Evolution of reproductive modes and vitellogenins in bony vertebrates. White circles indicate the ancestral gene duplications (1 and 2) that led to the establishment of the vitellogenin cluster (VGC). Yellow stars indicate innovations in the reproductive mode; crosses indicate Vtg gene losses. FSGD, fish-specific genome duplication; MYA, million years ago. The timing of establishment of the vitellogenin cluster in relation to the emergence of vertebrates and the occurrence of the 1R/2R genome duplications remain elusive and will require additional data from cartilaginous fishes, agnathans and non-vertebrate chordates. Adapted from  and revised and expanded using fish data from [7,8].
Braasch and Salzburger Journal of Biology 2009 8:25 doi:10.1186/jbiol121