How does a tiger have stripes?

Question

A vague question, but let me try to explain. My friend explained to me that in females, some cells use one X chromosome, while all others use the other X chromosome. This can result in some differences of appearance of certain individuals. The Wikipedia page on X-inactivation shows an example. There is a picture there that shows a cat with fur of two colors, each showing in seemingly random groups. My friend had explained that when one cell "deactivates" its X chromosome, all of its descendants have the same deactivated X chromosome, so it makes sense that the similar colors appear in groups on the cat's coat.

But it seems tigers' coats are much more complicated than that. The pattern on a tiger's coat is not completely random. They make very discernible shapes. There are clear borders inside which only black fur grows, and outside of which only orange fur grows. How is this possible?

I'm not suggesting that the patters on tigers' fur is in any way related to X-inactivation, since I know that only applies to female mammals. But X-inactivation seems like a "natural" phenomenon, while the stripes on a tiger (or other animals with complex patters) seem a bit more bizarre. How do the cells on a tiger's body know which color to show and still follow the pattern?

Answer 1

It turns out that this was a question that was answered by Alan Turing in the 1950s.

Turing hypothesized there would be two morphogens, an inhibitor/ activator pair, each of which would produce a one of two phenotypes by activation or suppression of a trait. He hypothesized that this would produce a pattern like stripes or other patterns (e.g. black and orange stripes).

This year just such inhibiting/activating pairs produce patterns like ridges in the top of the mouth of mice.

In a broad way, this seems like X-inactivation, where there is an X-inactivation center (XIC) that is inhibited or activated when the cell is created in mitosis. XIC is still hypothetical and undiscovered, but it can create patterns and is non-random.

So I would say that this tiger stripes and X-inactivation may share Turing's mechanism, but the stripes, found in male and female tigers alike is not linked causally to X-inactivation.