96 The Nature of Biological Diversity 



protein molecules have nearly obscured another area of biology that 

 is larger than either of them and, in fact, encompasses both. This is 

 the area best described as developmental biology. I speak today as a 

 devotee and representative of this area. We developmental biologists 

 share with geneticists an interest in gene function, but in addition 

 we are concerned with the regulation of gene function during develop- 

 ment. We, like the biochemists, are also concerned with the properties 

 of protein enzymes since the characteristics of differentiating cells 

 are basically a reflection of the enzymes they contain. But going be- 

 yond the biochemists, we developmental biologists must also investi- 

 gate the mechanisms responsible for initiating, regulating, or stopping 

 protein synthesis in accord with the requirements of the developing 

 cell. Developmental biology, even that portion which focuses on spe- 

 cific proteins, is vast and complex, and productive research in this 

 area has not yet matched the size of the problems. Nevertheless, prog- 

 ress has been made and I shall attempt to synthesize and interpret 

 a variety of data collected from diverse fields but all bearing on the 

 problem of the origin or synthesis of specific proteins in an organism. 

 Genetics and biochemistry will necessarily make the major contribu- 

 tions. 



The prevailing viewpoint today is that the primary structure of a 

 protein — the linear sequence of amino acids — reflects a corresponding 

 sequence of nucleotides in desoxyribonucleic acid (DNA) and ribo- 

 nucleic acid (RNA). A growing body of evidence supports this view; 

 in any event since a general correspondence between genes and 

 proteins is well established, no extensive review of this area would 

 be justified now. However, it may be useful by way of introduction 

 to call attention to the evidence relating genes to the protein hemo- 

 globin in human beings. This is a well-known and often-reviewed sub- 

 ject but provides a good foundation for my later remarks. 



Hemoglobin synthesis 



Hemoglobin is a complex molecule consisting of four polypeptide 

 chains. In the normal adult, two identical a chains combine with a 

 pair of identical ft chains to compose the finished molecule, which 

 thus may be written a 2 ft 2 . Now the a and ft chains are each under 

 separate gene control and mutant forms of each of these two genes 

 have been discovered. Individuals with sickle-cell anemia, for ex- 

 ample, possess a mutant form of the ft gene and synthesize an altered 

 hemoglobin molecule in which valine has replaced glutamic acid at one 

 position in each of the two ft chains ( for review see Conference on 



