mechanism of chiasma maintenance. A study based upon behaviour of acentric fragments produced by crossovers in heterozygous paracentric inversions

Predictions of associations among bridge and fragment elements (produced by the various crossover classes in cells heterozygous for paracentric inversions) differ for three models for the mechanism of chiasma maintenance until anaphase I. These models are: 1) that structural binding may be installed at the positions of crossover sites; 2) that telomeres may replicate or become effectively double very late (anaphase I); and 3) that generalized and persistent sister chromatid cohesiveness may exist. Results of detailed observations in maize microsporocytes from plants heterozygous for three different inversions are not readily explained by the first two models but are consistent with the third model.