Scientists have now sequenced the genome of the Atlantic cod
, revealing something unusual: the cod is missing an important component of the adaptive immune system
found in almost all jawed vertebrates. In particular, when the researchers compared the cod's genome to that of the stickleback (a closely related fish that has already been sequenced), they saw that the Atlantic cod does not have genes that code for the proteins MHC II
, CD4
, and invariant chain, all of which work together to help the body recognize and fight off invading bacteria and parasites. But the missing genes is not a death sentence for the cod. To make up for the lack of MHC II, the cod has ten times more genes for MHC I
—another component of the immune system—than other vertebrates. The researchers think that MHC I system may be picking up some of the functions of ...
