The Chromosome and Its Division 17 



Since kinetosomes of ciliates may grow into fibers which break up into 

 subunits, and since the centromere also is endowed with the faculty 

 of growing into a fiber, the simple breakage into two of a growing 

 centromere is quite possible, though Lwoff's work is more in favor of 

 assuming that strict self-duplication is a basic property of the centro- 

 mere and all its equivalents. 



2. The important point is the relation of the exactly self-dupli- 

 cating genie material to the rest of the chromosome, which is diffi- 

 cult to visualize in the complicated micellar organization of the 

 chromosome, as opposed to a simple string of chain molecules, an 

 ideal abstraction not actually representing the chromosome. It is, 

 however, asserted that at one stage the oocyte chromosome is a single 

 molecular chain. ( See below a discussion of lampbrush chromosomes, 

 but these are not directly comparable to mitotic chromosomes. ) If we 

 compare the chromosome, by analogy, to an organism containing self- 

 duplicating and simply growing parts, we can conceive a process of 

 division very much like that of a ciliate (without the nucleus). This 

 would mean that the cytologically visible division would be actually 

 a simple fission after growth of the chromosome as a cylindrical, fiber- 

 like body. The self-duplicating genie material, however, would behave 

 Hke the kinetosomes in Infusoria: all micellae except a single molecular 

 string would degenerate, and these molecules would duplicate ac- 

 cording to the template model. We could imagine that in the so-called 

 resting nucleus these things take place and the chromosome is stripped 

 down to a single molecular chain of a nucleoprotein. If this were so, 

 chromosome doubling in telophase should not be possible except 

 where telophasic karyomeres have already produced the resting 

 nucleus condition for each individual chromosome. I do not know 

 whether any unassailable cases of chromosome splitting in late ana- 

 phase without karyomeres have been established. 



In mitotic chromosomal division, a field-forming gradient starting 

 from the divided centromere would produce two fields into which the 

 duphcated molecules are drawn and arranged in their proper way by 

 the same type of polarized field forces which produce the regular 

 pattern of the cihate kinetosomes after the "anarchic pattern" follow- 

 ing division. The reproduction of the chromosome, then, requires the 

 following: real division of the amorphic centromere; disintegration of 

 the genie structural elements into units of molecular size; duplication 

 of these units all within the intact amorphic, non-genic material of the 

 chromosome; formation of two fields along the chromosome, and 

 distribution of the duplicates to the fields with proper polarization; 



