes all the way to the skin. The gray undercoat is gone. Again there are no black hair tips because they've been lightened by pp.


A- colours: Belly line

ee also extends light colours over other places that would otherwise be darker. In gerbils that have white bellies, ee makes the white belly extend over a bigger area: part way up the side of the gerbil's body.

Hemi is a golden agouti, E-. She has a brown back and sides, and has a white belly. Racy is a dark eyed honey (DEH), ee. She lacks the gray undercoat and the dark hair dips, turning her orange. And the white belly comes part way up the side of her body. The extended white also lightens the area around her eyes.

agouti white belly hard to see from the side DEH white belly comes up the side of the body

We see a similar effect on gerbils with red eyes.

Cherokee is argente golden, E- pp. He has a white belly, but you can barely see it from the side of his body. Rem is red eyed honey (REH), ee pp. He looks a lot like Cherokee but his white belly extends almost half-way up the side of his body. Easy to see from the side. I think of it as Gene, the painter, having to bring his extension ladder so he can paint the white up the side of the gerbil. pp has lightened the dark hair tips on the red eyed gerbils.ee argente white belly hard to see argente vs REH photo

Seeing the white belly going partway up the side of the body is a handy clue when you're trying to figure out what colour a gerbil is.

ee colours: Colour change

In other species, ee makes virtually all black disappear completely so the animal can only be some shade of yellow or orange or red. In gerbils this is only true in youngsters before their adult coat comes in. When hair first grows on young pups, ee extends the colour in the middle of the hair shaft so the hairs are yellow or orange. But even then there's areas with dark pigment and some black hair can show. When their adult coat comes in, more black shows up as it's able to overcome the power of ee. But only some of it. As ee gerbils age, some of that black can fade.

Gerbils molt, or change their hair, throughout their lives. Between 6 weeks and 10 weeks of age, the baby hair molts out and the adult coat grows in. The colour change is especially dramatic in ee gerbils. The new colour appears in a particular pattern across the body.

A- gerbils also molt to a different adult coat colour but the change is less dramatic.

Toby, silver nutmeg, molts:
Nutmeg gerbils change colour in the same way as silver nutmegs. The only difference is the background colour is orange instead of cream.
Nutmeg: aa C- ee P- Uw-
Silver nutmeg: aa C- ee P- uw(d)uw(d)


One of the really remarkable things about e is the great variation in the colours, more than with other genes. Here are just a few of the different shades of nutmeg:

shades of nutmeg shades of nutmeg shades of nutmeg

The dark nutmeg gerbil at the end is actually Cc(chm) ee. You might expect c(chm) to make the hair lighter but it didn't.


e(f): Fading (Schimmel)

There is a more extreme version of e called e(f). ee and e(f)e(f) pups look much the same. It can be hard to tell them apart, although e(f)e(f) pups often have a tiny white spot on their heads. e(f) has all the same effects as e. But it does something different as the gerbil grows up. As the gerbil molts into its adult coat, instead of more black showing up, e(f) causes the body hair to fade until it actually turns white. The tail keeps its orange colour. There's a wee bit of orange left around the nose while the ears are gray.

Here's Shimmer molting away her pretty orange baby coat on her way to becoming a beautiful adult schimmel.

schimmel molt schimmel molt

adult schimmel 

The shade of orange (pups and tails) varies depending on the other genes the gerbil has and natural variation. A- schimmels tend to be a lighter orange. aa schimmels are more likely to be a deeper shade of orange.

Spotted schimmel: e(f)e(f) Sp

Spotted schimmel is a special pattern sometimes called champagne. Pups start with just the faintest orange pied pattern regardless of whether it's actually spotted, pied or mottled. This fades away soon enough. The tail and nose amd ears keep their colour and may be gray or orange. The tip of the tail will be white since the gerbil is spotted.

champagne at 30 days champagne adult



e and e(f) are closely related genes. Pups are the same colour whether ee or e(f)e(f). But their effects on adult coats are quite different. So what happens when the two genes are together?

LDEH 1 year LDEH 2 1/2 years

Somehow these genes find a way to go halfway in between! In ee(f) gerbils the black tips that would normally appear in ee gerbils can't show up at all. Instead of fading when molting into the adult coat, ee(f) gerbils fade slowly with age. Eventually they can end up looking almost like schimmels.

ee(f) and spotting

ee(f) with white markings The white spotting gene interacts with ee(f) in a special way. The white belly might keep getting even higher. The orange on the gerbil's back blends into the white on the sides gradually. The effect might be described as "racing stripes." The body colour can fade quite a lot over time. In some cases it can eventually end up looking almost entirely white just like a real schimmel, especially if there are other lightening genes involved.

faded ee(f) Sp photoThe same effect happens if a gerbil is Cc(chm) ee Sp or Cc(h) ee Sp. You get a much lighter gerbil with extensive white markings in a racing stripes pattern. You can't tell if the gerbil would actually be spotted, pied or mottled because they all turn out much the same.

Because of this unusual spotting pattern these gerbils are sometimes called honey cream. It's a catch-all term to cover a variety of gene combinations because you can't tell what it really is by looking at it.

Next page: Uw locus (aka G)

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