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A few weeks ago I wrote about the genetics of coat color in domestic cats. Now, to follow up, I am going to dive into the wild world of pattern genetics. If you would like a review of basic genetic principles, click the link to the previous article. There is a quick rundown in the beginning.
In genetics, the “wild type” is the genetic profile of an organism that is most common under natural conditions. The wild type ancestral cat was a mackerel tabby with black stripes, short fur, and no white spots [1]. Today, of course, cats come in a wide variety of patterns, even those who live feral and are subject to natural selection. Both human intervention and spontaneous mutations are to credit for this diversity.
Tabby
Let’s start with tabbies, the original cat pattern. Many other cat species share the tabby pattern with domestic cats, usually in the form of rows of spots–spots and stripes are closely related genetically in cats [2, 3]. In order to have a tabby pattern, a cat must first have at least one dominant allele at the agouti locus. The dominant agouti allele causes each individual hair to have bands of darker and lighter pigmentation. This is required for tabby coats and several other patterns which we will come to later.
The wild type mackerel tabby pattern is characterized by thin, parallel stripes darker than the background color. Mackerel tabby is the dominant allele at the Tabby, or Ta, locus, so only one TaM allele is required for the mackerel tabby pattern. The “blotched” or “classic” tabby has large, marbled stripes. This pattern occurs at the same Ta locus. The blotched allele is recessive to the mackerel.
At least two other alleles are involved in tabby patterning, although it was previously thought that there was only one [4]. The Ticked locus has been definitively identified as influencing the type of tabby pattern a cat’s coat has, but another unknown locus or loci may effect how the patterns present [4].
The Ticked locus is epistatic to the Tabby locus, meaning that the genotype at the Ticked locus has an impact on the phenotype coded for by the Tabby locus. If a TiA allele is present at the Ticked locus, the cat will have ticked/agouti fur all over the body, as the TiA allele masks the effect of the Tabby locus. This is usually called an Abyssinian Tabby because the ticked coat is characteristic of the Abyssinian breed. If there are two Ti+ alleles, the cat will not be an Abyssinian tabby, and whatever genotype is at the Tabby locus will show through. Cats with one TiA and one Ti+ allele tend to have some striping on their faces, legs, and tails despite being Abyssinian tabbies.
Tired of talking about tabbies? I hope not, because we still have to go over the special cases! Spotted tabbies have stripes that are broken into spots of varying size. An unknown modifier gene or genes are believed to alter the expression of mackerel tabby stripes to create spotted tabbies [4]. The charcoal Bengal/Savannah patterns are a variety of tabby caused by an agouti gene inherited from the Asian Leopard Cat. Charcoal tabbies have decreased red tones in their coats, giving them a cooler, grayer appearance. They also have a dark nose and “Zorro” mask on the face and a dark cape down the back. There are a shocking number of other types of modified tabby, but the genetics behind them are hazy. I will leave you with a handy infographic showing you what they look like and move on to the next pattern.
Silver and Gold
Agouti hairs would normally have alternating bands of light and dark pigment corresponding to the cat’s coloring, but there are a couple genes, or possibly gene families, which can change the way pigment is deposited on agouti fur. A dominant mutation of the Silver/Inhibitor gene inhibits production of phaeomelanin, the yellow or red pigment in cat hair. This causes the light portions of agouti bands to be very pale or colorless rather than yellow. This mutation, by itself, causes tabbies to be silvery and solid-colored cats to have a pattern known as smoke, where there is a pale/colorless band at the bottom of their hair shafts. Their white undercoats give them a “smoky” appearance when their fur is ruffled.
On the other hand is the Wide-Banding trait, only present in agouti cats. It is thought to be caused by a group of related genes, but this is still unclear, and no one quite knows how they work. Whatever the root cause, wide-banding causes the agouti bands on the hair shaft to be larger and/or more numerous. There is a high degree of variation in the way this can present, lending credence to the idea that there is more than one gene involved.
When Wide-Banding occurs alone, the cats are sometimes referred to as “golden” due to the higher degree of yellow pigment in their coats. However, the Silver and Wide-Banding traits can occur together to create other patterns. In either case, cats with Wide-Banding that leaves only the very tip of the hair shaft to show their normal pigmentation are said to be tipped. Those with more of the darker pigment on the end of the shaft are called shaded. There are even more names among cat fanciers for the many different combinations of these phenotypes, but we have more to cover.
Color-point
We touched on color-pointing in the Siamese breed profile, and we will probably circle back to it with other breeds. It is a popular pattern which has been deliberately bred into quite a few breeds. Color-pointing is a kind of partial albinism. These cats have a mutation in tyrosinase, an enzyme required for the production of melanin. The mutated enzyme will only activate below 33 degrees Celsius. As such, the mutation causes temperature-sensitive pigmentation, with the most color deposited on the coolest extremities of the body. There are actually two color-point alleles that result in three somewhat different phenotypes. Both alleles are recessive to the wild type allele but are codominant to each other.
The Himalayan phenotype has the strongest color restriction. It is seen in cats with two cs alleles. These cats have blue eyes and a very light-colored torso, typically cream or ivory. The color-pointing is very high-contrast. The intermediate phenotype is known as Mink and is typical of the Tonkinese breed. They have one cs allele and one cb allele. The eyes are aqua and the torso color is more similar to the points.
The Sepia color-points are not all sepia but are named for the brown Burmese cats wherein the pattern was first identified. This phenotype has copper eyes and is quite low-contrast, with the points and the torso being fairly similar in color. Sepia color-points have two cb alleles. All color-point cats can have points of any color, and the points can also be patterned. Sometimes color-point and white spot patterns can be combined to form new patterns, such as white mittens (characteristic of Birmans) or bicolor. For more on white spots, see the coat color article.
There are a LOT of miscellaneous mutations that I could talk about which are not so widespread or well-documented as the ones I have covered here today. If you would like me to go over them in the future, please let me know. I would be glad to do so. You can also tell me if you never want me to do this again. Feedback is always welcome. :3
Works Cited
- Hampton, N. (1998, March 4). Coat color and pattern genetics of the domestic cat (Felis catus) [PowerPoint slides]. The University of Texas at Austin. https://facultystaff.richmond.edu/~lrunyenj/bio554/cat/index.htm.
- Thomas, E.M. (1994). The tribe of tiger: Cats and their culture. Simon and Schuster.
- Zielinksi, S. (2012, September 20). Same gene guides cheetah and tabby cat coat patterns. Smithsonian Magazine. Link here.
- Eizirik, E., et al. (2010). Defining and mapping mammalian coat pattern genes: Multiple genomic regions implicated in domestic cat stripes and spots. Genetics, 184(1), 267-75. DOI: 10.1534/genetics.109.109629
Published April 10th, 2020
Updated June 14th, 2023
