The effect of colcemid and aluminum on the ultrastructure of human metaphase chromosomes.

Recently, we have reported new basic information on the ultrastructure of human metaphase chromosomes using both scanning and transmission electron microscopy. This includes the observation of a bipartite chromatid structure (BCS) for some metaphase chromatids, a "zipper-like" configuration (ZC) between chromatids that likely resulted from chromatin coiling, and a "brush-like" border (BB) that was observed primarily on chromosomes that were not exposed to colcemid. Now we have examined the effects of colcemid and several metals on the occurrence of the BCS, the ZC, and the BB. Although we do not as yet know the function of the zipper-like and bipartite chromatid configurations, we have found that colcemid clearly caused a significant increase in the occurrence of chromosomes with a BCS or ZC. We also have confirmed our original observation of increased occurrence of the BB on chromosomes not exposed to colcemid and finally, have shown that aluminum and other metals had some effect on the frequencies of the BCS, the ZC, and the BB with and without exposure to colcemid.