Meiotic drive in natural populations of Drosophila melanogaster .1. The cytogenetic basis of segregation distortion

Meiotic drive has been defined as a force, potentially capable of altering gene frequencies in natural populations, which somehow depends upon the nature of the meiotic divisions; specifically, when the meiotic divisions are such that the two kinds of gametes from a heterozygote are produced in a ratio different from 1 : 1 ( SANDLER and NOVITSKI 195 7). There have been reported numerous cases which either are, or may be, examples of meiotic drive. These include cases in Drosophila ( GERSHENSON 1928; STURTEVANT and DOBZHANSKY 1936; NOVITSKI 1951 ; NOVITSKI and IRIS SANDLER 1957; LINDSLEY and SANDLER 1958), in maize (RHOADES 1942; LONGLEY 1945), in tobacco (CAMERON and MOAV 1957), and possibly in mice (DUNN 1953) and in man (DUNN 1953; SANDLER and NOVITSKI 1957). The purpose of this paper is to present a first account of the results of a series of studies designed to elucidate the cytogenetic basis of a case of meiotic drive which was discovered in a natural population of D. melanogaster. In this population there has been found a second chromosome locus, located in or near the proximal heterochromatin and called segregation-distorter (symbol, SO), which is recovered much more frequently than its normal allele among the progeny of heterozygous male parents. This phenomenon, to which the name segregation distortion has been applied, (1) has never been found to occur in females, (2) apparently requires synapsis (particularly in the region of the locus in question) in order to operate, and (3) comes about as a result of the failure of sperm carrying the normal allele to be formed or to function normally. The evidence bearing on these, and certain other points, and a cytogenetic model to account for the results are presented below.