Fig. 5

Reconstructed evolutionary history of karyotypes from Chordata to Amniota. On the right, a simplified species tree of the Chordata is shown, with WGD events depicted by red stars. The eight lineages represented from left to right are mammals, birds, teleost fish, holostocean fish (gar), cartilaginous fish, cyclostomes (lamprey, hagfish), tunicates (ciona), and cephalochordates (amphioxus). On the left, successive reconstructed karyotypes are shown, with one color for each of the 17 pre-1R chromosomes. The length of each pre-1R chromosome is proportional to its number of genes. For the 17 Chordate Linkage Groups (CLGs) of [7], the size of the colored segment is proportional to the number of genes that are found in the intersection of the CLG with a pre-1R chromosome, although segments corresponding to < 10% of the number of genes of the CLG were omitted for clarity (Additional file 1: Table S7). The karyotype between 1R and 2R was deduced from the pre-1R karyotype and the seven chromosome fusions are shown with purple curvy lines joining the fused chromosomes. The Euteleostomi karyotype was deduced from the Vertebrata karyotype after four chromosome fusions (Additional file 1). The lengths of the Euteleostomi chromosomes are proportional to the number of genes in the homologous Amniota CARs. Finally, the Amniota karyotype differs from that of Euteleostomi by only one chromosome fusion. The Amniota chromosomes were numbered from 1 to 49 (Additional file 1: Table S11 for correspondence with the CARs and number of genes). Black stars under 12 Euteleostomi chromosomes denote predicted ancestral micro-chromosomes