BEADLE AND TATUM 



167 



Beadle and Tatimi found this nein organism i?i Neurospora, and 

 solved both of the difficidties. This mold is easily groivn, repro- 

 duces rapidly asexiially, which assures a plentiful supply of individ- 

 uals of identical genotypes, a?id is excellent 7iiaterial for showing 

 biochemical necessities, by varying the envirojimental supply. A later 

 develop77ient in the techjiicjue has the virtue of demonstrating bio- 

 chemical sequejices in cellular metabolism. As a residt, Neurospora 

 has proveji ijivaluable in both geiietic and biochemical research, ajid 

 another vast area of study has opened up. 



From the standpoint of physio- 

 logical genetics the development and 

 functioning of an organism consist es- 

 sentially of an integrated system of 

 chemical reactions controlled in some 

 manner by genes. It is entirely tenable 

 to suppose that these genes which are 

 themselves a part of the system, con- 

 trol or regulate specific reactions in 

 the system either by acting directly as 

 enzv'mes or by determining the specifi- 

 cities of enzymes.^ Since the compo- 

 nents of such a sv^stem are likely to be 

 interrelated in complex ways, and 

 since the synthesis of the parts of in- 

 dividual genes is presumably depend- 

 ent on the functioning of other genes, 

 it would appear that there must exist 

 orders of directness of gene control 

 ranging from simple one-to-one rela- 

 tions to relations of great complexity. 

 In investigating the roles of genes, the 

 physiological geneticist usually at- 

 tempts to determine the physiological 

 and biochemical bases of already 

 known hereditary traits. This ap- 

 proach, as made in the study of an- 

 thocyanin pigments in plants,^ the 



1 The possibility that genes may act 

 through the mediation of enzymes has been 

 suggested by several authors. See Troland, 

 L. T., A?mr. Nat. 51:321-350, 1917; Wright, 

 S., Genetics 12:530-569, 1927; and Haldane, J. 

 B. S., in Perspectives hi Biochemistry, Cam- 

 bridge Univ. Press, pp. 1-10, 1937, for dis- 

 cussion and references. 



~ Onslow, Scott-Moncrieff and others, see 

 review by Lawrence, W. J. C, and Price, 

 J. R., Biol. Rev. 15:35-58, 1940. 



fermentation of sugars by yeasts ^ and 

 a number of other instances,^ has estab- 

 lished that many biochemical reactions 

 are in fact controlled in specific ways 

 by specific genes. Furthermore, inves- 

 tigations of this type tend to support 

 the assumption that gene and enzyme 

 specificities are of the same order. ^ 

 There are, however, a number of lim- 

 itations inherent in this approach. Per- 

 haps the most serious of these is that 

 the investigator must in general con- 

 fine himself to a study of non-lethal 

 heritable characters. Such characters 

 are likely to involve more or less non- 

 essential so-called "terminal" reac- 

 tions.^ The selection of these for ge- 

 netic study was perhaps responsible 

 for the now rapidly disappearing be- 

 lief that genes are concerned only with 

 the control of "superficial" characters. 

 A second difficulty, not unrelated to 

 the first, is that the standard approach 

 to the problem implies the use of the 

 characters with visible manifestations. 

 Many such characters involve morpho- 

 logical variations, and these are likely 



^VVinge, O. and Laustsen, O., Compt. 



rend. Lab. Carlsberg, Serie physiol. 22:337- 

 352, 1939. 



4 See Goldschmidt, R., Physiological Ge- 

 netics, McGraw-Hill, pp. 1-375, 1939; and 

 Beadle, G. W. and Tatum, E. L., Amer. Nat. 

 75:107-116, 1941, for discussion and refer- 

 ences. 



^ See Sturtevant, A. H. and Beadle, G. W., 

 An Introduction to Genetics, Saunders, pp. 

 1-391, 1931; and Beadle, G. W. and Tatum, 

 E. L., loc. cit., footnote 4. 



