Neither Windows or Mac OS X are based on Linux. Mac OS X has Unix underpinnings (BSD, I believe) and Linux has Unix influences and "flavor" but isn't "based" on it.
Windows has never been 'based' on any flavor of Unix, as far as I know. Some things the Windows kernel might do might be similar to Unix or borrowed from Unix but Windows isn't "based" on Unix even though many wish it would be.
Peace...