Two-to-two correspondences between the Japanese eel and medaka chromosomes. (A) Teleost-specific whole genome duplication (TGD) and subsequent major chromosomal rearrangement events. Kasahara et al.  described the estimates of the teleost ancestral chromosomes, labeled from A to M, and the eight chromosomal rearrangements. Phylogenetic relationships among fishes and their divergence times are from Broughton et al. . The eel lineage diverged from other teleost lineage soon after the TGD. (B) Re-arrayed the Oxford grid between the Japanese eel and medaka. According to the ancestral genomic structures of zebrafish-medaka, the medaka chromosomes are re-arrayed. (C) Two-to-two relationships among the ohnologous chromosomes. Eel linkage group 3 (Aja3) and Aja16 shared the conserved segments with medaka chromosome 12 (Ola12) and its paralogous chromosome of Ola9. Aja3 and Aja16 also have two-to-one relationship with the gar chromosome 21 (Loc21). Similar relationships are observed in Loc11-Aja4/Aja7-Ola11/Ola16, Loc3-Aja13/Aja2-Ola3/Ola6 and Loc5-Aja12/Aja6-Ola5/Ola7.