Variation of crossover association frequencies with various aberrant segregation classes in Ascobolus.

1710 asci exhibiting mendelian or aberrant segregation at the b8 spore colour locus in Ascobolus were analysed from crosses between b8 mutants and the wild type in the presence of linked flanking markers. The frequencies of associated crossing-over were found to vary with the various classes of aberrant segregation and thus for the same allele. The highest crossover associations were found for aberrant 4+4m octads (close to 50%), the lowest for 5:3 post-meiotic segregations (19%), whereas 6:2 octads exhibited intermediary values. These variations are interpreted with respect to the modalities of hybrid DNA distribution (asymmetrical versus symmetrical), and mismatch correction.