Simplify the following text for a Grade 11 native English-speaking person.
Original: The movie is partially based on two X-Men comic book stories : writer Chris Claremont 's and artist John Byrne 's `` Dark Phoenix Saga '' in The Uncanny X-Men ( 1980 ) and writer Joss Whedon 's and artist John Cassaday 's six-issue `` Gifted '' story in Astonishing X-Men ( 2004 ) .
Simplified: The film is loosely based on two X-Men comic book story arcs : writer Chris Claremont 's and artist John Byrne 's `` The Dark Phoenix Saga '' and writer Joss Whedon 's and artist John Cassaday 's six-issue `` Gifted '' arc .