Colour inheritance in Sphynx cats: where do kittens’ colours come from?

Sphynx cats have colour too

The absence of a conventional coat does not mean an absence of colour. In Sphynx cats, colour is assessed mainly through skin pigmentation and any fine hair present. The same colour may look different from that of a densely coated cat: a black Sphynx need not resemble an intensely black shorthair.

Several traits combine to create a cat’s appearance. A cat may, for example, be blue, have white patches and also be mink. Base colour, dilution, white markings and point-type pigment restriction can occur together. The whole colour cannot therefore be explained by a single letter.

What is visible, and what does a cat ‘carry’?

Phenotype is the trait we can see, such as black colour. Genotype is the genetic information behind it. Two similar-looking cats may have different genotypes and therefore different possibilities for passing colours to their offspring.

A version of a gene is called an allele. In most examples discussed here, a cat has two alleles at a particular DNA location, one from its mother and one from its father. It passes one of them to each kitten. I discuss red separately because its inheritance is linked to the X sex chromosome.

If a cat has both a dominant and a recessive allele, the effect of the recessive allele may be hidden. We then say that the cat is a carrier, or ‘carries’ the trait. A black cat can therefore carry chocolate without being chocolate itself. ‘Dominant’ describes inheritance; it does not mean a better or more common colour.

Black, chocolate and cinnamon

The dark component of colour comes from a pigment called eumelanin. Depending on variants of the TYRP1 gene, described as the B locus, its effect may be black, chocolate or cinnamon. The dominance order is B > b > b^l: black is dominant over chocolate and cinnamon, and chocolate is dominant over cinnamon.[1]

Consider two black cats that both carry chocolate. Each is B/b. Either parent can pass B or b to a kitten.

In this simplified example, without dilution or other traits modifying visible colour, each kitten has a 75% chance of being black and a 25% chance of being chocolate. Half of the possible genotypes are black cats carrying chocolate.

Where do blue, lilac and cream come from?

The next element is colour dilution. It is associated with the MLPH gene, described as the D locus. It changes pigment distribution and makes the colour appear lighter.[2]

Dilution is expressed with the genotype d/d. A D/d cat is not dilute but can pass on the d allele. Two black cats carrying dilution can therefore produce blue kittens. Two d/d parents, in turn, pass d to all their offspring, so every kitten receives d/d.

Blue is dilute black, and lilac is dilute chocolate. A blue Sphynx may also carry chocolate: its genotype at these two locations might be B/b and d/d. One trait does not exclude the other.

Red and tortoiseshell: sex matters here

Red colour is associated with the production of pheomelanin, the pigment that produces yellowish and red shades. The red variant affects which pigment is produced in the cells. It does not turn existing black pigment into red pigment.[3]

Traditional notation uses the symbols O for red and o for non-red. This locus is on the X chromosome. Females usually have two X chromosomes, while males have X and Y. A male receives his X from his mother; a female receives one X from each parent.

A female with two O variants is red, while one with two o variants is non-red. The combination O/o produces tortoiseshell. During early development, one X chromosome is silenced in each cell. The O variant is therefore active in some areas of skin and o in others, producing a mosaic of red and non-red areas.[3]

The non-red areas may be black, chocolate or cinnamon. If d/d dilution is also present, these colours lighten too: black tortoiseshell becomes blue-cream, and chocolate tortoiseshell becomes lilac-cream.

A male with the typical XY combination has only one copy of this locus on his X, so he is usually either red or non-red. Tortoiseshell males are rare exceptions, associated with factors such as an unusual chromosome combination or chimerism.

This example assumes typical sex chromosomes, a black base for the non-red colour, and no dilution or other traits affecting visible colour.

It is not true that a male inherits his entire colour only from his mother. He receives the X chromosome carrying information about red from his mother. The other colour genes discussed here are inherited from both parents.

Point, mink and sepia: three different combinations

Alongside pigment type and dilution, where pigment is produced also matters. Point, mink and sepia are associated with variants of the TYR gene, described as the C locus. Pigment production is temperature-dependent to varying degrees: cooler parts of the body may be darker than the torso.[4]

The dash in C/– means that the second allele is not specified here. A cat may be C/C, C/c^b or C/c^s. The presence of C is sufficient to prevent pigment restriction from this locus being visible. A cat without visible points can therefore pass on a c^b or c^s.

Thus, two C/c^s parents can produce point kittens. Each kitten has a 25% chance of receiving c^s from both parents. Two C/C cats, however, cannot pass on either of these alleles.

Mink is the combination of c^b and c^s. When both parents are mink, three outcomes are possible:

When a sepia c^b/c^b cat is paired with a point c^s/c^s cat, all kittens receive c^b/c^s, the mink genotype. This still does not determine their base colour: they may differ, for example, in black, chocolate or dilution.

These examples concern the three alleles listed. They do not cover rare albinism variants or situations in which other genes mask the visible colour.

Does eye colour prove that a cat is mink?

Eye colour can be a clue, but it does not replace genetic testing. Blue eyes are typical of points, while mink eyes are often described as aquamarine. In practice, judging the shade can be difficult, especially in photographs.

Nor should every sepia be assumed to have identical golden eyes. More factors influence the shade than the c^b/c^b combination alone. Blue eyes can also have other causes, including white colour or variants associated with DBE. If in doubt, check the specific DNA result rather than determining genotype solely from the iris.

White can conceal colour

An entirely white colour and white patches are not the same thing. Dominant white can mask the effects of genes responsible for other colours. A white cat still has those genes and can pass them to its offspring. Appearance alone cannot reveal which colour is hidden beneath the white.[5]

White markings, by contrast, leave coloured areas visible. A Sphynx may be black and white, blue and white or tortoiseshell and white, for example. The size and distribution of patches are not a simple copy of the parents’ patterns: a small white spot on one cat cannot predict exactly how much white its kittens will have.

Unpigmented areas often look pink in hairless cats. This is one reason to describe colour by examining the whole cat, its development and test results, rather than relying on a single photograph.

What about tabby?

Genes affecting tabby patterns also act in Sphynx cats, although the lack of a conventional coat makes the pattern harder to interpret. One important element is the A locus, or agouti. In simplified terms, A allows agouti colour to be expressed, while a/a usually produces solid colour in non-red areas.[6]

With red and cream, the situation is less straightforward: stripes can also be visible in an a/a cat. Therefore, stripes on a red cat alone do not prove that it has an A allele.

In FIFe, tabby in Sphynx cats is recorded using the general code 21, without distinguishing specific pattern types. Silver and golden designations are also not used in this breed’s standard. These are rules for describing and registering colour, not proof that a Sphynx cannot have gene variants affecting those traits.[7]

One litter, four colours

Now combine two traits discussed above. A blue male carries chocolate, and a chocolate female carries dilution. Their genotypes are B/b d/d and b/b D/d. We assume that no other traits affect visible colour.

The male can pass B or b, but always passes d. The female always passes b, while at the other locus she can pass D or d. This gives four equally likely combinations:

This does not mean that all four colours must appear in a litter. It does show why ‘a blue father and a chocolate mother’ is insufficient information without knowing what they carry.

What can DNA tests reveal, and what cannot an EMS code tell you?

An EMS code records the registered colour. It does not contain a cat’s full genetic information and usually does not reveal which hidden alleles it may pass to its offspring. A blue cat carrying chocolate and a blue cat that does not carry it may have the same colour code.

A pedigree helps predict carrier status, but relies on correctly recorded ancestral colours. DNA testing checks specific variants without guessing from appearance. Read the panel’s scope carefully: the result concerns the variants actually tested, not every possible cause of that appearance.

At Aggio Cat*PL, I test all my breeding cats with the full Wisdom Panel / MyCatDNA feline genetic panel. I also use information about colour and carrier status to better understand the outcomes of pairings. Kittens’ colours can be predicted from their parents’ genes, but the exact composition of a particular litter cannot be ordered.