Tortoiseshell, calico or tri-colour describes the coat colouring found exclusively in female cats, with patches of orange, black, chocolate, and white. Tortoiseshell cats are also fondly called 'torties'. These cats are renowned for their independent and resilient nature, although some people prefer to call them temperamental. Their individual nature perhaps mimics their individual coat colours as no two torties will be identical in markings. Cats of this colouration are also believed to bring good luck in the folklore of many cultures, such as Scotland and Ireland.
Cats have 19 pairs of chromosomes, half inherited from the mother and the other half inherited from the father. Like humans, one of the 19 pairs of chromosomes (Y) is called the "sex" chromosome, as it determines the gender of the cat. Females are XX and males XY. That is basic genetics, which is similar to humans.
In cats, they also have gene codes for fur colour, and that is what sets the torties apart from the other cats. This genetic coding is somewhat similar to how hair colour is different in humans, except that in human genetics, the coding for hair colour is less complicated. In cat fur colour genetics, the "orange" gene is known as "O" and is carried only on the X chromosome, thus, it is called a "sex linked" colour. There are two alleles, “O” for orange, which is dominant, and “o” for non orange, which is recessive. The recessive allele allows full expression of a non-orange colour, which is usually black. Therefore, this can produce two phenotypes (either black or orange) in male cats, and three phenotypes (black, orange and tortoiseshell) in females.
Torties have two X chromosomes, one carrying the gene for orange coat colour and the other the black coat colour. Therefore, torties can only be females due to the absence of the Y chromosome. For a cat to be a tortie, she must express both the “O” and “o” simultaneously (Oo). The tortie patchwork effect in female cats for the “O” gene (Oo) is due to a process called the "X chromosome inactivation". As the embryo develops, one or the other X chromosome in every cell in the embryo tissue is randomly inactivated, while the other X chromosome is expressed. This only shows up in pigment producing cells.
Cats have 19 pairs of chromosomes, half inherited from the mother and the other half inherited from the father. Like humans, one of the 19 pairs of chromosomes (Y) is called the "sex" chromosome, as it determines the gender of the cat. Females are XX and males XY. That is basic genetics, which is similar to humans.
In cats, they also have gene codes for fur colour, and that is what sets the torties apart from the other cats. This genetic coding is somewhat similar to how hair colour is different in humans, except that in human genetics, the coding for hair colour is less complicated. In cat fur colour genetics, the "orange" gene is known as "O" and is carried only on the X chromosome, thus, it is called a "sex linked" colour. There are two alleles, “O” for orange, which is dominant, and “o” for non orange, which is recessive. The recessive allele allows full expression of a non-orange colour, which is usually black. Therefore, this can produce two phenotypes (either black or orange) in male cats, and three phenotypes (black, orange and tortoiseshell) in females.
Torties have two X chromosomes, one carrying the gene for orange coat colour and the other the black coat colour. Therefore, torties can only be females due to the absence of the Y chromosome. For a cat to be a tortie, she must express both the “O” and “o” simultaneously (Oo). The tortie patchwork effect in female cats for the “O” gene (Oo) is due to a process called the "X chromosome inactivation". As the embryo develops, one or the other X chromosome in every cell in the embryo tissue is randomly inactivated, while the other X chromosome is expressed. This only shows up in pigment producing cells.
(Source of Picture)Picture above depicts the patchy colouring
result of random activation and inactivation of the X chromosomes.
result of random activation and inactivation of the X chromosomes.
Then again, it is not entirely true to say that torties can only exist as females. This is where the interesting part on genetic mutation comes in. It was reported that for a male to be a tortoiseshell, he must first have a genetic mutation that causes the male to have two X and one Y chromosome (XXY). The extra X chromosome usually renders the male tortie infertile. It is estimated that only one in about every 1000 torties is male, and that only one in 10000 is fertile. In cases where male torties are fertile, the cats may be a chimera (a single individual formed from 2 fused embryos; at least one of which was male). Therefore, it is possible for a male to be a tortie, but only due to a genetic mutation.
Another odd tidbit in the tortie genetic coding is that you can almost never clone a tortie. It was reported that when a tortoiseshell cat is cloned, a tortie is never the result. A cat of one or the other of the constituent colours is usually obtained. This means that if you had cloned a black / orange tortoiseshell, the clone will be either orange or black. This is once again due to the “X-linked Inactivation” process in the embryo cells.
-By: Kua Chang Yan Ivan, S41580662, P10-
References:
1. Sarah Hartwell (2008). Tortoiseshell and Tri-colour Cats.Accessed 29th April 2009
2. Ozpets (2007). Articles: Tortoiseshell, Calico and Ginger Cats.Accessed 29th April 2009
3. CatWorld (2009). Why are Tortoiseshell Cats Female & Red Cats Male?Accessed 29th April 2009
For Reading:
Click: HERE, HERE and HERE.
Another odd tidbit in the tortie genetic coding is that you can almost never clone a tortie. It was reported that when a tortoiseshell cat is cloned, a tortie is never the result. A cat of one or the other of the constituent colours is usually obtained. This means that if you had cloned a black / orange tortoiseshell, the clone will be either orange or black. This is once again due to the “X-linked Inactivation” process in the embryo cells.
-By: Kua Chang Yan Ivan, S41580662, P10-
References:
1. Sarah Hartwell (2008). Tortoiseshell and Tri-colour Cats.
2. Ozpets (2007). Articles: Tortoiseshell, Calico and Ginger Cats.
3. CatWorld (2009). Why are Tortoiseshell Cats Female & Red Cats Male?
For Reading:
Click: HERE, HERE and HERE.
