Schematic drawing for the diversification of the helical cytokines and their receptors during the evolution of the osteichthians. Open boxes are for coding exons, black parts for 3' and 5' non coding regions. Broken lines are for introns; their phase is indicated. For the receptors, broken boxes indicate that all D200 part of larger proteins. Exons are numbered A1 (for the first exon coding the SD100A) to B2 (second exon coding the SD100B). Conserved cysteines are indicated as vertical bars over the exon boxes. The retroposition event leading to typeI IFNs has only been observed in amniotes and is therefore labeled "amniote specific". Data from other sarcopterygians could lead to a revision.