Aberrant meiotic segregations attributable to intragenic events have been analyzed in an unselected sample of 1611 tetrads from three heteroallelic diploids of Saccharomyces cerevisiae. Reciprocal recombination between alleles accounts for only a minor fraction of the total aberrant tetrads, while the majority component is represented by single- and double-site conversions. The frequency of double-site conversion is inversely related to the physical length of the interallelic interval. Since double-site conversions do not yield prototrophs, their occurrence leads to biased estimates of intragenic distances. Conversion is viewed as a process of informational transfer distinct from conventional crossing-over. The implications of the findings for genetic fine structure mapping and evolutionary theory are discussed briefly.