Because who's and whose sound alike, some writers have trouble using these words correctly. They mistakenly treat the contraction who's as a possessive form because of the apostrophe s.
Solution
Use who's
Use whose
as the contraction of who is
Jenna is the cross-country skier who's (or who is) winning the most races this year.
Who's (or Who is) your dentist?
as the contraction of who has
Who's (or Who has) been eating my chocolate fudge brownies?
as the possessive form of who
Jenna is the cross-country skier whose performance is the most outstanding this year.
Whose cat is sitting on my new car?
These are my snowshoes. Whose are those?
as a possessive form of which
This is a nation whose time has come.
The bicycle whose chain is broken is mine. (that is, the bicycle the chain of which is broken is mine)
Note: Use the possessive whose for people, animals and even things.
Tip
If you can substitute who is (or who has) in your sentence, then who's is correct. In all other cases, use whose.
