An inventory of functional V, D, and J gene segments in the germ-line DNA of one human reveals 51 VH, 25 D, 6 JH, 40 VK, 5 JK, 31 VX, and 4 JX gene segments. In addition to these functional segments, there are many pseudogenes. It should be borne in mind that these numbers were largely derived from a landmark study that sequenced the DNA of the immunoglobulin loci of a single individual. The immuno-globulin loci of other individuals might contain slightly different numbers of particular types of gene segments.
In the mouse, although the numbers are known with less precision than in the human, there appear to be about 85 VK gene segments and 134 VH gene segments, 4 functional JH, 4
functional JK, 3 functional JX, and an estimated 13 DH gene segments, but only three VX gene segments. Although the number of germ-line genes found in either humans or mice is far fewer than predicted by early proponents of the germline model, multiple germ-line V, D, and J gene segments clearly do contribute to the diversity of the antigen-binding sites in antibodies.
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