Question

Explain how polymorphism and co-dominance in the immune system provides an advantage to an individual.

Answer 1

The genes encoding the major histocompatibility (MHC) molecules are among the most polymorphic genes known in vertebrates. Since MHC molecules play an important role in the induction of immune responses, this polymorphism is probably due to selection for increased protection of hosts against pathogens. Thus MHC is highly polymorphic; that is, there are multiple variants of each gene within the population as a whole. The MHC genes are, in fact, the most polymorphic genes known.  Polymorphism is probably due to selection for increased protection of hosts against pathogens.

Expression of MHC alleles is codominant, with the protein products of both the alleles at a locus being expressed in the cell, and both gene products being able to present antigens to T cells.