Timing and effects of template number for gene conversion of Major Histocompatibility Complex genes in the mouse

Pachytene spermatocytes and haploid spermatocytes from adult mice, as well as testis cells from prepubescent mice were analysed for the presence of gene conversion products resulting from the transfer between the MHC class II genes Ebd and Abk in a PCR assay. Gene conversion products were detected in testis cells as early as in 8 days old mice, where the only existing spermatogenic cells are spermatogonia. The frequency of gene conversion products remains the same as the cells reach meiosis in 18 days old mice or in pachytene cells, and is unchanged after meiosis is completed in haploid spermatocytes, thus indicating that gene conversion is largely completed already in the mitotically dividing spermatogonia. We have furthermore analysed the frequency of gene conversion between the Eb and Ab loci within the same MHC haplotype, the k haplotype. The frequency of such events is the same in animals with one and two copies of the same haplotype, and consequently seems to be independent of template number.