Females have two X chromosomes and are homogametic, while males have one X and one Y chromosome and are heterogametic. During meiosis, females produce gametes containing one X chromosome, while males produce half X-containing and half Y-containing gametes. Fertilization results in XX females from a female X gamete and either male gamete, and XY males from a male Y gamete combined with a female X gamete. Several conditions can result from abnormalities in sex chromosome number, such as Turner syndrome occurring from XO, and Klinefelter syndrome from XXY.