(CNN) -- With a flick of the wrist, James Johnson uses an elongated cotton swab along the inside of his 102-year old mother's cheek.
Mineola Johnson, 102, is the matriarch of the Rand family's African-American descendants.
He's taken the first step in his search for answers to an existential question that plagues a majority of black Americans: Where did my ancestors come from?
For the Johnsons -- cousins of the Rand family, who are featured in "CNN Presents: Black in America" -- the answer arrives in the form of a certificate from African Ancestry Inc., a Maryland-based company that specializes in ancestral DNA testing for black Americans.
For this story, producers for the groundbreaking CNN documentary series facilitated the DNA sampling of matriarch Mineola Johnson to find out more about the Rand family's African roots.
Rand family members say William Harrison "Hal" Rand (1822-1909), a white farmer and slave owner whose great-grandfather emigrated to America from Kent, England, married Sarah Ann "Sallie" Mullens (1820-1893), and fathered the children of Ann Albrooks Rand, a black woman (1836-1907).
Not much is known about Ann Albrooks Rand, but family members speculate that she was a domestic servant, based on U.S. Census data from 1870. See photos of the Rand family members »
Census records indicate that Ann and her children lived near their white half-brothers and -sisters fathered by William H. Rand.
It's a story shared by many African-Americans whose ancestors made the middle passage and were sold into slavery. Slave women often bore children by their white masters, some by force and others as a consequence of a romantic relationship. See the results of the test, along with a Rand family tree »
The "middle passage" refers to the middle leg of a three-part ship voyage during slave-trading times, around 1600 to 1800, when Africans destined for slavery arrived in the Americas as human cargo. They were traded for goods that would then be shipped to Europe, the last leg of the journey.
To find out more about Ann Rand and her African roots, a DNA sample was taken from her closest living relative, great-granddaughter Mineola Johnson.
The results were prepared by Rick Kittles, Ph.D., CEO and founder of African Ancestry Inc., and presented on video during a recent family gathering in Marshall, Texas.
More than a dozen members of the Johnson family and their Rand cousins met at a local church where the pastor is also kin.
The families sat in silence, their eyes fixed on the television screen. Many were anxious and unsure what to expect from the analysis.
Then, from the television monitor, Kittles read the results. Watch Kittles explain the results of the DNA tests »
"The person who took the test, Ms. Mineola Johnson, we isolated the DNA from her swab and were able to determine an identical match among the Mende people from Sierra Leone," Kittles said.
Jaws dropped, and others nodded in acknowledgment. There was a sense of relief; they had a name of a people and a place that was part of their past.
"I feel more enlightened," said Rubystein McGhee, a retired teacher and the family genealogist, who is also a cousin of the Johnsons'. "I knew about Africa but didn't know where we came from."
For the Johnsons and the Rands, it's a profound moment: discovering an ancestral past that has been an enigma.
"It was shocking ... [an] amazing experience that is hard to express," said James Johnson, Mineola's 75-year-old son. "We know where we are, to know the depth of what we know today is truly a historical moment in my life and my whole family's life."
Johnson's results were fairly typical, according to Kittles, who estimates that one-third of his clients can trace their roots to the same region. Kittles believes that it's because what is now Sierra Leone was a common route for the slave trade.
Johnson's DNA sequence was a 99.7 percent match to the Mende people, and Kittles says his database is so large that most clients have a direct match.
"Once we get the sequence -- what we called the DNA profiles from the African-American that is being tested -- we compare that profile to profiles in the database," Kittles explained. "We run through all of those thousands of lineages and look for matches, and most of the time, we find an identical match."
Kittles claims to have a database of more than 25,000 lineages from more than 384 African ethnic groups.
African Ancestry sells two types of DNA kits: one that traces the paternal roots and another that traces the maternal side. Both sell for $349 and are available on the company's Web site. For about $600, clients can test both matrilineal and patrilineal roots.
Kittles estimates that his company has sold 13,000 DNA kits.
However, some experts warn families to read the results from these types of DNA tests with a grain of salt.
"Just like with any science, there are always some limitations. You can't answer all questions, because you can't take one simple test to say everything about a person's DNA," Kittles admitted.
"It's important to understand that these markers we're looking at only tell us about one or two lineages out of the hundreds of lineages we have of people who have contributed to our DNA," he said.
Though it's extensive, Kittles says, African Ancestry's database is not complete and reflects only about 45 percent of the continent of Africa.
Perry Payne, Ph.D., an assistant research professor at George Washington University, says that results from DNA testing such as this can reveal only a fraction of one's African ancestry. But for African-Americans like himself, that fraction "is better than nothing."
Mineola Johnson's DNA type is "a fairly common type found in sub-Saharan Africa," according to Bert Ely, a molecular geneticist and professor at the University of South Carolina. Ely is also a principal investigator for the African-American Roots Project, a nonprofit group that studies the genealogy of black Americans.
After analyzing Johnson's DNA results, Ely speculated that at least 20 groups scattered throughout Africa, including Ghana, Guinea Bissau, Mali and Sierra Leone, share mitochondrial DNA.
Mitochondrial DNA passes unchanged from mother to child, making it useful to trace maternal lineage. Although both sons and daughters inherit mtDNA from their mothers, only daughters can pass mitochondrial DNA to their children.
"What our research has shown ... for about half of the mitochondrial DNA that is researched today, they have exact matches, 100 percent, to other mitochondrial DNA found in several, even more than 20 groups because of there's been a mixing of people within Africa," Ely said.
For example, Ely points to historical evidence that shows massive migrations among people living in Africa. The Mende people were no exception. They didn't always live in Sierra Leone and at some point merged with other ethnic groups.
"This is the prime example of how you can have a match that hits lots of different ethnic groups in lots of different places," Ely said.
Even though DNA testing for African-Americans seems promising, experts say the results could be misleading.
"Sampling today's Mende as opposed to the Mende people that existed during the time of the slave trade is completely different," Ely said. "They are talking about a probability. The most likely thing isn't necessarily the one that happened."
Genealogy is one of the most-searched subjects on the Internet. About 78 percent of Americans are interested in learning more about their roots, according to a February 2007 study by Ancestry.com.
That interest is not lost on African-Americans, descendants of slaves who were robbed of their African past. But why is the interest in the history of black Americans so much more acute?
"Because we have this brick wall we hit when we trace our family history," Kittles said. "This is a tool that allows us to cross the Atlantic and place ourselves somewhere on the shores of Africa."
For Rubystein McGhee, who has kept track of the family's American roots, knowing something about their African heritage is better than nothing.
"It's so wonderful to know something about Ann Albrooks Rand," McGhee said. "This puts some more meaning to our heritage."
CNN's Jack Lyons and Brian Rokus contributed to this report