concept

Cis-regulatory element

Stretches of non-coding DNA around a gene that act as switches, deciding when, where, and how strongly that gene turns on. This is where evolution does most of its real work: rather than risk redesigning a precious master gene (which tends to break everything at once), evolution simply retunes a switch - adding a spot of colour, suppressing a limb on one body segment, dialling an organ's size up or down - leaving the tool itself untouched.