In general, most animal groups possess two sexes, male and female, and reproduce sexually. Accurate sex determination is essential for species that rely on sexual reproduction. Although these species produce the same two sexes, sex-determining mechanisms are highly labile across animal taxa. How have sex-determining mechanisms and their associated genes diversified during evolution? What roles did these genes play prior to acquiring sex-related functions?
To address these questions, we focus on insect lineages that have emerged early in evolution. Specifically, we examine the following topics in these species: (1) the identification of sex-determining genes and (2) the functional analysis of ‘sex-determining’ genes identified in other insects. Based on these analyses and comparisons, we discuss the ‘ancestral states’ of sex-determining mechanisms and genes.