Figure 1

Gene trees and gene duplications. Gene family tree for opsins from four vertebrate species – mouse, chicken, zebrafish and clawed frog. (a) including all 4 taxa. Some nodes represent speciation events, others (marked with a black rectangle) gene duplication events. (b) Including only zebrafish sequences. All the nodes in this tree represent gene duplications, so this sort of tree can be used to study the gene duplication process alone