The bearing of mutant and cross specificity on the pattern of intragenic recombination

Abstract

Four white-spored allelic mutants ofAscobolus immersuswere used to study the effect of mutant and cross specificity on the recombination pattern in intragenic crosses.In the locus studied no correlation was found between the position of mutants on the map and their basic conversion frequencies. One of the mutants evidently caused an increase of conversion frequency of the two others. Crossing-over in intragenic recombination may be mutant-specific as revealed by using two mutants which give no recombinants when crossed with each other. The frequency of crossing-over was higher in crosses in repulsion than in coupling involving the same pairs of mutants. Polarization observed in two-point crosses was due in some instances predominantly to differences in basic conversion frequencies of the mutants used, and in others to the relative position of the mutated sites. Mutants located in the central part of the studied region were those which converted most frequently in two-point crosses. No reciprocal conversions were observed.A number of recombinant asci resulting from two or more separate but highly correlated recombinational events within a gene were found.