ALT This diagram shows how environmental stressors like antifungal drugs or high temperatures can trigger a molecular chain reaction inside fission yeast cells, which share many of the same pathways as human cells.\n\nExternal signals funnel through two internal communication networks into a molecular dimmer switch called the heterochromatin heritability regulatory hub, or HRH. When stress turns the dimmer up, the HRH can drive the assembly of tightly packed DNA regions called heterochromatin, locking certain genes off. Those silencing patterns can then be passed on to daughter cells when the cell divides \u2014 no changes to the underlying DNA sequence required. Image Credit: Shiv Grewal