A MODIFIED MODEL OF SEGREGATION DISTORTION IN DROSOPHILA MELANOGASTER

[摘要] Elements of the Segregation Distorter (SD) system of Drosophila melanogaster , Sd and Rsp , were analyzed and the following points were established: (1) The model of multiple alleles at the Rsp s locus proposed by MARTIN and HIRAIZUMI (1979) is supported by our observations. (2) A modifier of SD, tentatively symbolized M(SD), was found close to cn ( 2R-57.5 ). (3) Sd heterozygous males were found to show, under certain genotypic condition, almost complete sterility.——Based upon these observations, the following modified model of segregation distortion is proposed: (1) The M(SD) locus produces a multimeric repressor protein that binds to the Rsp locus as a necessary condition for normal spermiogenesis. M(SD) homozygotes produce a repressor M(SD)/M(SD) ; whereas, a homozygote for its normal allele M+(SD) produces a M+(SD)/M+(SD) repressor. M(SD)/M+(SD) heterzygotes produce a M(SD)/M+(SD) repressor. (2) The Sd locus produces a certain product that, like an inducer in the lactose system of E. coli, tends to bind with the repressor complexed with the Rsp locus. This binding disrupts the repressor- Rsp complex, causing Rsp locus to be turned on. The product of Rsp transcription, in turn, results in sperm dysfunction. (3) Rsp i, an allele of Rsp , has a strong complexing affinity with the repressor such that the Rsp i-repressor complex is "resistant" to the inducing activity of Sd product. Rsp s, on the other hand, has a weaker complexing affinity than that of Rsp i, and the degree of affinity varies among different Rsp s alleles.——A possible extension of the above model is discussed.

[学科分类] 医学（综合）