XO, XX, XY, XXY, XYY, XXX, XXXX, XXXY, XXYY, and others have been recorded in humans. In addition there is Swyer syndrome, Chappell syndrome, and mosaicism in which the gonadal phenotype doesn't match the genotype. There are also events during fertilization which can cause an XX zygote to gain the SRY gene from the father. The SRY gene is what initiates male gonad development.

Sex is not binary just because there are two types of sex chromosomes. They can occur in multiple combinations and result in a spectrum of characteristics. Many of those combinations result in infertility, because they result in a loss of reproductive organs and/or indeterminate genitalia