The strange stripes on apples--known as twin spotting--might occur because a cell had two copies of a gene for color. One copy might be a light variant, the other dark. When the cell divided, it accidentally bequeathed two dark variants to one daughter cell, and two light ones to the other. When those cells multiplied, their daughters would inherit those new combinations. And since they grew next to each other, the result would be dark and light stripes. As geneticists studied these peculiar plants more carefully, they gave them a new name: mosaics.