http://www.pubmedcentral.nih.gov/art...?artid=1893020


Downloadable pdf version can be found here:
http://www.genetics.org/cgi/reprint/176/1/351


The study, from 2007, shows that there is 0% overlap in genetic similarity between continental races, whilst the overlap is small when intermediate populations are considered.

It is framed in obscurantist language - the abstract in particular is highly misleading - but the data are good.