Though there are many more (~1 million) potential antigens than genes in the human genome, it is possible to produce antibodies for virtually all of these owing to transposable genetic elements along a few chromosomal DNA segments.  While the composition of the carboxyl ends of the heavy (~400) and light (~220) amino acid chains in the constant regions (CH, CLare practically identical for all antibody classes, the amino ends of the variable regions (VH, VL) are different for each type.

A single locus exists on human chromosome 14 for immunoglobulin heavy chains, while separate loci exist for the variable regions on chromosomes 2 and 22.  There are only about ten CH and CL genes (constant regions do not interact with epitopes), but 200-300 VL and VH genes.