Immunoglobulin sequence diversity. A plot of sequence variability as a function of position along the sequence of the amino-terminal immunoglobulin domain of the H chain of human IgG molecules. Three regions (in red) show remarkably high levels of variability. These hypervariable regions correspond to three loops in the immunoglobulin domain structure.

[Data from R. A. Goldsby, T. J. Kindt, and B. A. Osborne, Kuby Immunology, 4th ed. (W. H. Freeman and Company, 2000), p. 91.]