CHROMATIN IN DIAPAUSE OF THE SILKWORM BOMBYX MORI L.:
THERMAL PARTHENOGENESIS AND NORMAL DEVELOPMENT
V. V. Klymenko, Liang Haoyouan
Department of Biology, V.N. Karazin Kharkov National University, Ukraine;
e-mail: stemway@gmail.com
Having used hematoxylin as a stain, some features of silkworm embryo chromatin in diapause have been
studied in normal and parthenogenetic development. With found direct correlation between the number of interphase
chromatin grains and the number of chromosomes in the nucleus, we examined cell polyploidization in
the embryo at diapause stage. Polyploidization by parthenogenesis is not reducible to endomitotic doubling of
the chromosome set because it comprises 6n-nuclei. Explanation of more diverse range of polyploid cells in
parthenogenesis needs to consider the fusion of cleavage nuclei that is carried out by the cytoplasmic karyogamic
mechanism in the absence of fertilization. For the first time on squash preparations, in diapausing embryo,
we have identified primary germ cells (PGC) that are characterized by less compact chromatin, especially in the
zygotic form of development, a larger size of the nucleus and cytoplasm, and irregular number and size of nucleoli.
Evaluation of PGC ploidy in parthenogenesis by calculation of «loose» chromatin grains in diapause is possible
and testifies polyploidization in embryo germ-line. This explains the inevitable admixture of tetraploid
eggs in diploid parthenoclone grain and its absence in normal development. Cytological method used has revealed
a spiral arrangement of chromatin grains on the inner surface of the nucleus at different levels of ploidy.
Key words: interphase, heterochromatin, bisexual development, parthenogenesis, somatic polyploidization,
germ-line, silkworm, polyploidy, diapause
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