As used as a male name in the USA,
Zane is derived from the English surname, as explained by "overtheclouds"'s post.
The association with
John is because there is a rare pet form of
Giovanni (Italian form of
John) used in northern Italy which is spelled
Zane. But that would be pronounced in two syllables as something like "Zah-neh", I believe, and so is not really the origin of the first name which rhymes with "sane" and "main".