Genie Control of Development 331 



"At the same tirno an iritr-nsifiod production of cell flijjVj proteins 

 is indicated by the increased incorporation rate of labelled amino 

 acids into the soluble protein fraction. It seems reasonable to suggest 

 that certain microsome populations are induced . , . , by the in- 

 creased mitochondria activity U) a synthesis of specific proteins . . . , 

 needed for the differentiation of the cells. 



"Tl'ie existence of a balanced metabolic interrelationship between 

 populations of microsomes and mitochondria, initiated during the 

 determination period and distributed along gradients, established 

 already diaring oogenesis, Is probably of the utmost importance for a 

 normal development. It is hoped that further experiments will con- 

 tribute to a better understanding of the nuclear and cytoplasmic con- 

 ditions, which influence the growing up of such populations and 

 control their functions." 



This quotation, together with the work of the Brachet school, 

 gives us a good summarization of the work on biochemical embry- 

 ology. But when it comes to translate these morphological and bio- 

 chemical descriptions into terms of genetic control of morphogenesis 

 an embarrassing gap opens. We saw how general embryologists try 

 to bridge it, in a way which appears very unsatisfactory. This is not 

 different when the biochemical embryologist looks at the gap. One of 

 these, Holter (1949), has summarized his conclusions thus: "The indi- 

 cations are that in the stream of chemical and metabolic events that 

 constitute the life of the embryo from fertilization to hatching, the true 

 morphogenetic processes are only like ripples on the surface and their 

 quantitative share in the chemistry of the whole is very small. It 

 seems rather doubtful whether we can hope to reveal the mechanisms 

 which cause those ripples by studying over-all metabolism and general 

 enzyme distribution. We are obtaining very interesting results as to 

 the general biochemistry of the egg and embryo, but the crucial prob- 

 lems of morphogenesis may be beyond the reach of the enzyme 

 chemist." 



This rather pessimistic statement is, indeed, worth considering by 

 the geneticist, who looks to the biochemist for a definite chemical 

 meaning of the rather general statements which the geneticist can 

 make about genie action. We all have been too much influenced by the 

 wish to understand genie action in terms of enzymatic action; this is 

 true from Hagedoom, Troland, and Goldschmidt in the older times to 

 Beadle, Kiihn, Wright, and the biochemists and biochemical embry- 

 ologists in recent times. The quotation above, which is certainly 

 basically right as far as present-day knowledge is concerned (but 



