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Tortoiseshell and calico cats (or tricolor) explained

Throughout history, tortoiseshell and calico cats, also known as tricolor cats, have been very special animals. In some countries, they are considered to be symbols of good luck, probably because they are not very common. Let´s find out why they are called “tricolor”, how genetics influences their colors and why they are associated with females.

Why are tortoiseshell and calico cats considered to be tricolored?

Tricolor cats can be present in all breeds of cats as they do not belong to one in particular; but for a cat to be considered tricolor, she must have the following combination of three colors:

1) Orange or red.

2) Black.

3) White.

How does genetics influence tricolor combinations?

Genetics is a very extensive topic, so I will try to summarize some basic concepts that will help understand how it influences the colors of cat coats.

When the egg and the sperm join during fertilization, the mother contributes with nineteen chromosomes containing genetic information and the father, contributes with  the other nineteen, amounting to a thirty-eight chromosome genotype. One of the nineteen chromosomes from the mother is the sex chromosome (X), and one of the nineteen chromosomes from the father, is either the sex chromosome (X) or (Y). 

Chromosomes are structures inside the nucleus of each one of our cells. Inside those chromosomes there are genes (formed with DNA sections) which determine the genetic heredity. Sex chromosomes (X) – (Y) define if the new kitten will be a male or a female, but the one provided by the father will be the most relevant, for he´s the one that has the Y chromosome. Only 2 combinations are possible:

If the sex chromosome X passed  by  the mother joins the X chromosome passed by  the father: female

If the sex chromosome X provided by the mother joins the Y chromosome provided by the father: male

Why is this relevant to tricolor cats?

The reason why all this is related with tortoiseshell cats is that the gene that codes for orange color is linked to chromosome X. As females (XX) have two X chromosomes, they can portray two colors at the same time (black and orange). As males (XY) only have one X chromosome, they can portray either black or orange, but not both.

Genes can be dominant (they manifest themselves) or recessive (they remain inactive while the dominant gene is present). Dominant genes are represented with capital letters and recessive ones, with small case letters. We can summarize it this way:

XOXO=orange: orange female cat (combination of two dominant genes coded for orange color).

Female, orange-colored catImage / James Yardley.

XoXo= not orange: black female cat (combination of two recessive genes coded for orange color).

XOXo = orange and not orange: tricolor female (combination of a dominant gene and a recessive one). 

Tricolor, carey catImage: “Ksmith4f”. 

XOY= orange: orange male cat (orange dominant gene). Remember that chromosome Y is not linked to any color.

XoY= not orange i.e. black: Black male (recessive orange gene).

White color in cats is due to the W (White) gene, which produces the complete depigmentation in their coat. The result is a completely white cat.

But in the case of tricolor females, white patches are caused by a different gene, the S gene (partially white), whose expression will range from a large extension of white to a very little one.

In the case of calico female cats, this gene will express itself in the form of distinctive white spots and, in the case of tortoiseshell female cats; it will do so in an intermingled way.



Types of tricolor female cats

As stated in the beginning of the article, there are 2 types:

– Calico: they are mainly white (abdomen, chest, legs and chin) with distinct black and orange patches.

Tricolor, calico cat

Image /Caspian Blue.

In the case of Calico females with diluted colors, there are the same colors but in paler tones: cream and bluish-gray instead of orange and black.

Calico cat in diluted colorsImage / “Squeaky Knees”.

– Tortoiseshell: they are called that way because their coat pattern resembles the shell of a turtle. The three colors are mixed asymmetrically and they don´t have patches. White color is practically absent. There are short-haired and long-haired female cats with this pattern. 

Carey cat with long hair

Diluted colors are very common as well: cream and bluish-gray. They manifest when gene d, the one responsible for pigment density decrease, is present.

Diluted colors in the presence of the recessive gene (dd):

Original color    Diluted

Black                       Grayish-blue

Orange                    Cream 

Chocolate               Lilac

Cinnamon              Fawn

Diluted carey catImage: “Barryap”.

– Striped tricolor cats: a subdivision of both calico and tortoiseshell cats; some of them have  striped patterns.

Tricolor, striped catImage / Lewis Collard.

Are there tricolor male cats?

For a tricolor pattern to be present, there must be a combination of a dominant and a recessive orange gene. This combination is only possible in (XX) that is, in female cats. However, there are a few exceptions and tricolor male cats can be found. The most common one is due to a genetic abnormality, and it takes place when the cat has three sex chromosomes (XXY) instead of two (XY). This is known as the Klinefelter syndrome, and tricolor male cats are infertile.