Model of a chromosome segment in interphase

A three-dimensional model of a chromosome
segment shows that the constitutive heterochromatin
(C-band) in the centromere region is
very tightly wound. In the light G-bands, the
euchromatin is relatively loosely packed, and in
the dark G-bands, somewhat more tightly
packed. (With kind permission of the author,
from Manuelidis, 1990, copyright 1990 by the
AAAS).