MtDNA Genomics of Gadinae:
Phylogenetic & Biogeographic implications
(MW Coulson, HD Marshall, P Pepin, and SM Carr 2006. Genome 49,1115-1130)

    Analysis of complete mtDNA genomes (ca. 17Kbp) of Atlantic cod (Gadus morhua) and relatives porovides a fully-resolved evolutionary tree that clarifies their phylogenetic and biogeographic relationships. Atlantic Cod on either side of the Atlantic Ocean are more closely genetically related (52 differences) than are Pacific Cod (G. macrocephalus) from either side of the Pacific Ocean (73 differences). Greenland Cod (G. macrocephalus ogac), previously regarded as a separate species, are a recently derived genetic subpopulation of Pacific Cod, and represent a secondary re-invasion of the Atlantic. Alaska or Walleye Pollock (Theragra chalcogramma) are more closely related to Atlantic Cod. They therefore represent an independent invasion of the Pacific basin, and should be referred to the genus Gadus as originally described (Gadus chalcogrammus).