THE GENE 28-3 



diminishes the concentration of gene -product (the antigen is not nec- 

 essarily the gene -product) to a point where another equilibrium is 

 established. The genotype always retains the synthetic capacity 

 which makes it potentially capable of reestablishing the first equili- 

 brium under "favorable" environmental conditions. 



Adaptive mechanisms also are explicable on the hypothesis which 

 suggests that the presence of a carbohydrate such as galactose may 

 result in the production of galactozymase by increasing the concen- 

 tration of gene -product to a point where a new equilibrium can be 

 maintained and the presence of galactozymase becomes measurable. 



On the i^ame basis ontogeny may involve a series of adaptive re- 

 actions each of which results in a shift in equilibrium, conditioned 

 by the changed environment which continued multiplication produces. 

 In adaptive mechanisms substrate is required for the contined pro- 

 duction of the enzyme; when the substrate disappears, less enzyme 

 is produced. If the substrate be non- diffusible, a few more steps may 

 be required, but the final result is the same. The fact that an enzyme 

 is produced when the substrate on which it acts appears, explains 



Fig. 28-1 A Diagram Illustrating the Proposed Hypothesis of 

 the Nature of the Gene and the Mechanism of Gene Action. The gene 

 is a region along the chromosome where a series of catalysts are ar- 

 ranged in order. Each catalyst is represented many times about the 

 circumference of the chromosome. This view makes the partition of 

 two genes to each cell a relatively certain event as long as a suf- 

 ficiently large population of catalysts is present at each point on 

 the chromosome. It also makes the delayed expression of phenotypes 

 after irradiation explicable on the assumption that only a small arc 

 of the circle of chromogenes has been affected and that several suc- 

 cessive divisions may be required before the affected region is iso- 

 lated in a single nucleus. The basic chromosome thread provides the 

 locus on which the chromo gene , constituting the catalyst, is held in 

 place. Non-Mende lian heredity may result from transfer of chromogenes 

 from active to deficient loci, converting recessive to dominant genes. 

 Conversely dominant genes may be converted to recessive if the chro- 

 mogenes in a heterozygote are partitioned equally to all loci with 

 the result that an insufficient number is obtained at each locus. 

 The gene product is the result of the orderly action of these enzymes 

 on an initial substance which is probably produced in small amounts 

 in all cells. When substrate appears, it removes enough gene-pro- 

 duct to accelerate its production. The gene product is transferred 

 (along with metaphosphate ) to the nucleolus. Here it is united with 

 ribosenuc leic acid and passed out into the cytoplasm. The gene-pro- 

 duct r ibosenuc leic acid complex corresponds to the B building blocks 

 of Monod (fig. 27-5). In the cytoplasm proteins may unite with the 

 complex to produce the differentiated apoenzyme. Union of apoenzyme, 

 coenzyme and substrate result and the effect of the gene is produced. 



