(This page is not quite complete and still under development)
Basic Cat colour genetics is quite simple (really!) just remember the basic rules! (OK-we are making some assumptions and simplifications!)
Rule 1:
All Siamese (and Ocicats) are basically either seal (tawny), chocolate or cinnamon. In all the cats in the world there are only 3 possible genes that control these colours. Any individual cat can only have 2 of these 3 possible genes, ie one from each parent. Explanation 1 and 2.
Rule 2:
All others colours come from effects of other genes on these basic colours. Explanation 3
Rule 3:
Some genes have a stronger effect than others (they are said to be dominant). However all colour genetic effects are "all or nothing" therefore the dominant gene always shows its colour over a weaker one (recessive). The colours don't merges to become a "half way" colour. (Dominant genes are always written in uppercase).
More detail is given under the following headings- I have tried to keep this easy to read so click on the links if you want more information or explanations.
Basic Patterns
Siamese pattern
Ocicat pattern
(Rule 1 and 3)
The gene for seal is called "B" it is a dominant gene. (B because the gene is really Black, the only confusion here is that cat breeders use much more sexy names such as Seal and Tawny)
The gene for Chocolate is called "b" it is weaker than B ie it is recessive to the black gene.
The gene for cinnamon is "bl" it is weaker than both B and b ie it is recessive to both of them.
So any cat will have 2 of these 3 possible genes therefore.
A seal is BB or Bb or Bbl. All these three cats look exactly the same you would only find out they were not all genetically the same when you breed them. (for those interested we say: the phenotype is identical but the genotype is different)
A Chocolate is bb or bbl. Again they look exactly the same.
A cinnamon can only be blbl.
Genes that effect the basic colours. (rule 2)
The first is the Dilute gene, D. The effect is "what it says" ie it dilutes the colour, so it turns:
Seal (tawny) to Blue
Chocolate to lilac
Cinnamon to fawn
D is the original gene and does not effect the basic colour, it is the recessive form ,d, that alters the colour. Therefore a cat that was DD or Dd will not be dilute, whereas one with dd will be.
A Dd cat "carries dilute" some breeders incorrectly use the term "carries blue" which is confusing especially when they are talking about a chocolate cat!
So I am sure go could now work out the genes for all the possible colours. Click here to see the possibilities
A controversial little gene in some cat breeds! It is not allowed in ocicats and in some countries it is not allowed in siamese.
Again it does what it says - that is it modifies the dilute colours. It changes the dilute colours to caramel. It has no effect on non dilute colours.
This is a dominant gene therefore a caramel cat could be DMDM or DMdm. Blues, lilacs and fawns must be dmdm. Remember it has no effect on non-dilutes so a seal is seal even if its got the DM gene.
The slight confusion here is that "caramel" actually is 3 different colours depending on the basic colour genetics. In USA they differentiate between blue based and lilac based caramel calling the later Taupes. Click here to see possible genotypes
Ok now we are getting a bit more complicated....... This bit dosen't apply to Ocicats.
The red gene is a sex linked gene. It also has a masking effect on other colours, which means that what ever other colour genes your cat carries if it also carries the red gene, O, then the cat will be a red series cat. Non-red series cats are oo. Click here for more information
The D and the DM gene have similar effects on the O gene as it does on the other colours, therefore:
Reds have genotypes O- with D-
Creams have genotypes O- with dd
Apricots have genotypes O- with dd and DM-
Silver gene is not relevant to the Siamese, however it was introduced into Ocicats by out-crossing to American Shorthairs. The silver gene is more correctly called the Inhibitor gene (I) it is a dominant gene. It is only truly silver in Tabby cats, self (non Tabbys) cats who express the gene are called Smokes. The inhibitor gene decreases the yellow pigment in the coat- this has the effect of whitening the background of the pattern (explanation). Tansy, a cinnamon silver (on the right below), exhibits this and when seen against her brother a cinnamon (left) the effect is obvious.
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In the beggining all cats were tabbies. The gene for Tabby marking is A, non-tabbies also called "Self" cats have the recessive form of the gene aa. The letter A is used to represent Agouti- this is a cellular protein that causes pigment changes in cells and thus allows the tabby pattern to be seen.
A tabby cat can be any of the colours already mentioned -including torties (giving tortie-tabbies sometimes called torbbies!)
A Tabby is therefore AA or Aa. Selfs are aa. Click here for more information. All Ocicats are tabbies and Siamese can be tabby.