A DNA test can help you narrow down the possibilities. And your talking about ethnicity NOT Nationality. Nationality is where you were born and grew up. Ethnicity comes from your genetic makeup and is passed down through the generations. Now that being said. DNA is by no means an exact science, and while it can point you in the right direction, for instance you may find out that you have certain genetic marker in common with Native American DNA samples the lab doing the testing has in it's data base. It cannot get any closer than that, it cannot tell you that your ancestors were part of a specific tribe. I have done alot of research on DNA testing and put what I found out on a webpage: http://www.coolrogue.net/genealogy/dnate... And to answer another of the comments made by someone else...Yes Mexicans started out as a mix of Spanish and the Indigenous peoples of what is now Mexico.