Chapter 10 - Sex Determination in Insects

Abstract

Resolving the molecular genetic basis of sex determination in arthropods has applied applications that potentially could result in improved genetic-control programs for pest insects or in useful genetic modifications of beneficial species. Sex determination has been studied extensively in Drosophila melanogaster. Sex determination in D. melanogaster has three components: 1) dosage compensation, 2) somatic-sexual development, and 3) germ-line sexual development. The primary cue for determining sex in D. melanogaster is the number of X chromosomes relative to autosomes (A) in a cell (X:A ratio). This ratio determines somatic sex, germ-line sex, and dosage compensation by regulating the functions of sets of regulatory genes. One model suggested that sex determination in all insects is based on modifications of the Drosophila scheme in which a hierarchy of key regulatory genes control sexual development. At the top of the regulatory cascade is Sex lethal+ (Sxl+), which must be ON to determine the female pathway. If Sxl+ is OFF, the male pathway is the “default” developmental process. Sex subsequently is determined by the differential splicing of messenger RNAs. At the end of the pathway, a DNA-binding regulatory protein coded for by the doublesex+ gene influences sex determination. Although sex determination in arthropods is clearly determined by chromosomal and genetic processes, environment also plays a role in some. Furthermore microorganisms, including Wolbachia, Rickettsia, Cardinium, Spiroplasma, and viruses, are able to modify sex determination or sex ratio in many arthropods.