7. Hopi Hoekstra and her colleagues have revealed how mutated versions of two genes arose and spread in the beach populations, causing animals in these areas to develop with white fur. … At some point in the past, mutations altered the sequences of these two genes, and these changes caused beach mice to develop with lighter fur. … Both of these mutations lightened the color of mouse fur, and together they yielded very white mice.

Emlen, Douglas J, Animal Weapons_ The Evoluti…, loc. 618