Who is on first?
The who’s / whose dilemma is a close cousin to it’s / its. You can avoid mistakes by remembering that possessive pronouns don’t need apostrophes; contractions do.
Who’s is a contraction of who and is, just as it’s is a contraction of it and is. To show the possessive form of a pronoun, you don’t use an apostrophe. You don’t write hi’s for his or her’s for hers, do you? I hope not! So don’t write who’s when you mean whose.
To help you distinguish whose from who’s, memorize this sentence:
Abbott and Costello, whose “who’s on first” routine still makes me laugh, were gifted comics.
Or simply remember the rule: NO APOSTROPHES IN POSSESSIVE PRONOUNS!