Pointless to clone a pretty cat
If you have an unusually pretty cat and dream about cloning it one day, you might as well stop dreaming. Two cats with the exact same gene pool can actually look totally different.
Many think that Calico cats, also known as tricolour cats, are the best looking because the female cats have fur with three different colours: Red/orange, black or white. It could be quite tempting to try to clone the prettiest cats in order to conserve their colour patterns and beauty. However, scientist Ragnhild Eskeland at Department for Biosciences would ask cat cloning supporters to dampen their enthusiasm.
The fur colour on cats is decided by which fur colour genes are switched on or off in each individual skin cell, Ragnhild Eskeland explains.
– The fur differs from individual to individual even though the genes er exactly the same. Not even single-egged Calico cat twins look the same, and the fact is that a cloned cat will never look exactly as the original, says Eskeland.
The explanation comes from epigenetics, a science that gathered momentum after the human genome was mapped out in great detail about fifteen years ago.
At the start of the human genome-project in 1990, many dreamt that the total charting of the DNA sequences would reveal all secrets concerning nature versus nurture and trigger a golden age of DNA based medicines. However, the future revealed that genetics and heredity is a complicated matter, more so than the DNA-optimists foresaw.
A random distribution of colour
Heredity is not solely dependent on gene pool, but also depends on which genes are turned on or off. This field of research is called epigenetics, and the Calico cat’s fur colour is an illustrating example on how epigenetics works.
– Cats are like humans in the way that they have sex chromosomes which we can call X and Y. The female cats have two x chromosomes, one from their male parent and one from their female parent. The male cats however, have a Y chromosome from their male parent and an X chromosome from their female parent, explains Eskeland.
Most cats have two colours in their fur, but the Calico cats are special in the way that they have genes for three colours: Red/orange, black and white. The Calico cats have X chromosomes that contains either the gene for red/orange fur or black fur, but noteworthy, the gene for white fur is placed in an "ordinary" chromosome that does not decide the cats sex. And now the weird stuff happens:
The cells in our body are only supposed to have one active X chromosome and consequently one of the X chromosomes must be "turned off", leaving one inactive X chromosome. This makes the fur black on the skin cells where the X chromosome containing the gene for red/orange is turned off, and vice versa.
– The weird thing is that it is a totally random process that decides which X chromosome is turned on or off in each individual cell. Consequently, it is at totally random which fur colour each skin cell will reveal. The pattern of colour in the fur of Calico cats is a random distribution of red/orange and black, Eskeland explains.
The white fur colour follows a different kind of logic. The Calico cats have in fact two genes that can give white fur colour: One gene code produce white dots, while the other gene code creates white patches. The white colour is in fact unpigmented and both white genes dominate red/orange and black ones.
Consequently, the fur is white when the white gene cells are "turned on" because the white genes prohibit pigmentation.
Similar circumstances decide the skin and fur colour of lots of animals, for example giraffes and cattle. However, we probably find the most extreme exemplification of epigenetics in butterflies, where the larva, pupa and the fully grown butterfly contain exactly the same genes.
The different stages of the butterfly are simply decided by which genes are turned on and off.
Translated from Norwegian by Espen Haakstad
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