Chromosome no. 1 of Crepis capillaris shows defined 3D-shapes in mitotic prophase

The shape of mitotic prophase chromosomes has been studied in root tip nucl ei by confocal microscopy and 3D-image analysis. Crepis capillaris chromoso me no. 1 was used as a test object. Chromosome conformation was studied in early, mid- and in late prophase. In mid- and late prophase, individual chr omosomes could be distinguished on the basis of their length. Early prophas e chromosomes could not be distinguished as individuals. The central axes o f prophase chromosomes were traced with an automated computer procedure and then represented as a string of 3D coordinates. This representation facili tated measurement along the chromosome axis of shape parameters such as cur vature (amount of bending), torsion (helical winding) and torsion sign (hel ical handedness). Stretches of early prophase chromosomes showed full helic al turns, which could be left- or right-handed. In the later prophase stage s curvature and torsion were statistically analysed. Our data on 40 mid-pro phase chromosomes no. 1 show that they are still highly curved, but full he lical turns were no longer found. Instead, an overall meandering pattern wa s observed. In late prophase, one central loop persisted, flanked by two pr eferential regions of high curvature.