GENETIC BASIS OF ANTIBODY DIVERSITY SEE APPENDIX (9) SOUTHERN BLOTTING Underlying the development of antibody diversity is a unique pattern of gene organization and molecular events. THREE FAMILIES OF IMMUNOGLOBULIN

Underlying the development of antibody diversity is a unique pattern of gene organization and molecular events. THREE FAMILIES OF IMMUNOGLOBULIN GENES exist in mammals, one encoding HEAVY chains, another KAPPA chains, and the third LAMBDA chains. Each of these clusters contains one or more constant region genes and a number of variable region gene segments. The formation of a complete variable region of a light or heavy chain requires the joining of two or three separate genetic elements by a process of GENE REARRANGEMENT; a separate DNA rearrangement in the heavy-chain complex is required for subsequent CLASSSWITCHING. Both germ-line and somatic events contribute to antibody diversity, including COMBINATORIAL JOINING, SOMATIC MUTATION and COMBINATORIAL ASSOCIATION. This gene organization and the requirement for gene rearrangement is unique to immunoglobulins, with the single exception of the related family of genes encoding the T-CELL RECEPTORS, whose functions will be discussed later.