There are a large number of factors in deciding this. For example, which species each parent was (e.g. mother being the Grey vs. father), what kind of Grey, gender of the offspring, environmental factors, and individual genetics would all affect it.
So the answer is that it would vary- nobody can say for sure what their attributes are as opposed to the human anatomy. Besides, few people, if any at all, have ever seen the offspring of a human and a Grey.
If you ever got a hold of their genome, I'd be happy to set up a bunch of Mendel squares to get you an answer
Just because someone has died doesn't mean that they cease to exist.
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