Also in this case dont
is a substitute for the preposition de. A substitution with de qui
or duquel / de laquelle
/ desquels / desquelles ist only possible if it is used in an non-restricted relative clause. However, this is a special case and dont is to be seen to be the better choice in any way - so, make it easier and assume that also in these cases only dont
is possible.
Examples
Mon oncle est parti aux États-Unis. Marie est la
femme de mon oncle.
My uncle has left for the US. Marie is the wife of my uncle.
Mon oncle, dont
la femme est Marie, est parti aux Etats
Unis.
Mon oncle, de qui la
femme est Marie, est partie aux Etats
Unis.
My uncle, whose wife is Marie, has left for the US.
Mon oncle, dont la femme est partie aux Etats Unis, n' arrive pas à faire la cuisine lui-même.
My uncle, whose wife has left for the US, is not able to do the cooking herself.
Note: There is a difference between de qui / dont on the one side and duquel / de laquelle / desquels / desquelles on the other.
Examples
La femme de qui j' ai reçu les lettres est morte.
La femme dont j' ai reçu les lettres est morte.
a) The woman whose letters I have received is dead.
La femme de laquelle j' ai reçu les lettres est morte.
b) The woman of whom I have received letter is dead.
The difference seems minimal, however, in phrase a) the letter are owned by the woman. In phrase b) the letters were sent by the woman, but not necessarily hers.
