246 The Nature of Biological Diversity 



Whereas it formerly sufficed to think of genes that program the 

 synthesis of specific enzymes, it is now necessary to postulate several 

 categories of genes whose sole purpose is to control and modulate other 

 genes. If this system of control seems unnecessarily complex, one is 

 well advised to reflect on the metabolic pathways for a miniature 

 molecule such as acetic acid. What if the controlling mechanisms of 

 a cell turn out to be as intricate as the "metabolic maps"? 



Microbes versus higher organisms 



The central dogma is based on studies of microbes and their viruses. 

 Therefore, the question may well be asked whether it has any bearing 

 on developmental processes in the higher and more pretentious forms 

 of life. 



At this point I must confess that I find the concept of regulator 

 genes and operator genes — not to mention the rather mysterious 

 "episomes" — strikingly reminiscent of McClintock's genetic "con- 

 trollers," including "activators," "modulators," and "dissociators," 

 which were described in 1951 (for review see Brink, 1958). So, the 

 pertinence of these concepts has already been documented in at least 

 one "higher organism," the corn plant. 



Despite all this duplication in terminology, I believe that the new 

 point of view has much to tell us about the management of genetic 

 information in animal cells and that a judicious application of its 

 principles can promote a great leap in what may prove to be the 

 forward direction. 



As a first and somewhat hesitant step toward this objective, I pro- 

 pose to consider how the new theory, derived largely from studies of 

 bacteria and viruses, may be applied to certain aspects of insect 

 growth and metamorphosis. 



Differential gene activitg 

 in giant chromosomes 



In the banana orchards of Brazil there lives a mosquito-like fly 

 called Rhynchosciara angelae. The female of this insect oviposits a 

 cluster of some 150 eggs, all of which hatch simultaneously a few days 

 later. The larvae then assemble into a compact mass and crawl around 

 together as a slug-like object. 



The lives of the 150 larvae are wonderfully synchronized. Over a 

 period of a month or so, they grow at the same rate, molt at the same 



