Chromosome condensation in mitosis and meiosis of rye (Secale cereale L.)

Structural investigation and morphometry of meiotic chromosomes by
scanning electron microscopy (in comparison to light microscopy) of
all stages of condensation of meiosis I + II show remarkable
differences during chromosome condensation in mitosis and meiosis I
of rye (Secale cereale) with respect to initiation, mode and degree
of condensation. Mitotic chromosomes condense in a linear fashion,
shorten in length and increase moderately in diameter. In contrast,
in meiosis I, condensation of chromosomes in length and diameter is
a sigmoidal process with a retardation in zygotene and pachytene
and an acceleration from diplotene to diakinesis. The basic
structural components of mitotic chromosomes of rye are ``parallel
fibers{''} and ``chromomeres{''} which become highly compacted in
metaphase. Although chromosome architecture in early prophase of
meiosis seems similar to mitosis in principle, there is no
equivalent stage during transition to metaphase I when chromosomes
condense to a much higher degree and show a characteristic
``smooth{''} surface. No indication was found for helical winding
of chromosomes either in mitosis or in meiosis. Based on
measurements, we propose a mechanism for chromosome dynamics in
mitosis and meiosis, which involves three individual processes: (i)
aggregation of chromatin subdomains into a chromosome filament,
(ii) condensation in length, which involves a progressive increase
in diameter and (iii) separation of chromatids. Copyright (C) 2003
S. Karger AG, Basel.