Differential staining and chromatin packing of the mitotic chromosomes of the newt Triturus cristatus

Mitotic metaphase chromosomes of cold-treated Triturus cristatus show a characteristic pattern of constrictions, most of which lie close, though not immediately adjacent, to the centromeres. The chromatin in these cold-induced constrictions stains intensely with Giemsa. Cold-treated spermatogonia show spiral structure throughout the metaphase chromatids; the packing of chromatin fibrils is much tighter in the constricted regions than elsewhere, and the gyres in the constricted regions are narrower and of shorter pitch.