Chromosome movement during meiotic prophase in crane‐fly spermatocytes. II. Analysis of polarization of chromosomes and their association with the nuclear envelope

Association of bivalent chromosomes with the astral centers and nuclear envelope was analyzed in crane‐fly spermatocytes during the final hours of diakinesis. In contrast to other systems in which movement of chromosomes during diakinesis correlates with the clustering of bivalents near the astral centers, such clustering is not prevalent in crane‐fly spermatocytes. Polarization indices of bivalents calculated 5 to 10 minutes before the end of diakinesis provided evidence for polarization of only a fraction of all bivalents. Similar results were obtained in a large number of fixed cells in which asters and chromosomes were preferentially stained. Ultrastructural analysis of cells in late diakinesis revealed significant contact between bivalents and the nuclear envelope in all 46 cells that were analyzed. The extent of contact in some cells was greater than in others. Sites of contact included the telomeric ends of bivalents, and in some cases the distribution of contact sites suggested the possible involvement of centromeres in chromosome‐nuclear envelope association. The results are consistent with the hypothesis that a dynamic interaction between chromosomes and nuclear envelope may exist during late prophase, when the movement of chromosomes is known to occur.