It surprises some people to learn that both who and which can take the possessive form whose. Some will argue that of which is a better construction when talking about things rather than people, but this results in unnecessary awkwardness. The truth is that whose has been widely and correctly applied to nonhumans for hundreds of years.
Relative clauses are also sometimes referred to as adjective clauses, because they identify or give us additional information about the subject of the independent clause they relate to. Like adjectives, these clauses in some way describe that subject. Relative pronouns, like conjunctions, are words that join clauses—in this case, a relative clause to its main clause. The type of relative pronoun used depends on what kind of noun is being described.
