Evolution of pseudogenes in the immunoglobulin V H-gene family of the mouse

A quantitative analysis of the complexity of the J558 V_H-gene family in the mouse immunoglobulin heavy chain (Igh) gene locus has been performed. Considerable variations in the degree of complexity are observed in various Igh haplotypes derived from laboratory mice and wild mice. The BALB/c strain shows the highest degree of complexity of the J558 V_H-gene family when all mice are compared. Multiple gene duplications seem to have occurred in the BALB/c-derived J558 V_H-gene family less than 1–2 million years ago. This dating is supported by the divergence in coding and flanking regions of three strongly homologous V_H-region genes. Two of these genes were generated by the duplication of a pseudogene about 1.5 × 10⁵ years ago. A recent expansion of the J558 V_H-gene family and therefore little time for evolutionary drift may explain why most of the pseudogenes in this family exhibit a largely intact structure. We also describe two V_H-region genes which represent older pseudogenes in states of progressive disintegration.