“Why are you participating?” My friend Peg asked. “Are you hoping you are related to the Queen of England?”

No, my aristocratic origins are still cloaked in obscurity. The mtDNA deep ancestry test reveals only which so-called haplogroup my mother’s mother’s mother’s mother, and so on, all the way back, belonged to. I was hoping for-what? I wasn’t sure. Something exotic.

After what seemed an interminably long time, I was informed by email that I am a member of haplogroup H, a distinction I share with almost half the women in Western Europe. I was disappointed but not surprised.

Those were early days. At-home DNA testing kits have taken off. Now I am a member of Ancestry.com. It’s fun, but my ancestral pie chart keeps changing. I recently lost my Finnish Russian ancestral splinter and gained Norwegian. Another member of my family was intrigued to find less than one percent of DNA from Mali, Africa, which Ancestry has since expunged. this brings us to the notorious “one-drop rule.”

I learned about the one-drop rule recently. I was curious about the many celebrities, politicians and experts I see on television every day who are introduced as “black” or “African American,” although most of them are light-skinned.

There are many variations in skin color among the natives of Africa. The Dinka, of South Sudan, are extremely dark-skinned, while the San, of South Africa, are light-skinned. Certainly, a person can be African American and not literally black or brown, but that’s not what I’m talking about.

I wondered why a person is automatically labeled black or African American when he or she is known to have white ancestry.

Maybe, I thought, it has to do with the culture in which this person grew up. But no. Look at Barack Obama.

He is exactly half African and half white. His father, Barack Hussein Obama Sr., was Kenyan. His mother, Ann Dunham, was American, by birth mostly British, with a little Swiss and German mixed in. Obama called her “the dominant figure in my formative years.” He grew up with his mother and her parents, and yet no one ever thinks to call President Obama white, or to overlook his race altogether.

After the Civil War, in the Jim Crow era, the one-drop rule was adopted in the southern states, and from there spread to the rest of the United States. This peculiarly American practice labels an individual’s race as black, originally negro, if the individual has “one drop” of African blood.

As a child, I learned about the gradations of mixed blood-mulatto, quadroon, octoroon, high yellow- from my Southern grandmother, who was born in 1884. She talked a lot about blood. I imagine I was the only one who was listening. She was intelligent and not hateful, but perhaps willfully ignorant, retaining an bewildering acceptance of Confederate slavery and the attitudes that had sustained it. She told me quite blithely that Her Uncle Jesse, a slave owner, had seven white children and seven children by an enslaved woman, all of them educated by his white wife. One of his “mulatto” sons was a friend of Booker T. Washington.

“Smartest child Uncle Jesse ever had,” she was fond of saying.

The research of Arnold K. Ho, a Harvard Ph.D. student in psychology, and James Sidanius, a Harvard professor of psychology and African-American studies, shows that the one-drop rule, or “hypodescent,” is still widely accepted by whites and blacks alike in the United States. Hypodescent refers to the assignment of the lower or minority status to the offspring of a mixed race couple.

Halle Berry, whose mother is white, says that her daughter is black, even though her daughter’s father is white. Berry says that she believes in the one-drop rule.

On the other hand, in an interview with Piers Morgan, Beyonce said “I don’t think people think about my race … that is how I look at people … it’s not about color and race.”

Perhaps Martin Luther King put it best: “I have a dream that my four little children will one day live in a nation where they will not be judged by the color of their skin, but by the content of their character.”

Have a good week.