Gene conversions and their relation to homologous chromosome pairing

Gene conversion is the non-reciprocal transfer of DNA sequences from one gene to a related gene elsewhere in the genome. Molecular evidence for its occurrence in higher eukaryotes was first described by our laboratory in 1980 in the two linked human foetal gamma-globin genes. Over a kilobase of DNA was converted in this initial example. Other investigators have since described more examples of gene conversion including some in which the sequence that was transferred is much shorter. We have now accumulated evidence for a series of such small gene conversions in the human foetal globin gene pair. The number of small gene conversions that we have been able to detect leads us to suggest that gene conversions are the consequence of a general mechanism whereby DNA strand invasions enable chromosomes to find their homologues during meiosis.