DNA experts have questioned Oprah Winfrey's belief that she is a member of South Africa's Zulu nation.
Winfrey said she felt at home in South Africa
The African-American chat-show host announced during a recent visit to South Africa that she had had a DNA test that had shown her to be a Zulu.
She also told South Africans she felt "at home" in the country.
"I went in search of my roots and had my DNA tested, and I am a Zulu," Ms Winfrey said at a seminar in Johannesburg last week.
Professor Himla Soodyall of South Africa's National Health Laboratory Service said it was likely that Oprah Winfrey would have taken a mitochondrial DNA test.
"This involves tracing only one particular line in a person's ancestry, which passes from mother to all her children but then only transmitted to the next generation by her daughters," she said.
In other words, the test can trace a genetic line of a person only to their mother, their maternal grandmother, and so on, matching only one ancestor in each generation.
Identifying a person on the basis of their DNA can only be done by comparing their DNA results with those of other people who were already tested and their data recorded in a database.
"The conclusion that she had Zulu ancestry would indicate that Oprah's mitochondrial DNA lineage must have had an identical match to someone in the global database who was identified as a Zulu individual," Prof Soodyall said.
Prof Soodyall pointed out, however, that genetic lineages did not correspond precisely to cultural or linguistic groups such as the Zulu nation.
"There is not much to distinguish between various linguistic groups, particularly the different language groups spoken in southern Africa, because they have diversified more recently - perhaps within the past 1,000-1,500 years - than genetic differences which have been evolving in our species for about 150,000 years ago," she said.
The historical movement of people around the African continent makes the situation still more complicated.
This could, however, explain how Ms Winfrey's DNA matched with a sample from a Zulu person, even though most African-Americans have ancestors who have been traced to west Africa as a consequence of the slave trade.
According to most historical accounts, the Zulu nation was consolidated only after the departure of slaves from west Africa to the Americas.
South Africa nevertheless has a special place in Ms Winfrey's heart.
"I'm crazy about the South African accent," she said. "I wish I had been born here."