A primer on cat genetics
Updated with findings from molecular genetics research (2007–2024).
Classic reference: Roy Robinson – Genetics for Cat Breeders (1991).
Introduction
This article addresses the question "what colour is my cat, and what colours can my kittens have?" It covers colour terminology and how genes interact. Since Robinson's classic text (1991), molecular research has identified many new genes and confirmed previously theoretical ones.
Basic concepts
Chromosomes and genes. Every characteristic of a cat is determined by genes on chromosomes. Cats have 19 pairs of chromosomes (38 in total). Each characteristic is described twice – one gene from the mother, one from the father. When two gene variants (alleles) give different instructions, the dominant allele wins. The recessive allele is only expressed when present twice.
The genes
A – Agouti
The A gene determines whether a tabby pattern is visible. A–: agouti background colour with yellow/brown banding on hairs; tabby pattern visible. aa: yellow bands absent; the dark background masks the tabby pattern (solid colour). Agouti is dominant over non-agouti.
B – Black / Chocolate / Cinnamon
The B locus determines the intensity of eumelanin. Three alleles in dominance order: B (black) > b (chocolate) > bl (cinnamon). The dilute equivalent of cinnamon is fawn.
D – Dense / Dilute
D–: pigment evenly distributed → full colour. dd: pigment clumped → dilute colour: black becomes blue, chocolate becomes lilac, cinnamon becomes fawn, red becomes cream. Molecular gene: MLPH (melanophilin).
Dm – Dilute Modifier (new insight)
In some dilute (dd) cats, the Dm gene further modifies colour: blue becomes caramel and cream becomes apricot. Dm is dominant and only acts on dd cats. Recognised by TICA.
C – Colorpoint / Albino series
The C locus (Tyrosinase gene, TYR) controls total melanin levels. Dominance order: C > cb (Burmese) > cs (Siamese) > ca > c (pink-eyed albino). Colour restriction is temperature-sensitive: the cooler extremities (ears, muzzle, paws, tail) become darker.
I – Inhibitor / Silver
The I gene inhibits phaeomelanin production at the hair root. I–: white or silvery hair root with a coloured tip. Results range from smoke (minimal inhibition) to chinchilla (maximum inhibition). I is dominant over i.
Golden / Wide Band (Wb)
The golden colour (warm golden background instead of silver) was classically attributed to a theoretical Wide Band (Wb) gene. Recent research (2021–2024) suggests involvement of variants near the ASIP gene or modifier genes. The exact mechanism remains under investigation.
O – Orange (Red)
Sex-linked (X chromosome). O: converts eumelanin to phaeomelanin → orange/red coat. Females: OO = red, Oo = tortoiseshell, oo = non-red. Males: O = red, o = non-red. Tortoiseshell (Oo) females have random orange and non-orange patches due to X-inactivation (lyonisation). O with dd gives cream; tortie with dd gives blue-cream.
E – Extension / Amber (discovered after 1991)
A recessive mutation ea in the MC1R gene was found in the Norwegian Forest Cat (and LaPerm). It converts all eumelanin to phaeomelanin → amber colour, distinct from the Orange (O) gene. Kittens are born dark and lighten gradually. The dilute version is light amber.
S – Piebald Spotting / White spots
The S gene (linked to KIT) causes white patches and is dominant. Patterns: mitted (white paws), bicolour, harlequin, van (almost entirely white).
W – Dominant White
An allele of the KIT gene. Ww: entirely white coat; underlying colour masked but still transmitted to offspring. WW is usually lethal in the embryo. Blue eyes in white cats correlate with a higher prevalence of deafness.
T – Tabby pattern (Taqpep gene, 2012)
Tabby patterns are determined by the Taqpep gene (Kaelin et al., 2012, Science). Three alleles: Ta (ticked/Abyssinian, dominant) > T (mackerel) > tb (blotched/classic, recessive). Spotted tabby is a modification of mackerel, not a separate allele.
L – Longhair / Shorthair (FGF5 gene, 2007)
Shorthair (L) is dominant over longhair (l). Gene: FGF5. Multiple distinct recessive l alleles exist, each causing slightly different coat lengths.
Summary table
| Gene | Molecular gene | Effect | New after 1991? |
|---|---|---|---|
| A | ASIP | Agouti / solid | Confirmed |
| B | TYRP1 | Black / chocolate / cinnamon | Confirmed |
| D | MLPH | Full / dilute colour | Confirmed |
| Dm | Unknown | Caramel / apricot (if dd) | Yes – recognised by TICA |
| C | TYR | Colorpoint | Confirmed |
| I | Unknown | Silver / smoke / chinchilla | – |
| O | X chromosome | Red / tortoiseshell | Confirmed |
| E / Amber | MC1R | Amber (NFC, LaPerm) | Yes – 2007–2009 |
| S | KIT | White spots | Confirmed |
| W | KIT | Dominant white | Confirmed |
| T | Taqpep | Mackerel / blotched / ticked | Yes – 2012 |
| L | FGF5 | Short / long hair | Yes – multiple alleles (2007) |
References: Roy Robinson – Genetics for Cat Breeders (1991) • Kaelin WG et al. – Science 337 (2012) • Peterschmitt M et al. – Anim Genet 40 (2009) • Drögemüller C et al. – Science 316 (2007) • UC Davis Veterinary Genetics Laboratory • TICA Genetics Committee.