Restoration to the parental genotype of mismatches formed in recombinant DNA heteroduplex.

Crosses were set up, using the b2 locus of Ascobolus immersus, to detect and measure the restoration of the parental genotype of a chromatid from hetero-duplex. From the results it can be concluded that: (1) restoration occurs, and its frequency is comparable to the frequency of conversion; (2) the relative frequency of conversion and restoration on the two homologous chromatids is that expected if the disparity in conversion to mutant and to wild-type of the marker is caused by the decision whether to excise the mutant or wild-type chain. This decision is the same on both chromatids. However, when all data are pooled, a slight, but significant, excess of conversion over restoration is found. The cause of this in discussed; (3) the absence of an excess of restoration over conversion is taken to imply that, in this system, the length of heteroduplex formed in an event is continuous; (4) these findings support the interpretation of tetrads where a crossover is separated from conversion, that they arise by independent correction giving both conversion and restoration in a heteroduplex tract continuous with the crossover.