Variation of gene conversion and intragenic recombination frequencies in the genome of Ascobolus immersus.

Eighty mutants in 17 ascospore character genes were studied for their conversion patterns. The correlation between conversion pattern and mutagenic origin, previously found in genes b1 and b2 was extended to all the genes studied. Aberrant 4:4 asci were found in most genes irrespective of their conversion frequency. From gene to gene, the conversion frequency showed an almost 100 times variation. The frequency of intragenic recombination also showed sharp variation from gene to gene. The mean conversion frequency and the maximal intragenic recombination frequency were shown to be highly correlated in 5 genes for which these 2 values are known. This correlation was extended to 12 other genes in other Ascomycetes: Saccharomyces cerevisiae, Schizosaccharomyces pombe, Neurospora, and Sordaria. From this study it is concluded that, 1) the probability of hybrid DNA formation undergoes considerable changes according to the region of the genome; 2) the intragenic recombination frequency primarily reflects the frequency of hybrid DNA formation rather than the physical length of the gene; 3) for a given physical distance on the DNA, a similar fraction of the gene conversion events lead to recombination in the 5 Ascomycetes.