Mutants have X-genes which give them superpowers, but they aren't fully separate from normal humans. In the Days of The Future Past movie, sentinels were targeting even normal humans who had a chance of having the mutant gene passed on to their children, grandchildren, or great grandchildren. Meaning that normal humans who can reproduce with other normal humans can have X-genes in suppressed form. But, what happens when X-genes get active? Do mutants remain homo sapiens?
There are lots of possibilities:
They can reproduce with normal homo sapiens. Meaning they are still homo sapiens.
They can reproduce with each other. Meaning mutants are a different species.
They can only reproduce with other mutants who have the same superpowers. Meaning there are many species of mutants.
They can't reproduce. Meaning they are like mules and aren't part of any species.
Which one is true?
Answers from the movies and comics are allowed.