The description bimetallic cats refers to a unique coat coloration. Bimetallic cats are flesh and blood not metal. The term currently relates mainly to Siberian cats, which are a pedigree cat that looks like a Maine Coon or Norwegian Forest Cat. All three may have the same ancestors. However, I think there are lots of random bred cats that are also bimetallic. At least they look it. Perhaps there has been little focus on moggies or perhaps I am wrong and Sarah Hartwell will scold me for writing that ;).
I am informed by Sarah Hartwell (thanks Sarah) that within some SIberian cat breeding programmes (lines) cats are popping up that have a golden-like “stain” of colour that appears to be laid over the existing tabby coat. When the tabby is a silver tabby, the effect is silver contrasted with gold, hence bimetallic Siberian cats. “Bimetallic” means two metals.
On certain occasions when the coat is suitable, adding golden blobs of colour can make the cat look like a tortoiseshell cat. Because tortoiseshell cats are almost always female, when a lot of male tortoiseshells turned up someone scratched their heads and asked questions.
It has now been decided that the bimetallic coat is due to a genetic mutation that was perhaps introduced into Siberian cat lines by a random bred (freeborn) foundation cat with which the pedigree cats were outcrossed perhaps to avoid inbreeding while improving the cat’s appearance.
What I mean by a “random bred foundation cat” is that all Siberian cats, Maine Coon cats and Norwegian Forest Cats are refined versions of the natural and original random bred cat (the moggie foundation cat) from Northeastern Europe and Russia (I suppose).
Within the current population of original Siberian cats there appears to be mutated gene that found its way to the cat fancy in America. I am not sure if the gene is recessive or dominant. I don’t think the experts know for sure but it seems to be a recessive gene brought out through line breeding. Recessive genes are often hidden and have no effect on the cat.
Here is photo of Lexus, a bi-metal Siberian cat of 11 weeks of age, from Facebook:
Below is a photo of a random bred tabby cat on Flickr. It looks to me like he is a bimetallic cat but no doubt there is some reason why he is not. Perhaps this is an example of rufinism, which is described as “the degree of expression of orange/yellow pigment”³.
With respect to bimetallic cats, the genetic effect called “rufism” (also called “rufinism”) has been ruled out because of the “degree and intensity” of the colour¹.
At the level of each hair strand the golden colour is due to a broader band of phaeomelanin which is yellow/red/orange pigment in the hair strands. Melanin (eumelanin) is dark brown and the other banded pigment. This how a classic tabby hair strand might appear:
If the phaeomelanin band is wider the hair will look more orange/yellow hence the golden colour of these bimetallic cats.
Refs: (1) Messybeast.com (2) Original photo of tabby random bred cat on Flickr (3) Robinson’s Genetics 4th edition.