Teo got me reading about this subject a couple of years ago... sent me into days of fascinating history reading.
http://www.bloomberg.com/news/2013-10-08/founding-mothers-of-ashkenazi-jews-may-be-converts-study-finds.html
http://www.bloomberg.com/news/2013-10-08/founding-mothers-of-ashkenazi-jews-may-be-converts-study-finds.html