The MacGregor DNA Project exists to answer two questions.
Who are the MacGregors? And where do they come from?
Neither of these questions will be answered absolutely nor immediately since the science behind this is still young and results are still open to discussion.
But, for the very latest results as they arrive, go to: http://www.familytreedna.com/public/MacGregor/
An Introduction to DNA PDF
(courtesy of the MacKenzies)