The Epigenetics Revolution by Nessa Carey

Author:Nessa Carey
Language: eng
Format: epub, mobi
Tags: Science/Life Sciences/Genetics and Genomics
Publisher: Columbia University Press
Published: 2011-09-09T16:00:00+00:00

Learning from the epigenetic cat

Not just any old cats, but specifically tortoiseshell ones. You probably know how to recognise a classic tortoiseshell cat. It’s the one that’s a mixture of black and ginger splodges, sometimes on a white background. The colour of each hair in a cat’s coat is caused by cells called melanocytes that produce pigment. Melanocytes are found in the skin, and develop from special stem cells. When melanocyte stem cells divide, the daughter cells stay close to each other, forming a little patch of clonal cells from the same parent stem cell.

Now, here’s an amazing thing: if a cat’s colour is tortoiseshell, it’s a female.

There is a gene for coat colour that encodes either black pigment or orange pigment. This gene is carried on the X chromosome. A cat may receive the black version of the gene on the X chromosome inherited from her mother and the orange version on the X chromosome inherited from her father (or vice versa). Figure 9.5 shows what happens next.

So the tortoiseshell cat ends up with patches of orange and patches of black, depending on the X chromosome that was randomly inactivated in the melanocyte stem cell. The pattern won’t change as the cat gets older, it stays the same throughout its life. That tells us that the X inactivation stays the same in the cells that create this coat pattern.

We know that tortoiseshell cats are always female because the gene for the coat colour is only on the X chromosome, not the Y. A male cat only has one X chromosome, so it could have black fur or ginger fur, but never both.

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