THE SCIENTIFIC MONTHLY 



Frankly, these are questions with which 

 the working geneticist lias not much con- 

 cern himself, except now and then to 

 speculate as to the nature of the postu- 

 lated elements. There is no consensus of 

 opinion amongsl geneticists as to what 

 the genes are — whether they are real or 

 purely fictitious — because at the level at 

 which the genetic experiments lie it does 

 not make the slightest difference whether 

 the gene is a hypothetical unit or whether 

 the gene is a material particle. In either 

 case the unit is associated with a specific 

 chromosome, and can be localized there 

 by purely genetic analysis. Hence, if tne 

 gene is a material unit, it is a piece of a 

 chromosome; if it is a fictitious unit, it 

 must be referred to a definite location in 

 a chromosome — the same place as on the 

 other hypothesis. Therefore, it makes no 

 difference in the actual work in genetics 

 which point of view is taken. 



Between the characters that are used 

 by the geneticist and the genes that the 

 theory postulates lies the whole field of 

 embryonic development, where the prop- 

 erties implicit in the genes become ex- 

 plicit in the protoplasm of the cells. 

 Here we appear to approach a physio- 

 logical problem, but one that is new and 

 strange to the classical physiology of the 

 schools. 



We ascribe certain general properties 

 to the genes, in part from genetic evi- 

 dence and in pari from microscopical ob- 

 servations. These properties we may 

 next consider. 



Since chromosomes divide in such a 

 way that the line of genes is split (each 

 daughter chromosome receiving exactly 

 half of the original line) we can scarcely 

 avoid the inference that the genes divide 

 into exactly equal parts; but just how 

 this takes place is not known. The anal- 

 ogy of cell-division creates a presumption 

 that the gene divides in the same way, 

 but we should not forget that the rela- 

 tively gross process involved in cell-divi- 

 sion may seem quite inadequate to cover 

 the refined separation of the gene into 

 equal halves. As we do not know of any 

 comparable division phenomena in or- 

 ganic molecules, we must also be careful 

 in ascribing a simple molecular constitu- 

 tion to the gene. On the other hand, the 

 elaborate chains of molecules built up in 

 organic material may give us, some day, 

 a better opportunity to picture the mo- 

 lecular or aggregate structure of the gene 

 and furnish a clue concerning its mode of 

 division 



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