The
X0 sex-determination system is a system that determines the sex of offspring among
grasshoppers,
crickets,
cockroaches, and some other
insects. In this system, there is only one sex chromosome, referred to as X. Males only have one X chromosome (X0), while females have two (XX). The zero (sometimes, the letter O) signifies the lack of a second X. Maternal
gametes always contain an X chromosome, so the sex of the animals' offspring depends on whether a sex chromosome happens to be present in the male gamete. Its
sperm normally contain either one X chromosome or no sex chromosomes at all.