(A) In a trans memory system, the two copies of FLC are coordinately regulated and only two mitotically heritable states are possible (FLC-Venus/FLC-mCherry ON/ON, OFF/OFF). (B) In a cis memory system, the two copies of FLC can be maintained in alternative expression states, so four mitotically heritable states are possible (FLC-Venus/FLC-mCherry ON/ON, ON/OFF, OFF/ON, OFF/OFF). (C) Non-vernalized roots of FLC-mCherry × FLC-Venus F1 plants show uniform expression of FLC-Venus and FLC-mCherry in all nuclei. (D) After vernalization such plants can epigenetically repress a single-gene copy, while the other remains activated. The following notation is used to indicate files of cells in the various expression states: Both expressed, vc; FLC-Venus only, v; FLC-mCherry only, C. Scale bars, 50 μm.