10 - Sex Determination in Insects

Abstract

Resolving the molecular genetic basis of sex determination in arthropods has applications that potentially could result in improved genetic control programs for pest insects or in useful genetic modifications of beneficial species. Sex determination is studied intensively in D. melanogaster. Sex determination in D. melanogaster has three components—dosage compensation, somatic sexual development, and 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. This ratio determines somatic sex, germline sex, and dosage compensation by regulating functions of sets of regulatory genes. One model suggests that sex determination in all insects is based on modifications of the Drosophila scheme in which sexual development is controlled by a hierarchy of key regulatory genes. At the top of the regulatory cascade is Sex lethal+ (Sxl+), which must be ON to determine a female pathway. If Sxl+ is OFF, a male pathway is the “default” developmental process. Sex, subsequently, is determined by the differential splicing of messenger ribonucleic acids (mRNAs). At the end of the pathway, sex determination is influenced by a deoxyribonucleic acid (DNA) binding regulatory protein coded for by a doublesex+ gene. Although sex determination in arthropods is clearly determined by chromosomal and genetic processes, environment also plays a role in some. Infectious agents, including Wolbachia, Rickettsia, spiroplasmas, and viruses are able to modify sex determination or sex ratio in many arthropods.