-gen

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Producer: androgen.
2. n. One that is produced: phosgene.

Wiktionary

1. n. A producer of something, e.g. hydrogen

GNU Webster's 1913

1. A suffix used in scientific words in the sense of producing, generating: as, amphigen, amidogen, halogen.
2. A suffix meaning produced, generated.