44 Nature of the Genetic Material 



at least, is partly diffusely attached to the chromonema, which means 

 in a single parallel molecular layer, according to Astbury's scheme, 

 and therefore too diluted to be optically visible. We know now, first, 

 that genie reduplication is not involved at this stage (actually the 

 opposite); second, that extrusion of RNA into the cytoplasm prob- 

 ably takes place on a large scale for participation in the cytoplasmic 

 growth; and third, that genie functions are performed in connection 

 with the differentiation of the cytoplasm into zones of different pro- 

 spective fate (predetermination). The immense stretching of the 

 chromonema must have something to do with these functions (see 

 also Guyenot). Since the stretching produces a maximum of active 

 surface which should favor the elaboration of the products of genie 

 action, whatever these are, it sounds reasonable to conclude that 

 these characteristic features are an indication of the genie function 

 of the chromonema. The chromomeres with their accumulation of 

 DNA would then be either a structural feature based upon the 

 conglomeration of the folding chromonema into a whorl, held together 

 by the DNA, or involved somehow in the mechanics of the chromo- 

 some, not in its genie function. Much remains to be learned about 

 these processes, but already they make very improbable the idea 

 that the chromomeres either are the "genes" or contain them (which 

 goes back to Belling) and with this also the idea that DNA alone is 

 the genie material. It must be realized, however, that the law of DNA 

 constancy holds also for the amphibian oocyte. The compHcated con- 

 figurations of the lampbrush chromosome and the visible status of 

 the Feulgen positive material do not change anything quantitatively. 

 It is very difficult at present to put all these facts together in a 

 convincing way without succumbing to one or the other dogmatism. 

 There is still the possibility that the real situation is just the 

 reverse, namely, a proteinic skeleton of the chromosome forming its 

 mechanical backbone to which the real genetic material, the DNA, 

 is attached. This opinion is obviously favored by students of the 

 DNA constancy and by the recent biochemical work. There are more 

 relevant facts which thus far have not been mentioned. Schultz 

 (1941) maintains that with Caspersson's optical method a difference 

 in quantity of DNA can be observed in the salivary band supposed 

 to contain the white locus when the normal form is compared with 

 the white mutant. Most geneticists have been very cautious in 

 accepting this claim, I being one of them, though it must be added 

 that none of the critics worked with Caspersson's method. Recently 

 Schultz (Rudkin, Temin, and Schultz, 1953) returned to the subject 



