524 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1962 



nodules (ribosome.s) in the cytoplasm RNA then synthesizes the amino 

 acids of the cell into the proteins and enzymes necessary for the 

 specific function the cell is destined to assume. 



The fertilized egg is the mother cell of her offspring. To each cell 

 is given explicit "instructions" as to just what is to be its role in dupli- 

 cating the form and structure of its immediate ancestor. The bio- 

 chemists are attempting to explain all this, but still it seems one of 

 the most mysterious things in the whole physical realm of nature. As 

 said by Fischberg and Blackler (1961), "Long before men knew any- 

 thing about cells, much less molecules, they were familiar with one of 

 the most tangible mysteries in nature: out of a simple-looking egg 

 emerges a living organism, complete and perfect in every detail and 

 unimaginably complex. Each organ just the right size and in the 

 right place and contains the right kind of cell to carry on its special- 

 ized function. Today we are scarcely less mystified. How does the 

 undifferentiated cell of a cleaving egg turn into a specialized cell of 

 heart, liver, nerve, bone, or muscle?" Needham (1942) gave an ex- 

 haustive review of the status of biochemistry and morphogenesis as of 

 20 years ago, occupying 677 pages based on more than 2,400 citations. 

 Bonner (1962) now gives us an up-to-date account of more recent 

 developments in the biochemistry of the genetic materials. Yet both 

 authors leave us still with the mystery of hoto chemical substances 

 determine and control the development of the egg into an embryo that 

 reproduces the structure of its parents, whether a mouse, a bird, a dog, 

 a man, or an insect. According to Bonner the mechanism of cell 

 differentiation is still unlniown. The biochemists, of course, ardently 

 believe that some day the mystery may be dispelled ; l^ut let us hope this 

 will not be too soon, for when all the facts of life are known, biology 

 will lose its interest. 



The specific factors of heredity we have long been told are bodies 

 called genes, thousands of them distributed along the length of the 

 chromosomes. We might then suppose them to be something like 

 seeds in a pod. However, it appears that not yet has a gene been 

 isolated and studied individually. They are parts of the DNA mole- 

 cules, which the biochemists now regard as the basic material of 

 heredity. That the genes are specific somethings, however, is evident 

 from the fact that changes (mutations) attributed to them are re- 

 flected in hereditary changes in the adult. These changes are the 

 structural variations by which natural selection has evolved new 

 species. The genes of a modern animal, therefore, include those that 

 formed it by mutation, and hence they can reproduce its present 

 structure. 



We should very much like to understand how the chemical DNA, 

 whether of the genes or the chromosome molecules, or both, can influ- 

 ence the proliferating cells to build up an embryo and finally an adult 



