Gene conversion between unlinked sequences in the germline of mice.

Gene conversion between homologous sequences on non-homologous chromosomes (ectopic gene conversion) is remarkably frequent in fungi. It is thought to be a consequence of genome-wide homology scanning required to form synapses between homologous chromosomes. This activity provides a mechanism for concerted evolution of dispersed genes. Technical obstacles associated with mammalian systems have hitherto precluded investigations into ectopic gene conversion in the mammals. Here, we describe a binary transgenic mouse system to detect ectopic gene conversion in mice. Conversion events are visualized by histochemical staining of spermatids, and corroborated by polymerase chain reaction amplification of transgenes in spermatozoa. The results show that conversion between unliked, hemizygous lacZ transgenes is frequent in the male germline, ranging from 0.1 to 0.7% of spermatids. Genomic location may affect the susceptibility to recombination, since the frequency varied between lines. The results suggest that homologous genes can undergo concerted evolution despite being genomically dispersed. However, mechanisms may exist to modulate this activity, enabling the divergence of duplicated genes.