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a filamentous structure that is the basis of the chromosome in all stages of the cellular cycle. The chromonema was first detected with a light microscope in the late 19th century in cells of pollen from plants of the genus Tradescantia. In nondividing cells, the chromonema is uncoiled and is discernible only with an electron microscope. During cell division the chromonema is coiled in a tight spiral to provide for the spiralization of the chromosome and forms the chromosome’s characteristic structure, which is visible in a light microscope.
In organisms of various species there are from two to 64 spiraled chromonemata in each chromatid. It was believed in traditional cytology that these spiraled chromonemata formed an inner cylinder that was enclosed in a matrix. In modern cytology, however, the concept of the chromonema is less clearly defined. Most contemporary researchers believe that the chromonema is an elementary deoxyribonucleoprotein (DNP) thread 100–200 angstroms in diameter; opinions differ as to the number of molecules of deoxyribonucleic acid (DNA) in the chromonema’s cross section. To some researchers the chromonema represents a certain stage in the assembling of nucleoprotein threads in chromosomes during cell division, as well as in the heterochromatic areas of the quiescent cell nucleus. This stage is marked by the appearance of threads with a diameter of 0.15–0.20 microns.
REFERENCEChentsov, Iu. S., and V. Iu. Poliakov. Ul’trastruktura kletochnogoiadra. Moscow, 1974.
I. I. KIKNADZE