An analysis of the chromomere map and chiasmata characteristics of human diplotene spermatocytes.

A complete chromomere map of early/mid diplotene human spermatocytes has been developed which permits identification of each bivalent. Bivalents 9, 16, 17, and 19 demonstrated unique cytogenetic characteristics at this meiotic stage. The mean chiasma frequency per spermatocyte was 45.33 +/- 4.52 (ranging from 32 to 58) with 28% of bivalents having one chiasma, 38% having two, and 27% having three. The remaining 7% had four or more chiasmata. Fifty-eight percent of chiasmata were located distally, 31% centrally, and 11% proximally. Univalents were rare. The availability of human diplotene spermatocyte maps permits exploration of many basic questions of recombination with accuracy.