S locus — white spotting
Controls: White patches — from a locket or 'tuxedo' up to a mostly-white van.
White spotting adds unpigmented (white) areas on top of whatever colour the cat already is. It is dose-sensitive: a low grade gives a locket, white toes or a bib; more gives a bicolour or tuxedo; a high grade gives van and harlequin (white with a few coloured patches). This is DIFFERENT from dominant white (W), which turns the whole cat white.
Alleles
SWhite spottingDominantsNo spottingRecessiveBreeding examples
Bicolour (S/s) × No white (s/s)
← ≈ half the kittens show some white, half none — the amount then varies.
High-white van × High-white van
← Kittens tend to carry a lot of white too (two doses push the grade up).
Colours it produces
Frequently asked questions
What is the difference between white spotting (S) and dominant white (W)?+
White spotting (S) adds white PATCHES to a coloured cat (tuxedo, bicolour, van). Dominant white (W) masks the ENTIRE coat so the cat is all white. They are separate genes.
What is a tuxedo cat?+
A low-grade bicolour: mostly coloured with a white chest, belly and paws — like a cat wearing a dinner suit.
A calico is a tortie with white — how does that work?+
A calico is a tortoiseshell (red + black patches) PLUS white spotting. The white breaks the mixed colour into clear, separate patches.
Are white cats more likely to be deaf?+
It is a well-documented genetic association: dominant white (W) — and high white spotting near the head — is linked to congenital deafness, most in blue-eyed white cats. Many breeders account for it in their pairings.
Related genes
See these colours on real cats.
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