Although many cell fates are determined by extracellular signals, some fates occur stochastically, potentially to help generate cell-type diversity. Notch (N) signalling, previously implicated in stochastic fate choices, is now shown by Miller et al. to act, somewhat uniquely, by exposing a hidden stochastic fate choice in a photoreceptor cell, which it then tips towards a particular fate (see ). The ommatidia of the Drosophila eye each contain eight photoreceptor cells, R1-R8. During development, R1/R6/R7 precursors become R1/R6's unless N is activated in them to specify them as R7. N is believed to promote R7 fate by repressing the orphan nuclear hormone receptor Svp. But Miller et al. report that svp mutant R1/R6 precursors adopt -stochastically and with equal likelihood - either an R7 or R8 fate, and express both an R7 and R8 marker (later expressing only one). The authors conclude that mutual negative feedback between the R7/R8 programs results in the stochastic adoption of either fate, but that, in parallel, N represses the R8 marker sens to promote the R7 fate.
