Assignment of Chinook salmon (Oncorhynchus tshawytscha) linkage groups to specific chromosomes reveals a karyotype with multiple rearrangements of the chromosome arms of rainbow trout (Oncorhynchus mykiss).

The Chinook salmon genetic linkage groups have been assigned to specific chromosomes using fluorescence in situ hybridization with bacterial artificial chromosome probes containing genetic markers mapped to each linkage group in Chinook salmon and rainbow trout. Comparison of the Chinook salmon chromosome map with that of rainbow trout provides strong evidence for conservation of large syntenic blocks in these species, corresponding to entire chromosome arms in the rainbow trout as expected. In almost every case, the markers were found at approximately the same location on the chromosome arm in each species, suggesting conservation of marker order on the chromosome arms of the two species in most cases. Although theoretically a few centric fissions could convert the karyotype of rainbow trout (2N = 58-64) into that of Chinook salmon (2N = 68) or vice versa, our data suggest that chromosome arms underwent multiple centric fissions and subsequent new centric fusions to form the current karyotypes. The morphology of only approximately one-third of the chromosome pairs have been conserved between the two species.