A zebra’s stripes, a seashell’s spirals, a butterfly’s wings: these are all examples of patterns in nature. The formation of patterns is a puzzle for mathematicians and biologists alike.

Weird circles keep popping up around the world, but Alan Turing predicted them in 1952. Here's what they mean—and how the legendary scientist got them so right.

Examples of human chromosome banding patterns (new). In each set of four chromosomes, the first two are homologs from one cell, while the 3rd and the 4th are examples from other cells.