; NATURE OF THE GENETIC EFFECTS 353 



ing gene repetitions, called "duplication," is described on p. 377. Once 

 duplicated, the originally identical genes in the two different positions 

 must from then on undergo separate mutations and thereby gradually 

 become differentiated from one another. By these mechanisms it has 

 been possible for evolution to proceed from the stage of one or a few genes, 

 alike and relatively undifferentiated, and producing little or no accessory 

 material, to that of the great constellations of elaborately differentiated, 

 cooperati^^ely acting genes, surrounded by their exceedingly complicated 

 systems of nucleoplasmic, cytoplasmic, and intercellular products, which 

 are characteristic of present-day higher organisms. 



There is as yet no good evidence concerning the nature of the mechan- 

 ism whereby the genes reproduce themselves, or concerning that whereby 

 they control the other biochemical operations of the cell. As regards the 

 former problem, we do not know what level or levels of synthesis are 

 involved in the building of the gene, i.e., whether the stringing together 

 of amino acids, the formation of higher associations, or the foldings of 

 chains are here concerned. We do not know for sure whether it is the 

 nucleic acid polymers, or the protein constituents, or both, which carry 

 the distinctive gene pattern that determines what pattern shall be repro- 

 duced. However, the evidence for a virtually pure nucleic acid composi- 

 tion of those gene complexes which undergo transference between cells in 

 Pneumococci and certain other bacteria, and which have misleadingly been 

 called "transforming substances," would prove (if confirmed by chemical 

 tests rigorous enough to be generally accepted) that nucleic acid polymers 

 by themseh'es are capable of carrying the characteristic gene patterns and 

 of acting as determiners for these in self-reproduction. 



As regards the problem of gene action on the cell, one line of specula- 

 tion, starting with Driesch in 1894, has been that they act as heterocat- 

 alytic enzymes of the most diverse kinds, thus guiding the course of 

 innumerable reactions. Another line of speculation, originating with 

 de Vries's hypothesis of "intracellular pangenesis" in 1889, has been that, 

 utilizing the same principle as that whereby they reproduce themselves 

 for mitosis, they also produce copies or partial copies of themselves, of 

 protein nature, which, becoming detached, pass out into the protoplasm 

 and there act as heterocatalytic enzymes and/or engage in other reactions, 

 according to the nature of the given gene and of the other attendant mate- 

 rials and circumstances. According to the opinion of some authors, all 

 protein syntheses, and possibly some other syntheses as well, take place 

 only at the site of the gene in the chromosome, by the direct intervention 

 of the gene as a hetero- or autocatalyst; according to others, by the 

 action of gene replicas elsewhere in the cell ; while still others would allow 

 these syntheses to be less immediately dependent on the genes. Cer- 

 tainly the composition of each enzyme and of every other protein and, for 

 that matter, of every other substance produced in the cell, depends upon 



