1. Of which person?
   "whose is this coat?" 
2. Of whom, of which
   "a barn whose red planks have weathered to dark brown"

Sounds like: who's

Encyclopedia: Whose

• down the road
• down the stairs
• down under
• Down's syndrome
• down-and-out
• down-at-heel
• down-at-the-heel
• down-at-the-heels
• down-bow
• down-to-earth
• downbeat
• downbound
• downcast
• downdraft
• downdraught
• downer
• downfall
• downfallen
• downfield
• downgrade
• downhearted
• downheartedness
• downhill
• downiness
• Downing