could dna be used to prove citizenship?

I have a friend born in England in the 60's of an English mother & a U.S. serviceman. she has lived in the U.S. since childhood (is a permanent resident alien), and is married to a U.S. citizen

Not sure of the father on the original birth certificate from the U.K.

But she does have a birth certificate issued from the state of California, listing her adopted father, who is american. We understand if she had applied for citizen before the age of 18, it would of been automatic.

My question is, if the man she believes to be her father took a DNA test and was a match, would she be a citizen?

In the interests of accuracy, best bet is to contact a Department of Immigration and Naturalization near you. Heredity doesn't necessarily determine citizenship, especially in recent years with passage of the US Patriot Act and other tightening of immigration laws. Even with conclusive DNA tests, your friend may still need to apply for US citizenship since she's no longer a minor child.

Good luck.

Thanks for the reply.