PAGE-2 (prostate-associated gene 2 protein), also known as P antigen family member 2B, GAGEC2, CT16.4 or GAGEE2, is a 111 amino acid protein that is expressed primarily in testis and belongs to the GAGE family. PAGE-2B (prostate-associated gene 2B protein), also designated putative G antigen family E member 3, P antigen family member 2B, CT16.5 or GAGEE3, also consists of 111 amino acids and is a member of the GAGE family. Both proteins are encoded by genes that map to human chromosome X, which consists of about 153 million base pairs and nearly 1,000 genes. The combination of a X and Y chromosome lead to normal male development while two copies of X lead to normal female development.