Sex-limited genes, also known as sex-limited traits or sex-specific genes, are genes that are expressed only in one sex or the other. These genes control traits that are unique or more pronounced in males or females, such as beard growth, breast development, or male pattern baldness. Other synonyms for sex-limited genes include sex-linked genes, gonosome-specific genes, and heterochromatic genes. The expression of these genes is regulated by sex hormones, which influence the development and physiology of each sex. Understanding sex-limited genes is essential for studying gender differences in health and disease and developing treatments targeted to specific sex-specific traits.