Turing worked on a family of partial differential equations called "reaction-diffusion equations", and determined that for particular choices of the parameters, they produce phenomena similar to tiger stripes, leopard spots, and the like. One doesn't have to describe this in terms of biology; mathematically it is already interesting on its own.

But how much cooler is it that this can be observed by a visit to a zoo! He (or perhaps biologists who studied his work?) conjectured that some biological process behaved according to his equations, and therefore produced the behavior they model. However, until now, no one had ever found such a process.