The jagged 1 protein encoded by JAG1 is the human homolog of the Drosophilia jagged protein. Human jagged 1 is the ligand for the receptor notch 1, the latter a human homolog of the Drosophilia jagged receptor notch.

Mutations that alter the jagged 1 protein cause Alagille syndrome. Jagged 1 signaling through notch 1 has also been shown to play a role in hematopoiesis.