THE cytological examination of chromosomes at meiosis in autotetraploid plants is an important part of the study of chromosome behaviour. Cytological studies have varied in intensity from casual observations at meiosis to meticulous analyses of all configurations observable, including an estimate of the frequency of quadrivalent formation. It is a common belief that the number of quadrivalents formed is governed by : (1) the size of the chromosomes; (2) the chiasma frequency; (3) the existence of localized rather than random chiasmata; (4) an excess number of chromosomes, within a cell, which prevents the physical process of pairing; and (5) genetical control. Several of these factors have been discussed under different aspects, sometimes with a slight change in meaning. For example, the cause of low quadrivalent formation has been related to the paucity of ‘pairing blocks’, the position of the centromeres in chromosomes, and chiasma interference across the centromere1.
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Current concepts of quadrivalent formation can be traced to the original publications of C. D. Darlington et al. For references, see “Recent Advances in Cytology” (Churchill, London, 1937) or “Evolution of Genetic Systems” (Oliver and Boyd, London, 1958).
Morrison, J. W., and Rajhathy, T., Chromosoma (in the press).
Klingstedt, H., Mem. Soc. Fauna Flora Fenn., 12, 194 (1936).
White, M. J. D., “Animal Cytology and Evolution” (Cambridge University Press, 1954).
Kostoff, D., J. Heredity, 31, 33 (1940).
Swanson, C. P., “Cytology and Cytogenetics” (Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 1957).
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