The MFSD12 gene, also known as I-Locus affects the expression of the pheomelanin (red) pigment. The MFSD12 gene has no effect on eumelanin (black) pigment, therefore the black coat and the black hair ends remain black. The mutation affects the pheomelanin in the entire coat resulting in a pure white or cream coat colour. The pigmentation of the nose, lips, eyes and skin remains unchanged. The intensity of the dilution may differ in various dog breeds. The Coat Colour I-Locus test (H821) tests for the genetic status of the I-Locus. The I-Locus has two variants (alleles). The allele I is dominant and does not have an effect on the coat colour. Only when the dog has two copies of the recessive allele i the coat colour is diluted.
The Coat Colour I-Locus test encloses the following results, in this scheme the results of the Coat Colour I-Locus test are shown in combination with the possible results for the E-Locus and B-Locus:
| I-Locus | E-Locus | B-Locus | Coat Colour | Nose/foot pads |
|---|---|---|---|---|
| I/I | Em/Em, Em/E or Em/e | B/B or B/b | Black, melanistic mask is not visible | Black |
| I/I | Em/Em, Em/E or Em/e | b/b | Brown/chocolate/liver, with melanistic mask | Pink to Brown |
| I/I | E/E or E/e | B/B,B/b | Black, no melanistic mask | Black |
| I/I | E/E or E/e | b/b | Brown/chocolate/liver, no melanistic mask | Pink to Brown |
| I/I | e/e | B/B,B/b | Red/Yellow/Cream | Black |
| I/I | e/e | b/b | Red/Yellow/Cream | Pink to Brown |
| I/i | Em/Em, Em/E or Em/e | B/B or B/b | Black, melanistic mask is not visible | Black |
| I/i | Em/Em, Em/E or Em/e | b/b | Brown/chocolate/liver, with melanistic mask | Pink to Brown |
| I/i | E/E or E/e | B/B,B/b | Black, no melanistic mask | Black |
| I/i | E/E or E/e | b/b | Brown/chocolate/liver, no melanistic mask | Pink to Brown |
| I/i | e/e | B/B,B/b | Red/Yellow/Cream | Black |
| I/i | e/e | b/b | Red/Yellow/Cream | Pink to Brown |
| i/i | Em/Em, Em/E or Em/e | B/B or B/b | Black, melanistic mask is not visible | Black |
| i/i | Em/Em, Em/E or Em/e | b/b | Brown/chocolate/liver, with melanistic mask | Pink to Brown |
| i/i | E/E or E/e | B/B,B/b | Black, no melanistic mask | Black |
| i/i | E/E or E/e | b/b | Brown/chocolate/liver, no melanistic mask | Pink to Brown |
| i/i | e/e | B/B,B/b | Pure white/Cream | Black |
| i/i | e/e | b/b | Pure white/Cream | Pink to Brown |
