E-Locus (Extension)

The Extension gene (MCR1 gene) controls the production of black and red pigment. In cats, shades of red color are determined by the dominant Orange gene (O-locus) located on the X chromosome. The genetic background of the O-Locus is still unknown. The Extension gene is also known as E-locus. The Coat Colour E locus, extension test (K639) tests for the genetic status of the E-locus. The E-locus has two variants (alleles). It is presumed that (almost) all cats are fixed for the dominant allele E, they have two copies of the dominant allele E and based on this gene alone could produce both red and black pigment. The recessive allele e results in kittens that are born with a black/brown tabby pattern (blue/apricot in dilute cats). As the kittens mature, the black/blue pigment is replaced by yellow resulting in the golden coat coloration seen in adult cats. Originally it was named X Colour, now it is called Amber. The recessive allele can be present in the Norwegian Forest cat and traces back to a single female ancestor from Norway born in 1981. Cats with two copies of the allele e only have the Amber Coat Colour when the dominant O allele at the O-locus is not present.

The Coat Colour E Locus, extension test encloses the following results, in this scheme the results of the Coat Colour E Locus, extension test are shown in combination with the possible results for the O-locus. For the O-locus no DNA test is available: