When cells are healthy, we don’t expect them to suddenly change cell types. A skin cell on your hand won’t naturally morph into a brain cell, and vice versa. That’s thanks to epigenetic memory, which enables the expression of various genes to “lock in” throughout a cell’s lifetime. Failure of this memory can lead to diseases, such as cancer.

Traditionally, scientists have thought that epigenetic memory locks genes either “on” or “off” — either fully activated or fully repressed, like a permanent Lite-Brite pattern. But MIT engineers have found that the picture has many more shades.

In a new study appearing today in Cell Genomics, the team reports that a cell’s memory is set not by on/off switching but through a more graded, dimmer-like dial of gene expression.