The Boston Globe has an interesting article written by Vanessa E. Jones that describes the use of DNA to provide proof of one's ancestry, especially for Jewish families and for African-American families.
Quoting from the article, "some academics have complained that it's difficult for African-Americans to use only DNA to pinpoint the particular community they come from in Africa. This is because haplotypes, the DNA profile that provides a particular genetic stamp, can occur across different ethnic groups. By the end of this year, Bruce Jackson, a professor of biotechnology and forensic DNA science at MassBay Community College in Wellesley Hills, hopes to create a model that could help African-Americans successfully discover their own lineages. He'll do so by tracing the migration patterns of the haplotypes of people proven to be Korenbaums [a Jewish family with origins along the Bug River in what was once Poland and is now Belarus]. Since the Korenbaums represent a small sampling of people proven to be related, it is easier to make a model for research."
You can read this interesting article at http://www.boston.com/lifestyle/family/articles/2008/09/23/revealing_hidden_roots/.
My thanks to Laura Prescott for telling me about this article.