The Voigt Lab programs randomness into living cells, harnessing chance binding of recombinase enzymes to DNA to create genetic circuits that partition bacterial populations into distinct cell types at precise, predictable ratios (shown here as a time-lapse colony). Individual cells permanently switch into green or magenta fluorescent-labelled states. The probability of a given outcome can be tuned from 5% to 96%, enabling engineered microbes to self-diversify into cooperative populations with applications from agriculture to medicine.