Expressed in placenta, testis and pituitary. Encoded by a cluster of genes that have evolved by duplication from LHB. HCG-beta is encoded by six non-allelic genes (CGB) clustered on chromosome 19q13.3 and named CGB1, CGB2, CGB3, CGB5, CGB7 and CGB8. Two specific hCGb proteins that differ by three amino acids in positions 2,4 and 117 have been described: type 1 (CGB7) and type 2 (CGB3, CGB5, CGB8). The CGB gene first arose in the common ancestor of the anthropoid primates. Belongs to the glycoprotein hormones subunit beta family.