66 



THE CELL AND PROTOPLASM 



not yet know what the lower or upper size- 

 limits of these sections are, as only a few 

 have been analyzed. But eertaixily these 

 sections must have a certain amount of in- 

 dependence within the chromosome (they 

 each contain a number of the known loci) 

 as their actions can be recombined or cov- 

 ered by duplicated segments to a certain, 

 but not yet known, extent. But there are 

 a number of facts known from both these 

 fields which can be interpreted as showing 

 that the independence is only limited, and 

 that the changed action of the sections (the 

 mutant and/or position effect) is in some 

 respects also controlled by the pattern of 

 the whole chromosome. It is extremely 

 probable that these blocks are characterized 

 chemically by something which is a typical 

 ingredient of the general chemical pattern 

 of the chromosome, recurring at many 

 points (model : presence of a definite side- 

 chain). The facts which point to the latter 

 conclusion are usually hidden behind genet- 

 ical terminology. (An elaborate terminol- 

 ogy, deeply driven into the mind of the 

 geneticist, is a great check on progress, be- 

 cause it makes it difficult to think in other 

 terms; the terminology is frequently mis- 

 taken for a basic insight.) If we take 

 Drosophila as an example, the great major- 

 ity of mutants may be divided into a few 

 groups of identical or very similar predomi- 

 nantly pathological action, e.g., shortening 

 of bristles, roughening of eyes, scalloping of 

 wings, intensifying or diluting of eye colors, 

 etc. If this action is localized at different 

 loci, each locus carries a different name for 

 the respective mutants, though they might 

 not be distinguishable at all or only within 

 an overlapping range of variation (if the 

 multiple alleles are included in the com- 

 parison). Only in one case a single name 



has been given to a large group of mutants, 

 the minutes, because a special combination 

 of effects characterize them all. Many ele- 

 mentary facts of this type will assume a 

 very different meaning if reconsidered 

 apart from the theory of the gene. 



These, then, are the facts and the conclus- 

 sions to be derived from them, all pointing 

 in the same direction — the decisive impor- 

 tance of the serial pattern of the chromo- 

 some and its blocks of different sizes (in 

 some respects independent), containing a 

 smaller or larger number of loci. The 

 theory of the particulate gene, as derived 

 from mutation, will have to disappear and 

 make way to a new conception. We have 

 indulged in other places in speculating 

 about a possible chemical model for the new 

 conception. Let us refrain here from such 

 speculation, which certainly would have to 

 run abreast of the actually known facts. 

 The program of this symposium requires 

 to keep in mind the parallel with the devel- 

 opment of knowledge in the physical world. 

 It is my opinion that the classic theory of 

 the gene corresponds to the conception of 

 the indivisible atom of old physics. Genet- 

 ics has outgrown this, I hold, and finds 

 itself in a condition parallel to that of phys- 

 ics immediately before Rutherford. I am 

 sure that our Rutherford stage will soon be 

 reached and then we shall be ready for our 

 Planck and Bohr. I am sure that their 

 model of the hereditary material will be 

 the model of the chromosome and not of the 

 gene. But already at the present point of 

 development the facts must be faced clearly, 

 whether they are considered as welcome or 

 as embarrassing. Nothing is gained by 

 hiding the head in the sand, or by erecting 

 sign-boards "Verboten," or by calling 

 names. 



