I have a question. Are these sentences correct?
1. An uncle of Mark's.
2. An uncle of Mark.
To Harry Smith
Are you sure?
The phrase "an uncle of mine" doesn't mean the same as "my uncle"; if you want to avoid the "mine", you have to come up with some periphrasis like "one of my uncles, of which I have several". I have no problem with the possessive here.
(Incidentally, they're not sentences )