The nonreciprocal transfer of genetic material from one homologous chromosome to another, thereby converting a normal (wild-type) allele to a mutant allele, or vice versa. It is believed to occur as a result of recombination between DNA strands of sister chromatids following a double-strand breakage in one chromatid and subsequent mismatch repair using the ‘wrong’ DNA strand as template. This mechanism can account for the non-Mendelian segregation of genetic markers that can sometimes be observed, for example, following meiosis in yeast. Loss of wild-type alleles due to gene conversion is also implicated in the initiation of certain hereditary diseases and cancers in humans.