Black Vs. Orange: Coat Color Dominance In Cats

The colour of a cat's coat is determined by its genetics. All cats originate from two colours: orange and black. The orange gene is carried on the X chromosome, which means that males—who have one X and one Y chromosome—will be either black or orange. Females, on the other hand, have two X chromosomes, and can therefore be either black, orange, or a combination of the two. This combination of black and orange is known as tortoiseshell, and it is very rare for males to have this colouring.

The genetics of cat coat colours

The colour of a cat's coat is determined by its genetics, which can get complicated. However, the basic principles are simple enough. Firstly, all cats originate from two colours: orange and black. The orange gene is just orange (O), while the black gene (B) has recessive versions, which cause a cat to be chocolate (b) or cinnamon (b').

The Dilute Gene

The dilute gene (d) lightens a cat's colour. It is recessive, so it must be inherited from both parents to be represented. The dilute gene turns:

• Orange to cream/buff
• Black to grey/blue
• Chocolate to lilac/lavender
• Cinnamon to fawn/light lilac

Sex-Linked Genes

The orange colour gene is only carried on the X chromosome, which is why 80% of ginger cats are male. Females, with their two X chromosomes, need to inherit the orange gene from both parents to be ginger, whereas males only need to inherit it from their mother.

Tortoiseshell and Calico

Female cats can have patches of orange and black fur, resulting in a tortoiseshell or calico cat. This is because they have one orange gene on one X chromosome and a black gene on the other. Male tortoiseshell or calico cats are rare and usually sterile, with chromosomal abnormalities.

White Cats

White cats are not albino, which is the absence of pigment. White cats have less melanin than other cats, but their genetics still contain colour. Solid white cats have the dominant white gene (W), which masks the cat's actual colour.

Tabby Cats

The A gene is responsible for patterns on cats. A cat with the dominant A gene will have a tabby pattern, while a cat with the recessive a gene will have a solid-coloured hair. All orange cats are tabbies, because the orange gene masks the solid gene.

The dominant and recessive genes

To begin with, the two fundamental colours in cats are black and orange (also known as red). The gene for black (B/b/b1) results in black fur when a cat possesses the dominant version of this gene (B). On the other hand, the gene for orange (O/o) leads to orange fur when the dominant version of the orange gene (O) is present. These two basic colours form the foundation for all other coat colours in cats.

The black and orange genes can also be influenced by other genes, creating diluted colours. For instance, the dense/dilute pigment gene (D/d) affects the deposition of pigment, resulting in diluted colours such as silver, grey, blue, cream, and fawn. The interaction of these genes leads to a variety of coat colours.

In addition to the dominant and recessive genes influencing the primary coat colours, there are other factors at play as well. For example, white spotting, which can be present in various amounts, is determined by the KIT gene. This gene controls the presence and extent of white in a cat's coat, ranging from small spots of white to mostly white patterns like the Turkish Van.

Furthermore, the topic of coat patterns adds another layer of complexity. The agouti gene, with its dominant (A) and recessive (a) alleles, plays a significant role in creating tabby patterns. The dominant allele results in the banding of colours on the hair shaft, leading to the typical tabby pattern. The recessive allele, on the other hand, creates a solid-coloured hair.

The interplay between the dominant and recessive genes, along with other genetic factors, gives rise to the diverse array of coat colours and patterns observed in cats. While the underlying genetics can be intricate, the resulting combinations of colours and patterns are fascinating to observe and appreciate.

The role of the X chromosome

The X chromosome plays a significant role in determining a cat's coat colour. The gene for the colour orange is located on the X chromosome. This means that male cats, with their XY combination, only need to inherit the gene for orange once to have an orange coat. In contrast, female cats, with their XX combination, must inherit the gene for orange from both parents to have an orange coat. This is why around 80% of ginger cats are male.

The X chromosome also plays a role in the calico and tortoiseshell coat patterns. These patterns are a result of X-inactivation, which occurs during embryonic development. In female cats, only one X chromosome in each cell is active, while the other is deactivated. This results in a mix of orange and black fur, creating the tortoiseshell pattern. If there is also a white spotting gene present, the cat will have a calico coat. Male calico and tortoiseshell cats are rare and usually occur due to chromosomal abnormalities, such as having an extra X chromosome (XXY).

The X chromosome also interacts with other genes to influence coat colour. For example, the non-agouti gene, which creates a solid coat colour, is epistatic to the orange gene. This means that it overrides the orange gene, resulting in a solid black coat. However, in male cats, the orange gene is epistatic to the non-agouti gene, so even if a male cat has the non-agouti gene, it will be overridden by the orange gene, and the cat will have an orange coat.

How white spotting works

The white spotting gene, also called the piebald or bicolor gene, is responsible for white spots on a cat's coat. The gene is linked to the KIT gene, which is associated with white colouration in many animals. The KIT gene has three possible alleles: W, ws, and w. The W allele results in a completely white cat, dominant over the other alleles and any other colour gene. The ws allele is responsible for white spots of varying sizes, codominant with the w allele for a cat without white spots.

Cats with the N/Ws genotype will have white spotting, transmitting this variant to 50% of their offspring, who are expected to be white-spotted. Cats with the Ws/Ws genotype will have white spotting and transmit this variant to all of their offspring, who are expected to have white spotting.

The extent of white spotting is not definitively associated with the number of alleles, but it is generally observed that homozygous cats have more than half of their body covered in white, while heterozygous cats have less than half. In addition, there may be polygenes that influence the quantity and distribution of white spotting.

It is important to note that not all white spots or patterns are solely caused by the KIT gene alleles. Other genes can also have mutations that result in depigmentation phenotypes.

How to identify coat colours and patterns

Cats' coat colours and patterns are determined by their genetics. While there are two base colours of cat coats—black and orange—a range of genes can dilute or modify these base colours, resulting in the variety of cat colours and patterns that we see today.

Solid Colours

Solid-coloured cats are either pure black or have a gene that dilutes black into another shade, such as brown, blue (grey), lilac, fawn, or cinnamon. For example, Russian Blues are solid black cats with a gene that dilutes black to grey.

Tortoiseshell

Tortoiseshell cats have a mix of black and red (or their diluted versions of lilac/lavender and cream). The red colour is carried on the X chromosome, which is why tortoiseshell cats are predominantly female. Male tortoiseshells are rare and usually sterile.

White

Solid white cats can be the result of a dominant white gene that masks the cat's actual colour. Alternatively, they may be albino, lacking the enzyme that produces melanin. True albino cats are extremely rare, so most white cats are not albinos.

Bicolour

Bicolour, or bicolor, refers to a coat of white and one other colour. When a bicolour cat has mostly coloured fur, specific names are used to describe the patches of white, such as "locket" for the chest, "mittens" for the paws, and "buttons" for patches on the abdomen. A black cat with white paws, belly, and sometimes face is often called a "tuxedo".

Tabby

Tabby is a pattern rather than a colour. The main tabby patterns are agouti (ticked/Abyssinian), mackerel, classic, and spotted. Agouti tabbies have ticked fur with almost no striped markings, while mackerel tabbies have thin stripes and classic tabbies have blotched markings. Spotted tabbies can be due to broken mackerel stripes or a spotting gene.

Tricolour/Calico

Tricolour, or calico, refers to a pattern of white, black, and red (or their diluted versions of cream and blue). As the amount of white increases, the patches of red and black become more clearly defined, creating a calico pattern.

Colourpoint

The colourpoint pattern is most commonly associated with Siamese cats but can appear in any non-pedigree domesticated cat. Colourpoint cats have dark colours on their face, ears, feet, and tail, with a lighter version of the same colour on the rest of their body.

Dilution Genes

There are several dilution genes that can lighten a cat's coat colour. For example, the dilute gene lightens orange to cream and black to grey. The dilute modifier gene further lightens diluted colours.

Length and Texture

Cat fur can be short, long, curly, or hairless. Most cats are short-haired, but certain breeds are known for their long hair, such as Persians, Ragdolls, and Maine Coons. Some breeds, like the Sphynx, are hairless.

Frequently asked questions