Sex Determination in Sciara

Abstract

Information, already published, on sex determination in Sciara (Dip-tera) is summarised. Cytologieal data are mainly from 5 spp.; genetic data mainly from 2, S. coprophila Lint. and S. impatiens Joh. The author''s conclusions are: Sex determination (in the broad sense) involves two distinct series of phenomena: (a) determination of the sex of the progeny as a whole, (b) determination of the sex of the individual. Sex of the progeny is determined by the zygotic constitution of the [female]. Presumably, [female]-producing [female][female] are Aa, [male]-producing [female][female] aa and [male][male] aa, A and representing either chromosomes or genes. Sex of the individual is determined by a pair of sex chromosomes (XX [female], XY [male]), A and a are probably "in" the X-chromosome or associated with it. "Unisexual" progenies are apparently the result of a selective elimination (inactivation) of sperms, not of zygotes. The "precocious" chromosome is probably not a sex chromosome. Although the exact role of the "sex limited" chromosomes is unknown, they are apparently not directly concerned in sex determination.