Unusual heavy chains of human IgG immunoglobulins: rearrangements of the ch domain exons.

Unusual combinations--unexpected sets, excess of lack--of antigenic determinants, or Gm allotypes, on the constant regions of the heavy chains of the human IgG1 and IgG3 immunoglobulins are accounted for in terms of genetic events (exchanges, duplications and deletions) involving the DNA sequences, or exons, coding for the three CH1-, CH2- and CH3 domains of the gamma 1 and gamma 3 chains. Equal and unequal cross-overs at the level of the introns without damage to the CH exons are postulated.