STATISTICAL-ANALYSIS OF CHROMATID INTERFERENCE

The nonrandom occurrence of crossovers along a single strand during me iosis can be caused by either chromatid interference, crossover interf erence or both. Although crossover interference has been consistently observed in almost all organisms since the time of the first linkage s tudies, chromatid interference has not been as thoroughly discussed in the literature, and the evidence provided for it is inconsistent. In this paper with virtually no restrictions on the nature of crossover i nterference, we describe the constraints that follow from the assumpti on of no chromatid interference for single spore data. These constrain ts are necessary consequences of the assumption of no chromatid interf erence, but their satisfaction is not sufficient to guarantee no chrom atid interference. Models can be constructed in which chromatid interf erence clearly exists but is not detectable with single spore data. We then extend our analysis to cover tetrad data, which permits more pow erful tests of no chromatid interference. We note that the traditional test of no chromatid interference based on tetrad data does not make full use of the information provided by the data, and we offer a stati stical procedure for testing the no chromatid interference constraints that does make full use of the data. The procedure is then applied to data from several organisms. Although no strong evidence of chromatid interference is found, we do observe an excess of two-strand double r ecombinations, i.e., negative chromatid interference.