themselves in the replication of the chromosome in a non-random fashion, thus
being handed down from one cell generation into another (just like DNA), which
is in accordance with the idea of Tsanev and Sendov (1971) that the specific
arrangements of histones along the DNA-chain are kept up during the replication
by specific interactions between the previously existing DNA-bound histones
and the newly-synthesized free histones. Some authors would not agree with
this assertion (Jackson et al., 1975, 1976; Seale, 1976). According to them
histones are randomly distributed upon the self-replicating chromosomes. This is
a serious scientific disagreement. The importance of this problem requires a
definitive solution, which is related to further investigations. More plausible,
however, seems from a general biology standpoint the thesis supporting the
non-random i.e. conservative distribution of histones on both DNA-chains.
The established by Chentsov and Poljakov (1970) presence of an
especially dense substance in the metaphase and telophase chromosomes
distinguished for its density from the surrounding cytoplasm and chromatin,
called matrix deserves no less attention (Fig. 2–45). According to Baskin
(1995) nuclear matrix is the key to gene expression.
image
Figure 2–45. Matrix in metaphase and telophase chromosomes (After Chentsov and Poljakov, 1970). a — metaphase chromosome after processing the cells with 0.2% of CoCl₂ solution; b — telophase chromosome surrounded by matrix. M — matrix
By the help of the methods for differential staining of chromosomes the
existence of two fractions of chromatin — heterochromatin and euchromatin
— was proven (Fig. 2–46). They differ in a number of qualities and
properties. Heterochromatin remains condensed during the entire interphase
and preserves its capacity for an intense staining, which is typical of
metaphase chromosomes. Brown (1966) has arrived at the conclusion about
the existence of two heterochromatin types — structural and facultative. In