Page 528 - Veterinary Immunology, 10th Edition

VetBooks.ir Gene Conversion

Mammals other than the human and mouse may have only a few V
genes, and gene recombination cannot explain their

immunoglobulin diversity. In these species, V-region diversity is
generated by gene conversion (Fig. 17.11). Species that employ gene
conversion must have available a supply of multiple V genes or
pseudogenes. (Pseudogenes are segments of DNA that are defective
and so cannot be transcribed.) During gene conversion, B cell

cytidine deaminase inserts a uracil, which is then removed, leaving
a gap in the nearest V gene. This gap is then filled by randomly
selected short segments of DNA obtained from an upstream V-

region gene or pseudogene. The “repaired” V gene will therefore
have a different sequence than its precursor. Some of these gene
conversion events may not generate a functional V region. In these
cases, these defective B cells are eliminated.

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