Developmental Studies on Giant Chromosomes

Abstract

specifically those of translation, reprinting, re-use of illustrations, broadcasting, reproduction by photocopying machine or similar means, and storage in data banks. Under § 54 of the German Copyright Law where copies are made for other than private usc, a fee is payablo to the publisher, the amount of the fee to be determined by agreement with the publisher.The use of general descriptive names, trade names, trade marks ete. in this publication, cven if the former are not especially identified, is not to be raken as a sign that such names, as undcrstood by thc Tradc Marks and Merchandise Marks Act, may accordingly be used frcely by anyone.So great was the impact of the "rediscovery" of poly te ne chromosomes on the genetic study of Drosophila that MORGAN, BRIDGES, and SCHULTZ began their 1935-1936 report to the Carnegie Institute of Washington with the words:"During the past two years the emphasis in the Drosophila work has shifted from analysis by breeding methods to analysis by cytological observations".T. H. MORGAN had returned to embryological studies, interrupted 25 years earlier by Drosophila, and the report was a summary of the work of the other two authors. CA LV IN BRIDGES was preparing detailed chromosome maps and cataloging the breakpoints of genetically known chromosome re arrangements in order to correlate his genetic maps with the new cytological ones. ]ACK SCHULTZ, among other projects, continued his studies on position-effect variegation. He noted variegation of the morphology of the salivary gland chromosome regions known to contain the genes for which mottled effects had been observed.Polytene chromosomes continued to play a prominent role in ]ACK'S thoughts and work for the rest of his life. Thirty years later in the 1965 Brookhaven Symposium we find original work supporting the earlier view that variegation resulted from the inactivation of genes in some cells but not others during development: in this case the development of a puff served as the indicator of activity. The intervening years had included a variety of studies aimed at understanding the phenomenon in terms of the regulation of the synthesis of nucleic acids, beginning in an era when proteins were known to have the range of specificities required of the genetic material.But personal involvement in experimental work directly concerned with polytene chromosomes does not reflect the extent of his influence on matters discussed in this volume, namely the nature and function of the genetic material. His most important writings were preparations of critical analysis of data at hand (of which the 1965 symposium paper was the last and one of the best), indicating where evidence was strong and where weak, but, most important, drawing on a wealth of disciplines varied enough to avoid pitfalls so often associated with "specialization". It was the analysis that appealed to hirn and that he offered; those who looked to his writings for answers were sometimes disappointed by a carefully worded statement balancing VI Jack Schultz evidence ag...