46 Nature of the Genetic Material 



gene. This is the fact that mutagenic ultraviolet rays act maximally 

 at the wave length of absorption for DNA. This is an undisputed 

 proof that DNA is involved in the genie functions. But it does not 

 prove that DNA is the genie material, for the fact would also agree 

 with other interpretations (e.g., that DNA is the necessary scaffold- 

 ing). Here again the facts present the same level of information as 

 all the others, with different and equally good possibilities of inter- 

 pretation, an equilibrium which can be shifted only if all groups of 

 relevant facts are taken together and weighed coolly. 



Returning to the Watson-Crick model of DNA structure, I cannot 

 help proposing what looks like a rather wild idea, based upon the 

 assumption that the structure is as claimed. It is independent of the 

 alternative interpretation of DNA function as genie material per se 

 or as a scaffolding for the proteinic genie material because both DNA 

 and protein will remain together somehow during chromosomal 

 maneuvers. If the two chains of the molecule can become independ- 

 ent and re-create their respective partners, it might be assumed that 

 under special conditions they may remain separate or unite again. 

 As only hydrogen bonds are assumed to be involved, this should be 

 a fair assumption. The "wild idea" is that such a separation happens 

 in the preleptotene or postleptotene chromosome, with all other 

 ingredients of the chromosome following the stiff DNA scaffolding. 

 The two chromatids of the synapsing chromosomes would then differ 

 from two ordinary mitotic split halves in containing only the single 

 chains of DNA. Not much imagination is needed to realize that such 

 a fact would at once solve all the major riddles of synapsis including 

 crossing over. It would also explain such atypical features as pre- 

 leptotene doubleness followed by fusion (Kuwada, 1940) and ab- 

 sence of double chromatids in the tetrad lampbrush chromosome. 

 As anybody can draw the detailed consequences of such a "wild 

 idea," this short statement may suffice. 



One indirect contribution to our problem presents some rather 

 remarkable facts. S. Hughes-Schrader (1953) found in mantids two 

 species which are phenotypically indistinguishable but have a com- 

 pletely different karyotype: males have 2n = 21 and 2n = 17, respec- 

 tively. But in the first species the amount of DNA per nucleus is 

 one and a half times that of the other species. Another species with 

 23 chromosomes has one and a haff times as much DNA as a similar 

 one with 33 chromosomes. The conclusion is drawn that DNA cannot 

 be simply the genetic material. 



