Figure 1.

(a) An example gene tree showing the seed plant (ζ, red) and angiosperm (ɛ, blue) duplications. The duplication events are constrained using minima and maxima (coloured brackets) based on fossils used to constrain speciation events (black brackets). (b) Gene trees may retain both copies of the duplicate gene (top), or a single copy may be lost (bottom). When concatenating duplicates from different gene families, given that both copies are descended from the same event, their assignment to either side of the duplication is arbitrary. (Online version in colour.)