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The Symposia, 1933 — 2003

1973:   Chromosome Structure and Function, Vol. XXXVIII

Organizer: James Watson

Table of Contents

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Chromosomes have long fascinated biologists, especially since the second half of the 19th century when advances in microscope design and microscopical techniques laid open the interior of the cell to observation (and frequently mis-observation). By the early part of the 20th century, the cytologists had produced superlative descriptions of the behaviors of chromosomes during mitosis and meiosis in many different organisms. However, as the 1941 Symposium on Genes and Chromosomes: Structure and Organization showed, while chromosomes were known to contain nucleoproteins, little had been discovered about the fine structure of the chromosome. Now, after 32 years, the Symposium topic was again the chromosome.

So much had changed in those 32 years! Participants in the 1973 meeting knew that DNA was at the heart of the chromosome, both structurally and functionally. There were many new, sophisticated techniques for studying chromosomes and chromosome-sized DNA molecules-electron microscopy, autoradiography, ultracentrifugation, X-ray diffraction, electrophoresis and radioactive isotopes. However, while some aspects of structure were known for bacterial and viral chromosomes—supercoiling, for example—eukaryotic chromosomes still looked in the electron microscope "...even at their best something like a bad day at a macaroni factory" (as Hewson Swift put it in his summary).

The new techniques had led to significant advances in studying DNA replication at the chromosome level. DNA spreads in the electron microscope and autoradiography had been used to observe directly (although not dynamically) DNA replication in eukaryotic as well as prokaryotic chromosomes. Some of these pictures were quite remarkable. Some progress had also been made in determining the structural variation of DNA in chromosomes, for

example by locating blocks of tRNA and ribosomal genes, and repetitive sequences had been detected by liquid hybridization techniques in the ultracentrifuge. There was also the beginnings of molecular analysis of genes with the fibroin, hemoglobin and immunoglobulin genes were being analyzed. There were even papers reporting studies of the transcription of genes.

Hewson Swift had recommended that participants who felt that there had been little progress should look back to 1941 to see some progress had been made. But at the end of his summary he pointed out the difficulties ahead. How many hours, he asked, had been spent in studying the lac operon, of some 3 x 104 base pairs? At the same rate, he had calculated, biologists had 105 years ahead of them for studying the human genome! Crystal-ball gazing is dangerous. What Swift could not foresee was the advent of recombinant DNA technology, so that the advances between the 1973 Symposium and that on chromatin in 1977, were greater than those between 1941 and 1973.

Jan A. Witkowski

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