Sex Determination in Sciara

Abstract

(1) See summary of cytological and genetic data on pp. 488-490.(2) On the basis of these data the following conclusions are drawn respecting sex determination. (3) 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.(4) Sex of the progeny is determined by the zygotic constitution of the female, Presumably female producing females are Aa, male-producing females aa and males aa in constitution A and a representing either chromosomes or genes.(5) Sex of the individual is determined in the ordinary fashion by a pair of sex chromosomes (XX ~[female], XX [male] ).(6) A and a are probably "in" the X,chromosome or associated with it.(7) "Unisexual" progenies are apparently the result of a selective elimination (inactivation) of sperms, not of zygotes.(8) The "precocious" chromosome is probably not a sex chromosome. (9) The "sex limited" chromosomes are apparently not directly concerned in sex determination.