Cat Coat color – E locus (Extension/Amber)
On the E locus, the extension gene (symbol E) controls the production of red and black pigment.The name extension locus comes from the effect of black or brown pigment not being extended throughout the whole coat, but being restricted to the skin of the extremities and to the eyes. The dominant allele E on E locus produces black pigment in the coat while the recessive allele e produces red pigment and is due to a recessive mutation in the MC1R gene. The amber colour, initially called X-Colour, was officially reported in 1992 in the Norwegian Forest Cat (NFC) population and was never documented in other feline breeds. All amber cats have descended from a single ancestor, Kløfterhagens Babuschka, born in Norway in 1981, and this dame transmitted the amber trait to three daughters. Amber NFC genealogies show that non-amber cats can father amber kittens and amber matings only give amber kittens. There is no correlation between amber inheritance and the sex, supporting this colour as an autosomal recessive trait.
Peterschmitt, M., Grain, F., Arnaud, B., Deléage, G., and Lambert, V. (2009). Mutation in the melanocortin 1 receptor is associated with amber colour in the Norwegian Forest Cat. Anim. Genet. 40, 547–552.