White, Tortoiseshell, Color-point, Chimera, Merle (what we know) Explained

  • Cats with N/Ws genotype will have white spotting. They will transmit this white spotting variant to 50% of their offspring, and those offspring are expected to be white-spotted.

  • Cats with Ws/Ws genotype will have white spotting. They will transmit this white spotting variant to all of their offspring, and all of their offspring are expected to have white spotting.

  • Cats with DW/Ws genotype will be white and may have some degree of hearing impairment. They will transmit a dominant white variant to 50% of their offspring and a white spotting variant to 50% of their offspring.

  • Alleles: N = Normal or non-white, DW = Dominant white, Ws = White spotting

  • Cats with N/N genoytpe are not expected to be white (in the absence of albinism) and cannot transmit a dominant white or white spotting variant to their offspring.

  • Cats with N/DW genotype will be white and may have some degree of hearing impairment. They will transmit this dominant white variant to 50% of their offspring, and those offspring are expected to be white.

  • Cats with DW/DW genotype will be white and are likely to have some degree of hearing impairment. They will transmit this dominant white variant to all of their offspring, and all of their offspring are expected to be white.

  • Depigmentation gives the red-eye with camera's flash.

  • There is also a gene(s) for blue eyes which is inherited separately from coat color.

  • Sometimes bi-color cats with white faces have blue eyes.

  • Not all blue-eyed cats are white, nor are all blue-eyed non-white cats "Ojos Azules". The blue-eyed trait turns up surprisingly often in random-breeding cats.

  • There are various known & unknown genes involved in white spotting & in blue-eyes

  • There is an established link between the white coat color, blue eyes & deafness, HOWEVER, this only pertains to specific genes.

  • There are five "known" alleles for albinism: blue-eyed albino ("ca"), pink-eyed albino ("c"), Burmese pattern ("cb"), Siamese pattern ("cs")and full color (non-albino, "C").

Male tortoiseshells are rare!
A tortoiseshell, or torties for short, are a combination of two colors other than white, either closely mixed or in larger patches.

The primary gene (B) for the colors brown, chocolate, cinnamon, etc., can be masked by the co-dominant gene for the orange color (O) which is on the X Chromosome.
It has two alleles, the orange (X
O) and not-orange (Xo), that produce orange phaeomelanin and black eumelanin pigments. The tortoiseshell and calico cats are indicated: Oo to indicate they are heterozygous on the O gene. The (B) and (O) genes can be further modified by a recessive dilute gene (dd) which softens the colors. Orange becomes cream, black becomes gray, etc. Various terms are used for specific colors.

"Normal" tortoiseshells have patches of black and red. The nose and paw-pads may be mottled between black and pink.

"Chocolate torties are patched with chocolate and red. The nose and paw-pads may be mottled between chocolate and pink."

"Cinnamon torties are patched cinnamon and red. The nose and paw-pads may be mottled between cinnamon and pink."

"Dilute tortiess are blue and cream. The nose and paw-pads may be mottled blue and pink."

"Lilac torties are lilac and cream. The nose and paw-pads may be mottled lilac and pink."

"Fawn tortoiseshells are fawn and cream. The nose and paw-pads may be mottled brownish-pink and pink."

"Caramel torties are caramel and apricot. The nose and paw-pads may be mottled caramel and pink."

Colourpoints

There are 3 levels of colour-pointing seen in cats. These are all due to temperature dependent albinism genes that cause cooler parts of the body to develop darker pigment. The first is the familiar high-contrast "Siamese" pattern known to geneticists as colourpoint or Himalayan pattern. The second is the low-contrast Burmese colour restriction, often referred to as sepia pointing (because it was first seen in brown/sepia Burmese). Intermediate between these is the mink pattern (Tonkinese colour restriction) caused when the Siamese and Burmese colour restriction genes interact.

The points may be solid, tabby or tortie colours. With Siamese colour restriction the torso is a shade of cream or ivory although some cats show "breakthrough markings" especially as they age. With Burmese colour restriction, the torso is marked with a slightly paler version of the colour and pattern. With Mink, the level of colour/pattern displayed on the torso is intermediate between those extremes.

The C Locus involves a master gene for pigment formation. When the gene is active, both black and yellow pigments can be formed. When the gene is mutated and not active, no pigment is formed. A recessive mutation at the C Locus will give a white (albino)

Chimera Pattern

A chimera is the result of 2 fertilized eggs fusing to become a single kitten. If the two fertilized eggs are both XY, this gives an XY/XY male chimera. In an XY/XY chimera if one X has the O gene and the other does not then some fur will be ginger and some black because different parts of the skin originate from different eggs! It could also be a mix of any other colors found in male cats e.g. a mosaic of blue (grey) and black. An XY/XY chimera would be fully fertile.

Female cats can also be chimeras, but they are generally only noticed if they have a "genetically impossible" mix of colors in the coat e.g. a mix of black and blue (grey) patches. Female chimeras can be XX/XX (two fused female embryos) or XX/XY (where the XX embryo cells form the gonads, producing a cat that appears physically female).

In mammals, chimeras are usually only identified when there is a mismatch between the chromosomal sex (XX or XY) and the genitalia. This can come about through investigation of an illness or through visual clues such as tortoiseshell coats in male cats.

If an XY egg fuses with an XX egg (a male embryo fuses with a female embryo), it gives a XX/XY chimera containing some tissues/organs which are genetically female and other tissues which are genetically male. In an XX/XY chimera, X chromosome inactivation will occur. The three X chromosomes in the animal may contain an assortment of different color genes (especially if the mother mated several times and the eggs were fertilized by different fathers). The physical appearance and the sexual behavior of an XX/XY chimera depends on which structures contain which chromosomes.

Merle

This gene has not yet been identified in felines, but is found in dogs. We're currently still searching for the gene to better understand the communication between genes. Broadly speaking it manifests as patches of dense color on the equivalent dilute e.g. black patches on a blue background, black patches on caramel, red patches on cream. This is different from tortie where the patches are a mix of a black-based color with a red-based color. The only instances of this phenotype in cats have been chimeras where one cell line has the dense color (e.g. black) and the other has the corresponding dilute color (e.g. blue). Theoretically it could combine with existing colors and patterns, but would only show to good effect on dilute-coated cats e.g. a blue/cream tortie with black patches, or a lavender (lilac) tabby with chocolate patches. Theoretically these could also be combined white spotting, colourpointing and silver/golden series. The chart shows how merle might manifest in cats should the mutation occur.