The development of modern genetics, A. H. Sturtevant has commented (1965), affords a striking example of the convergence of different disciplines. In the twentieth century it was first cytology that interacted with genetics, and rapid advances in both fields resulted. Subsequently, statistics, practical breeding, evolution theory, immunology, biochemistry, and biophysics all have contributed heavily. From syntheses afforded by this cross-fertilization have come new ideas, techniques, and dramatic developments in genetics as well as in related fields.

This symposium honoring Thomas Hunt Morgan on the centennial of his birth provides an example of the mutual enrichment that results from the interaction...

Dna is perhaps the only molecular constituent of the cell that exists as a single entity which is replicated before division, following which each daughter molecule or chromosome must be carefully distributed into each daughter cell. This duplication and distribution poses a unique problem to the cellular physiologist. How can one entity—not to speak of more than forty—be carefully duplicated and then one copy of each separated into two cells? The problem becomes formidable when one considers that each of these objects is a strand or filament many millimeters long, all of which are coiled into a volume...

Meiosis is the cell division through which the chromosome number of the zygote is reduced to one-half and is the basis of segregation, linkage, and recombination of genes in higher organisms. The essential features of meiosis have been well characterized for more than half a century in terms of chromosome behavior: pairing of homologous chromosomes (synapsis), chiasma formation, and reduction in chromosome number (Rhoades, 1961). Elucidation of these processes at the molecular level in relation to recombination had to wait until recently because of the difficulty of overcoming technical problems in the control of biological systems to obtain meaningful interpretations...

Because of the unique and dominant role played by the genome, the cell is probably more affected by any disruption of covalent bonds in its genome than in any other cell constituent. Any irreparable damage to the dna thread may result in a loss of function and lead to failure in cell reproduction and to cell death. It is hardly surprising, therefore, that cells should have evolved special devices for the preservation of the genome in adverse circumstances, such as when subject to damage by chemical mutagens, or high-energy radiations.

Several mechanisms for reconstructing damaged or fragmented genomes have been...

Genetic information essential to the growth ofEscherichia coliK12 is contained in a continuous linkage group. Physically it appears to be a double-stranded molecule of deoxyribonucleic acid (dna) some 1.3 mm in length. This “chromosome” behaves as a single replicating unit (Cairns, 1963). A growing cell ofE. coliusually contains several such masses of dna (Mason and Powelson, 1956).

Nonessential genetic information may exist as separately replicating units of dna. The fertility factor (F) ofE. coliK12 is an example. When it is present in the cells in an autonomous form the culture is referred to as...

In the spring of 1966 I realized that although I had been teaching for several years about the power of genetics in answering biochemical questions, I had taken little advantage of it in my own research. To remedy that situation, I spent that summer at Cold Spring Harbor, in C. R. Davern’s laboratory, studying the suppression of nonsense mutations in bacterial viruses. Nonsense mutations have been known for a long time, but it was only five years ago that their fundamental nature was described by Benzer and Champe, working on the rII cistrons of bacteriophage T4 (1962), and by Garen...

The formation of individual protein molecules under the control of structural genes is now fairly well understood. Considerably less is known about what is for many proteins the next step: their assembly into more complex supra-molecular aggregates such as multi-enzyme complexes or cellular organelles. If we assume that this process also must be under gene control, then we are faced with the question of how genetic information is used to direct it. For a few simple systems such as the tobacco mosaic virus (Anderer, 1959) and the γ-globulin molecule (Haber, 1964; Whitney and Tanford, 1965), reconstitution experiments have shown that...

It is well known that organisms contain more than a single species of trna for many if not all amino acids. For example, inNeurospora crassa there are at least four leucine trna’s (Barnett and Epler, 1966b) and inEscherichia coli(Weisblum,et al., 1965), at least five. Although the coding properties of multiple trna species have been examined in some detail (Barnett and Epler, 1966b; Weisblum,et al., 1965), their role in the whole of cellular protein synthesis is not completely understood. That is, it is not known whether all trna’s participate in the syntheses of all proteins,...

There is now evidence that the primary feature of processes of determination in embryonic development consists in the production of inactive messenger rnas. Our purpose here is to direct attention to some of this evidence and to related experiments concerning the control of protein synthesis in embryonic development.

The phenomenon of determination in embryonic development is a specification process whereby cells become progressively restricted with respect to their future fate. This process generally takes place without any microscopically visible change. It is detected by certain types of biological experimentation, particularly transplantation or explantation of the cells or tissues. When a...

I remember a time, long ago, when I was a graduate student. As happens to all graduate students, or to most graduate students, I ultimately came to the end of my graduate student career, climaxed by an oral examination. As the chairman of the examining committee, Professor Alfred Henry Sturtevant, sat down, he lit his pipe and said, “Tell me, please, what is your idea of a gene?” Luckily I’ve forgotten what I answered. As a matter of fact, I’ve forgotten all the other questions too and can remember only that first one. But if Professor Sturtevant were to ask...

Just a few days more than ten years ago, we reported to a group of biologists in an overcrowded room at the aibs meetings in Storrs, Connecticut, the results of some experiments that Philip S. Woods, Walter L. Hughes, and I (1957) had just completed, which showed the semi-conservative distribution of dna in chromosomes labeled with tritiated thymidine. This was not only the first experimental evidence indicating that dna might be replicating as predicted by Watson and Crick (1953), but also the beginning of a series of experiments with tritiated thymidine and other nucleosides in autoradiographic studies. These studies have...