TIME-DEPENDENT CHANGES IN GENE CONVERSION IN ASCOBOLUS-IMMERSUS

The stability of conversion frequencies with time was investigated in Ascobolus immersus. There were usually marked reductions in gene conversion frequencies at locus w1 as crosses matured, to about one third of the initial values. This applied to all six w1 alleles tested, irrespective of their molecular nature, and at all temperatures used. Asci dehiscing early from an apothecium had much higher conversion frequencies than those dehiscing late, but there were no differences between apothecia maturing at different times within a cross. Alleles at four loci unlinked to w1 were also tested. All four showed significant changes, though not in all crosses; three loci showed decreases in conversion frequency with time, while one showed an increase. The relative frequencies of different conversion classes often changed with time. These changes appear to result from alterations in locus-specific recombination initiation and in repair of base mispairs in hybrid DNA, not from differential maturation rates of different ascal segregation classes. These effects could cause misinterpretation of quantitative tests of recombination models from gene conversion data.