Genetical Interference and Gene Conversion

Abstract

Gene conversion is a phenomenon associated with a high frequency of crossing-over of flanking markers (Mitchell, 1955; Case and Giles, 1964; Fogel and Hurst, 1967). Within a sample of 907 conversion events at four loci in the yeast Saccharomyces cerevisiae, 445 were associated with exchange of bracketing markers (Hurst et al., 1972). The finding that approximately 50% of the conversions were associated with crossing-over applied even when the bracketing alleles were in the same gene as the converted alleles. These results imply a direct relationship between gene conversion and crossing-over. A variety of different models have been proposed to explain recombination as a sequence of molecular events that may result in conversion alone, postmeiotic segregation, or either of these events associated with reciprocal recombination of outside markers (for review see Radding, 1973). A corollary of these models is that a reciprocal recombination event implies the occurrence of a conversion event somewhere between the recombined markers (Fogel and Mortimer, 1969; Paszewski, 1970). However, most and possibly all current models do not address themselves to the question of chiasma interference or the distribution of conversions and/or recombinations in adjacent genetic intervals.