C-Locus (Siamese and Burmese)

The Siamese and Burmese coat patterns are controlled by the gene TYR (tyrosinase) which produces an enzyme that is required for melanin production. The Burmese pattern is a result from reduced pigment production changing black pigment to sepia and orange to yellow. The Burmese points are darker than the body and the eyes are yellow-gray or yellow-green. The Siamese pattern shows reduced pigment production to the points and the eyes are blue. This gene is also known as Color gene or C-locus. The Coat Colour Siamese (K758) and Coat Colour Burmese (K759) combined reveal the genetic status of the C-locus. The C-locus has three variants (alleles). The C allele is dominant over the alleles cb and cs; allele cb is semi-dominant over allele cs. The dominant allele C does not have an effect on the coat colour. Two copies of the cb allele (homozygous cb/cb) results in a Burmese coat pattern. One copy of the allele cb and one copy of the allele cs (cb/cs) result in the intermediate mink colour. Two copies of the cs allele (cs/cs) results in a Siamese coat pattern.

The Coat Colour Siamese and Coat Colour Burmese tests (together C-locus) enclose the following results:

Siamese	Burmese	C-locus	Coat Colour
N/N	N/N	C/C	Full colour
N/N	N/cb	C/cb	Full colour
N/N	cb/cb	cb/cb	Burmese / Sepia
N/cs	N/N	C/cs	Full colour
N/cs	N/cb	cb/cs	Tonkinese / Mink
cs/cs	N/N	cs/cs	Siamese / Pointed

In the following scheme the results of the C-locus are shown in combination with the possible results for the B-locus and D-locus:

C-Locus	B-locus	D-locus	Coat Colour
C/C	B/B, B/b or B/b’	D/D or D/d	Black
C/C	B/B, B/b or B/b’	d/d	Blue
C/C	b/b or b/b’	D/D or D/d	Brown, chocolate
C/C	b/b or b/b’	d/d	Lilac
C/C	b’/b’	D/D or D/d	Cinnamon, Red
C/C	b’/b’	d/d	Fawn
C/cb	B/B, B/b or B/b’	D/D or D/d	Black
C/cb	B/B, B/b or B/b’	d/d	Blue
C/cb	b/b or b/b’	D/D or D/d	Brown, chocolate
C/cb	b/b or b/b’	d/d	Lilac
C/cb	b’/b’	D/D or D/d	Cinnamon, Red
C/cb	b’/b’	d/d	Fawn
C/cs	B/B, B/b or B/b’	D/D or D/d	Black
C/cs	B/B, B/b or B/b’	d/d	Blue
C/cs	b/b or b/b’	D/D or D/d	Brown, chocolate
C/cs	b/b or b/b’	d/d	Lilac
C/cs	b’/b’	D/D or D/d	Cinnamon, Red
C/cs	b’/b’	d/d	Fawn
cb/cb	B/B, B/b or B/b’	D/D or D/d	Sable, Seal Sepia
cb/cb	B/B, B/b or B/b’	d/d	Blue Sepia
cb/cb	b/b or b/b’	D/D or D/d	Chocolate Sepia, Champagne
cb/cb	b/b or b/b’	d/d	Lilac Sepia, Platinum
cb/cb	b’/b’	D/D or D/d	Cinnamon Sepia
cb/cb	b’/b’	d/d	Fawn Sepia
cb/cs	B/B, B/b or B/b’	D/D or D/d	Seal Mink, Natural Mink
cb/cs	B/B, B/b or B/b’	d/d	Blue Mink
cb/cs	b/b or b/b’	D/D or D/d	Chocolate Mink, Champagne Mink
cb/cs	b/b or b/b’	d/d	Lilac Mink, Platinum Mink
cb/cs	b’/b’	D/D or D/d	Cinnamon Mink, Honey Mink
cb/cs	b’/b’	d/d	Fawn Mink
cs/cs	B/B, B/b or B/b’	D/D or D/d	Seal Point
cs/cs	B/B, B/b or B/b’	d/d	Blue Point
cs/cs	b/b or b/b’	D/D or D/d	Chocolate Point
cs/cs	b/b or b/b’	d/d	Lilac Point, Platinum Point
cs/cs	b’/b’	D/D or D/d	Cinnamon Point
cs/cs	b’/b’	d/d	Fawn Point