Whittinghill, M. and Hinton, Claude W. (1950) The Nature of Linkage Variation with Age in Inversion Heterozygotes of Drosophila melanogaster. Proceedings of the National Academy of Sciences of the United States of America, 36 (10). pp. 546-551. ISSN 0027-8424 http://resolver.caltech.edu/CaltechAUTHORS:WHIpnas50
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Two kinds of variation in linkage values in Drosophila experiments are well known but poorly understood. One is the change in crossover values with increasing age of the female as shown by Bridges ; the other is excessive variation from female to female as pointed out by Gowen . Studies reported in the present paper on an age effect in a special situation may contribute to the interpretation of both problems. They also serve as controls for the irradiation paper which follows . The chief result of aging is a rapid decrease in recombination values during the first six days of egg-laying, particularly at or near the spindle attachment of the chromosome. After that period smaller changes consist, with variations, of a slight rise and second fall. In recognition of this Bridges  has defined as a condition for chromosome mapping the use of data from young females. From such data inferences are made as to the amount of actual crossing over which has occurred between genes which are assumed to be heterozygous at the time when the germ cells enter meiosis. That this procedure may overestimate the amount of crossing over has been elaborated by the senior author both by reasoning back from observable clustering of the data  and by deducing certain consequences of crossing over premeiotically, in gonial cells . The present experiment shows an age effect and clustering attributable to oogonial crossing over in the same body of data, where meiotic crossovers have been greatly reduced or eliminated by inversions.
|Additional Information:||Copyright © 1950 by the National Academy of Sciences Communicated by J. N. Couch, August 17, 1950 These experiments were substantially aided by a grant from the Carnegie Research Fund of the University of North Carolina during the winter of 1949, for which we are very grateful. For aid in making certain calculations we wish to thank Dr. A. S. Householder, Head of the Mathematics Panel, Oak Ridge National Laboratory. We thank Miss Margaret Stewart of this laboratory for coding the 90 cultures to hide their familial identity.|
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|Deposited On:||27 Nov 2006|
|Last Modified:||26 Dec 2012 09:18|
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