There is no such thing as a UNIX kernel. UNIX is just a certificate from the opengroup (
www.opengroup.org ). Even Microsoft could have Windows become a certified UNIx if they wanted.
MacOSX is based upon BSD which is based upon AT&T's original unix operating system but IIRC they had to remove all of the original code from BSD because of licensing issues. So:
MacOSX is not UNIX.