. Cytology. Cytology. (b) Figure 6-10. Schematic Representation of Chiasmata Formation Accord- ing to the Duplication Theory Proposed by Belling. Classical Theory In the classical view proposed by Karl Sax in 1932, chiasmata result from alternate opening out between sister (equational) and homologous (reductional) strands with the kinetic loops being always reductional (Figure 6-9 (c)). On this hypothesis, chiasmata do not represent the result of crossing over, but crossing over may result from breakage and rejoining at points of overlap. In this view also, reduction in the number of chiasmata
. Cytology. Cytology. (b) Figure 6-10. Schematic Representation of Chiasmata Formation Accord- ing to the Duplication Theory Proposed by Belling. Classical Theory In the classical view proposed by Karl Sax in 1932, chiasmata result from alternate opening out between sister (equational) and homologous (reductional) strands with the kinetic loops being always reductional (Figure 6-9 (c)). On this hypothesis, chiasmata do not represent the result of crossing over, but crossing over may result from breakage and rejoining at points of overlap. In this view also, reduction in the number of chiasmata should be correlated with increase in crossing over since each crossover represents ehmination of a chiasma. Differential Coniraction Theory Tension set up by differential contraction after pairing may cause breaks at overlaps. This hypothesis is based on measurements which indicate that contraction is greater in paired regions than in those not 154 / CHAPTER 6. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Wilson, G. B. (George Bernard), 1914-; Morrison, John H. (John Herbert), 1927-. New York, Reinhold
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