Fig. 1.

Shown is a phylogenetic tree for the phytoene synthase from various organisms including cyanobacteria, algae, and higher plants. The arrow indicates an ancient gene duplication event creating a class I PSY (I) and a class II PSY (II). Stars indicate where later gene duplications led to creation of paralogous genes found within one species. Major groups of organisms are labeled to allow comparison between the phylogeny of PSY and algae evolution. Note that the overall phylogeny of PSY follows the currently accepted system of classification of algae