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On the picture above you can see the Mongolian gerbil's chromosomes, on these chromosomes all the genes, including the colour genes, are located.
BASIC COLOUR GENETICS
Before I will name the different genes, first something about basic colour genetics.
At this moment there are 6 different genes known that contribute to the colour of the gerbil. The combination of these genes determine the appearance of the animal. Genes occur in pairs, one gene comes from the mother, the other comes from the father. These genes are reflected as letters. The letter indicates what locus, this is the place on a gene, is mentioned. A capital points out that the gene is dominant, a small letter means the gene is recessive. Dominant genes have a stronger effect than recessive genes. If there is one dominant gene, and one recessive gene, than the dominant gene will overrule the recessive gene, and determine the appearance. A recessive gene will occur in the appearance only when there are two recessive genes present.
For instance the A locus. Having the A gene means that the animal has the agouti colour, while the a gene causes the black colour. Because A is dominant over a, an animal that has Aa will be agouti, like an animal with AA. Only an animal with aa will be black. When you see an agouti gerbil, the animal can thus be Aa or AA, that is written as A-. The - means that you don’t know if there is an A or an a present.
There are two different genes that can lead to red (also called pink) eyes. First there is the p gene (pink eyed dilution), pp leads to animals with red (pink) eyes, and pp also dilutes the coat colour; black (aaC-P-) turns to lilac (aaCCpp) and agouti (A-C-P-) turns to argente golden (A-CCpp).
Then there is the himalayan gene (c[h]), which leads to (almost) white animals with red (pink) eyes.
Depending on the other genes you can have Dark Tailed White animals with, as the name says, a dark tail, from vary dark brown (aac[h]c[h]P-, black background) to only a few dark hairs (A-c[h]c[h]P-, agouti background).
When the c[h] and p come together, you get so called "mock albino's", animals that are completely white, looking like true albino's (--c[h]c[h]pp, lilac or argente background).
There will be some very light coloured lilac or argente hairs in these tails, but you won't see them, that's why they look completely white.
Now about the doves and argente cream, because there is something strange going on.
Normally an animal with only one c[h] does not look different than an animal with CC, because C is dominant over c[h]. But there is an exception, when there are two p's present. Then the one c[h] does effect the coat colour!
So:
aaCCpp = lilac
aaCc[h]pp = dove
A-CCpp = argente golden
A-Cc[h]pp = argente cream
The one c[h] is able to lighten up the coat colour.
This is called dominance modification. The dominating effect of the C over c[h] is modified by pp.
GENES
There are 7 known genes that determine the colour of the Mongolian gerbil:
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GENE
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COLOUR EFFECT
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Agouti gene
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AA or Aa leads to agouti coloured animals (with a light coloured belly)
aa gives self coloured animals (without a light coloured belly)
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Dilution gene
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DD or Dd leads to normal coloured animals.
dd dilutes the original colour (black to blue), because pigment will clot.
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Pink eyed gene
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PP or Pp leads to black eyes
pp leads to red (pink) eyes and a lighter coat colour
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Grey factor gene
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GG or Gg leads to animals with yellow pigment
gg reduces the yellow pigment to white, but it also affects the black pigment
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Himalayan/Burmese gene
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CC leads to fully coloured animals
Cc[h] , in combination with pp, leads to a lighter coat colour
c[h]c[h] leads to white animals which can have a dark tail. On this gene, there is probably a third mutation, that leads to the Burmese and Siamese: c[b]
Cc[b] leads to normal coloured animals
c[b]c[b] leads to the Burmese pattern
c[b]c[h] leads to the Siamese pattern
Both the c[h] and the c[b] mutation cause acromelanism, which means that the body is lighter and the extremities like nose, ears, tail and feet are darker coloured.
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Extension gene
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EE and Ee leads to normal coloured animals
ee makes the bluish grey hair base of the agouti animal yellow
Combined with aa, ee leads to a dark agouti animal, without the light belly
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Spotting gene
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Spsp leads to spotted animals (white spots at nose, head, neck, white belly, feet and white tuft on tail)
spsp leads to non-spotted animals
SpSp animals die before birth
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Recently a new coat colour gene has been discovered, producing a true blue gerbil.
Most likely this gene is the dilution gene d, already known in mice and rats.
This gene can dilute colours, leading to dilute agouti's, the dilute black is called blue, leading to a dark grey/bluish colour, with slightly diluted eyes.
Currently people from the Gerbil Genetics Group are outcrossing some dilute carrying animals, to confirm that this is indeed the dilute gene, and to make sure there are no other defects attached to this new mutation. And to see how this gene interacts with the other, known, genes.
See pictures and comments on this new gene here.
Next is a table, with all the genes, summarized.
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DOMINANT
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RECESSIVE
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A = agouti
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a = self coloured (non-agouti)
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D = normal coloured
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d = dilution of colour
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P = dark eyes
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p = red (pink) eyes (also dilutes the coat colour)
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G = yellow coloured
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g = grey coloured (yellow turns into white)
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C = fully coloured
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c[h] = Himalayan (turns hairs at body white)
c[b] = Burmese pattern
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E = fully coloured
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e = yellowing gene
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Sp = spotted
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Sp = spotted sp = non spotted
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In the following gene chart you can see how most colours look, genetically:
(not all combinations are listed, some of them have no name yet, or look so much like other colours, that they don't have a separate name). The dilute gene is also left out, because not all combinations are known yet.
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COLOUR
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GENES
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A
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C
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E
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G
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P
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golden agouti
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A-
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C-
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E-
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G-
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P-
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argente golden
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A-
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CC
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E-
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G-
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pp
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argente cream
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A-
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Cc[h]
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E-
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G-
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pp
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black
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aa
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C-
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E-
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G-
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P-
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lilac
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aa
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CC
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E-
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G-
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pp
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dove
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aa
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Cc[h]
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E-
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G-
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pp
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dark tailed white
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--
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c[h]c[h]
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E-
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--
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P-
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pink eyed white
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--
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c[h]c[h]
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--
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--
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pp
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grey agouti
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A-
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C-
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E-
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gg
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P-
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slate
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aa
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C-
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E-
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gg
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P-
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ruby eyed white
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aa
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CC
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E-
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gg
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pp
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ivory cream
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A-
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CC
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E-
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gg
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pp
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ivory cream (light)
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A-
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Cc[h]
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E-
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gg
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pp
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sooty yellow (dark eyed honey)
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A-
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CC
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ee
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G-
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P-
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nutmeg
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aa
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CC
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ee
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G-
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P-
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polarfox
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A-
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CC
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ee
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gg
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P-
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yellow fox
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A-
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CC
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ee
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G-
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pp
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apricot
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A-
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CC
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ee
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gg
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pp
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silver nutmeg
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aa
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CC
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ee
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gg
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P-
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argente nutmeg
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aa
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CC
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ee
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G-
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pp
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colourpoint black (burmese)
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aa
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c[b]c[b]
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E-
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G-
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P-
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light colourpoint black (siamese)
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aa
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c[b]c[h]
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E-
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G-
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P-
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colourpoint agouti
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A-
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c[b]c[b]
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E-
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G-
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P-
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light colourpoint agouti
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A-
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c[b]c[h]
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E-
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G-
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P-
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colourpoint gray agouti
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A-
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c[b]c[b]
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E-
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gg
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P-
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colourpoint slate
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aa
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c[b]c[b]
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E-
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gg
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P-
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sapphire
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aa
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Cc[b]
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E-
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G-
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pp
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topaz
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A-
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Cc[b]
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E-
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G-
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pp
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schimmel
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--
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CC
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e[f]e[f]
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G-
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P-
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red eyed schimmel
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--
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CC
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e[f]e[f]
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G-
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pp
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champagne
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spotted schimmel
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To make this chart not to complicated, I left out the spotting gene. Spots are possible in all colours. The animal has the genetic formula for that type of colour, plus Spsp. The Sp gene does lighten up the colour. In white animals you can not see the white spots. Although in dark tailed white animals, you can see the white tuft on the dark tail.
An even more complete list of names and genotypes can be found here.
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