Figure 2.
Proposed evolution of a proto-centriole capable of nucleating a primitive cilium-like structure. (A) Evolution of tektins allows formation of stable microtubule doublet and triplet structures. (B) Acquisition of one or more appendage proteins allows docking of proto-centriole onto cell cortex. (C) Microtubules can extend from the end of the double structure. (D) If microtubules extend from the end of a docked doublet it would produce a primitive cilium-like structure that could be used for sensory or gliding functions.