Table 1 Fates of co-opted genes under four different evolutionary scenarios

A

C

Plesiomorphic function lost

Direct co-option with a complete functional shift: gene has derived function

Co-option of a duplicated element, complete functional shift in one of the copies: one copy shows only the derived function, the other retains the plesiomorphic function

B

D

Plesiomorphic function retained

Direct co-option with retention of plesiomorphic function: gene shows both plesiomorphic and derived functions

Co-option of a duplicated element with retention of plesiomorphic function: one copy shows both plesiomorphic + derived functions, the other retains the plesiomorphic function