Meiotic Recombination: Crossing-over into Livestock Species

The production of viable gametes is an integral part of reproduction and the sustainability of the livestock industry. Homologous recombination or cross-overs (CO) is an extremely important process in gametogenesis that contributes to genetic variation and ensures proper chromosome segregation. In virtually all organisms studied thus far, it is clear that at least one CO per chromosome arm is necessary to avoid mis-segregation. Furthermore, the location of CO is not random, exhibiting some preferences (called hotspots) and with the presence of one CO “interfering” with the proximity of a second. Importantly, failure or improper placements of recombination represent a significant contribution to developmental defects, embryonic and fetal loss and infertility. Despite the importance of these issues we know very little about meiotic recombination rates in livestock species. We have characterized and quantified the number of recombination events from Targhee and Suffolk rams. Testicular tissue samples were taken and spermatocytes were spread and fixed on slides. Immunofluorescent staining of pachytene stage prophase cells were used to identify the synaptonemal complexes (SYCP3) and CO events (MLH1). The numbers of CO and their chromosomal locations were analyzed. Our data suggests that recombination rates are higher in sheep (~61.5) than in estimated in cattle (~47.5), despite similar genome size and number of chromosome arms. This research provides important information regarding recombination rates in sheep spermatocyte. Furthermore, this research contributes valuable information towards a greater understanding of the factors that control meiotic recombination to enhance reproduction and genetic predictions.