Evolution of developmental traits.

The evolution of plant development can be studied in many different ways, each of which provides new insights into how plants have been modified over evolutionary time. DNA sequencing shows that most developmental genes are under purifying selection and that obvious adaptive change in proteins is rare. This may indicate that most change occurs in cis-regulatory sequences, that tests for detecting selection lack power, or both. Gene duplications are common and often correlate with divergence of function, as predicted by theory. Studies of gene expression illuminate similarities among structures in disparate plant groups and indicate that the same genes have been deployed repeatedly for similar developmental ends. Comparative functional studies remain uncommon, but promise to illuminate how changing proteins lead to changes in development. Precise characterization of phenotypes by studies of developmental morphology is beginning to occur in some taxonomic groups. The genetic variation necessary for morphological change must originate as allelic polymorphism within populations; such polymorphism has been identified in grasses and in sunflowers, although it is often cryptic.