The effects of ultracentrifuging upon the meiotic chromosomes of the male grasshopper, Melanoplus differentialis

✍ Scribed by H. W. Beams

• Publisher: John Wiley and Sons
• Year: 1948
• Tongue: English
• Weight: 886 KB
• Volume: 83
• Category: Article
• ISSN: 0362-2525
• DOI: 10.1002/jmor.1050830105

✦ Synopsis

It is well known tliat the relative specific gravity of the nucleus a s a whole is usually greater than that of the surrounding cytoplasm. The components of the nucleus too have been observed to layer out under the action of relatively high centrifugal force. Usually the neucleoli and chromatin are displaced centrifugally, thus proving thein to be the heaviest eomponents. I n dividing cells the condensed chromosomes a r e often displaced to the centrifugal end, frequently resulting in a striking distortion of the mitotic spindle. I n extreme eases they have been observed torn free of the spindle elements (Beams and King, '36a).

Recent investigations on the structure of chromosomes, particularly in plants, indicate that they a r e not of a homogeneous structure but a r e composed of (1) a middle portion, the chromonemata which presumably bears the genes, ( 2 ) a questionable matrix which may or may not stain with chromatin dyes, (3) a pellicle or membrane which according to Metz ('34) is a differentiated layer which insulates the cliromosomes from one another as well as from other components of the cell, and (4) a kinetochore, a region of the chromosome which is thought to be of fundamental importance in chromo-'Aided by a grant from the Rockefeller Foundation for work on Cellular Physiology.