Researchers and companies are increasingly urging consumers to evaluate historical as well as DNA data when tracing genealogy. Greenspan said that in order to achieve more reliable results, analyzers should look for more than one piece of evidence linking genealogical data. He suggests using DNA data along with the origins of surnames, for instance, to verify lineage.

Harvard professor Gates, who also is host and executive producer of African American Lives and African American Lives 2, which is now showing on PBS, credits Ancestry.com for its efforts in digitizing thousands of archival records and making them available on the Internet. He says the digital format has streamlined the process of tracing one's ancestral roots.

But Gates said that people researching their family tree still must include searches of hard copies of historical records in order to be as thorough as possible. "They should also be prepared to do some old-fashioned archival research," he said.

His new company, AfricanDNA, has recently created a partnership with Family Tree to offer Y-chromosome, mitochondrial, and admixture tests.

Admixture tests examine the percentage of European, African, Asian and Native American ancestry that people have, he said.

Gates said his company has a panel of scholars who are experts in the African slave trade and African history and who review DNA test results to offer their insights on what the information means. He said the partnership operates in a way that can serve as a model to others in the DNA testing industry.

"Often with African-Americans, you'll get two or three identical matches with different people from different African tribes, so some services would just pick one," he said.

The price of researching one's family tree through various companies can run from $99 to more than $800. AfricanDNA charges $189 for its premium testing package, GeneTree offers its most popular test for $149, and Family Tree DNA tests start at $129.

Some companies are making huge profits, Gates said. "There's a lot of price gouging in this area."

Greenspan and Gates also said some companies mislead clients by telling them information that is too exact, when today's available science does not offer such precision, particularly when tracking female lineage.

"Let's say that there is a 70 percent chance that two men would have shared a common male ancestor within the last 300 years," Greenspan said. "The equivalent for females would be a 70 percent chance that two women share a common female ancestor in 3,000 years."

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