Serum complement 'supergenes' of the major histocompatibility complex in man (complotypes). 
The loci for the complement proteins C2 and BF, and the two loci for C4 are closely linked to one another.  In many hundreds of meioses no crossing over has been detected between these loci.  In addition, the alleles of these four loci occur in specific combinations not predicted by their gene frequencies in much the same way as alleles of the Rh and MNS systems.  These units are termed complotypes.  There are 14 complotypes with frequencies in excess of 1% in our study population of normal sixth chromosomes from Caucasians.  Since they are also intimately associated with HLA-DR, comploytypes may also be of importance in screening programs for transplantation.