Observations on chiasmata in mouse diplotene oocytes and spermatocytes.

Complete chromomere maps of Swiss mouse in early diplotene oocytes and spermatocytes have been developed. Individual bivalent identification has been used to assign all chiasmata in complete cells of each sex. All chiasmata appeared to be interchromomeric. More chiasmata were found on all oocyte bivalents than spermatocyte, except bivalent 18 where they were equal. There appeared to be non-random distribution of chiasmata in both sexes and 86 out of 169 chiasmata locations were identical on oocytes and spermatocytes. Differences of location between the present study of early diplotene cells and other reports of studies at the later meiotic stages of diakinesis/metaphase I were found.