Disparity of gene conversion in frameshift mutants located in locus b2 of Ascobolus immersus

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Abstract
The frequency of conversion and the disparity in the direction of conversion were studied for 6 frameshift mutants lying in locus b2 of A. immersus and giving more 2 wild type: 6 mutant (2+6m) than 6 wild type: 2 mutant (6+2m) aberrant asci (type B). The frequency of conversion decreased from left to right in the locus. The disparity steadily increased from left to right and then reached a plateau. Frameshift mutants (22) giving more 6+2m than 2+6m aberrant asci (type A) and closely linked to 3 type B mutants were also studied; they showed the same frequency of conversion and the same disparity (but in the opposite direction) as the type B mutant to which they are linked. The polar variation of both the frequency of conversion and the disparity as a function of position were expected on the basis of a previous study of 15 mutants giving postmeiotic segregations and located in locus b2. This variation is assumed to reflect the existence of a preferential region for the initiation of hybrid DNA (HDNA) during recombination and a duality in the distribution of this HDNA, with preponderant asymmetrical HDNA near the starting point and preponderant symmetrical HDNA farther from it.