A genetic polymorphism of the complement component factor B in chickens not linked to the major histocompatibility complex (MHC).

The complement component factor B in chickens exhibits a genetic polymorphism with three common phenotypes, F, F/S, and S. These phenotypes segregate in flocks of chickens homozygous for the MHC (B complex) of the chicken. Furthermore, a genetic analysis has shown that the described factor B polymorphism is not linked to the B complex. It is not known whether the molecular basis for this polymorphism is due to the existence of allelic forms of the structural gene or to some posttranslational modifications, but the finding is discussed in view of the close linkage of factor B polymorphism with the MHC of all mammalian species investigated so far.