The “fancied” part of the definition of “xenogenesis” helps explain the usage — it’s most often seen in science fiction contexts. It’s a noun that refers to offspring that are very different from the parent. In fictional situations, an alien race might produce a xenogenesis that sends the society in an entirely new direction. The word comes from New Latin, with “xen-” functioning as a synonym for “hetero-” and “genesis” referring to the origin of something.