What is the sex determination system for insects?

Insects primarily utilize the XX/XO sex determination system, which is characterized by the presence of two sex chromosomes, where females usually possess a pair of X chromosomes (XX), and males have only one X chromosome (XO), lacking a second sex chromosome. In this system, the sex of the offspring is determined by the presence or absence of the second sex chromosome. Females, with their two X chromosomes, develop into the female phenotype, while males, with a single X chromosome and no corresponding sex chromosome, develop into the male phenotype.

This system is particularly observed in several insect groups, including grasshoppers and some moths. It contrasts with other systems like XY/XX, found in mammals, and ZZ/ZW, which is observed in birds, where males and females are defined by different configurations of sex chromosomes in a more complex way. The XX/XO model illustrates a simpler determination, making it a prominent example of how sex can be determined by the chromosomal makeup in certain insect species.