The Chromosome and Its Division 9 



within the chromosome. The biochemist interested in these problems 

 easily forgets that the genetical problems are on the chromosomal 

 level and that facts relating to molecules, even large ones, must be 

 integrated into the structure of the chromosome. 



These facts raise great difficulties for the assumption of individual 

 gene molecules which duplicate by re-creation of their like. Whatever 

 tiie genie material, it is an integral part of the entire chromosome. 

 This means it is a part of a rather compHcated structure which is 

 capable of exact reduphcation. Though chromosomes, especially those 

 of different size, may vary in structural details, we may safely assume 

 that all chromosomes have in common these elements : ( 1 ) ^ chro- 

 monema which is able to change its length by visible coiling and 

 uncoiling, and also able in special cases to undergo molecular un- 

 coiling; (2) a nucleoprotein or chromatin which is part of the 

 chromonema but tends to accumulate at about equal distances along 

 the chromonema as chromomeres of different and typical size which 

 are visible when the chromonema is much uncoiled, as in prepa- 

 chytene chromosomes, or extremely stretched, as in giant chromo- 

 somes; (3) some kind of ground substance between the coils of the 

 chromonema, sometimes called kalymma, which may form an actual 

 membrane that seems to appear and disappear easily; (4) a centro- 

 mere, which is certainly a differentiation of or within the chromonema 

 that may or may not be comparable to other parts of the chromonema 

 (to. call it a gene, as some geneticists do, is rather confusing); (5) 

 nucleolus-forming regions, which again are part of the chromonema 

 structurally, though in some way different from both centromeres and 

 chromomeres. 



This complex structure has the mechanical and optical properties 

 of a visible fiber and therefore must be built of micellae of parallel 

 chain molecules ( Schmidt, 1937, 1941 ) . UnHke an ordinary fiber these 

 micellae cannot be simple polymerized chains of one kind, and they 

 must be integrated somehow into the complicated structure of the 

 whole. A chromosome, therefore, is an organism rather than a fiber, 

 though it has a fibrous structure and is doubly refringent at certain 

 stages. Hence its division can hardly be the fission of bundles of 

 identical micellae or the re-creation of individual molecules at the 

 surface of old ones. The genie material, whatever it is, cannot indi- 

 vidually duplicate by re-creation, but its duplication must be an 

 integral part of the duplication of the entire chromosome. The alluring 

 picture of the template theory meets, therefore, with tremendous 

 difficulties when we try to apply it to the real chromosome and not to 



