Abstract
Multiple-point crosses where 20 pairs of regions (ten loosely linked markers) for the study of contiguous exchanges involving two linkage groups, capable of being investigated at a time, were utilized. In order to find out the effect of a chelating agent on interference, crosses were treated with different molar concentrations of ethylene-diamine tetraacetic acid (EDTA). All marker strains were standardized before use by inbreeding with a wild-type of known parentage. Since tests based on Coefficient of Coincidence and on Poisson distribution for finding out the position interference are rather unsatisfactory, a method based onContingency Chi-square test for detecting the intensity and nature of interference is described. Data obtained from 1813 analyzable ordered tetrads show that positive interference is absent in the control crosses. It is present among certain regions in crosses when treated with 4×10−5M and 10×10−5M EDTA but it vanishes again in crosses when treated with 20×10−5M EDTA. Negative interference is present in the control crosses but it varies among pairs of regions on the two linkage groups. The localization and intensity of interference are alterable with EDTA treatment. The data are discussed in the light of certain concepts invoking to explain the mechanism that involves a genetic exchange.
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