WASHINGTON -- In 1850, the elderly master of a South Carolina estate took pen in hand and painstakingly divided up his possessions. Among the spinning wheels, scythes, tablecloths and cattle that he bequeathed to his far-flung heirs was a 6-year-old slave girl valued soon afterward at $475.

In his will, she is described simply as the "negro girl Melvinia." After his death, she was torn away from the people and places she knew and shipped to Georgia. While she was still a teenager, a white man would father her first-born son under circumstances lost in the passage of time.

In the annals of American slavery, this painful story would be utterly unremarkable, save for one reason: This union, consummated some two years before the Civil War, represents the origins of a family line that would extend from rural Georgia, to Birmingham, Ala., to Chicago and, finally, to the White House.

Melvinia Shields, the enslaved and illiterate young girl, and the unknown white man who impregnated her are the great-great-great-grandparents of Michelle Obama, the first lady.

Viewed by many as a powerful symbol of black advancement, Mrs. Obama grew up with only a vague sense of her ancestry, aides and relatives said. During the presidential campaign, the family learned about one paternal great-great-grandfather, a former slave from South Carolina, but the rest of Mrs. Obama's roots were a mystery.

Now the more complete map of Mrs. Obama's ancestors -- including the slave mother, white father and their biracial son, Dolphus T. Shields -- for the first time fully connects the first African-American first lady to the history of slavery, tracing their five-generation journey from bondage to a front-row seat to the presidency.

The findings -- uncovered by Megan Smolenyak, a genealogist, and The New York Times -- substantiate what Mrs. Obama has called longstanding family rumors about a white forebear.

While President Obama's biracial background has drawn considerable attention, his wife's pedigree, which includes American Indian strands, highlights the complicated history of racial intermingling, sometimes born of violence or coercion, that lingers in the bloodlines of many African-Americans. Mrs. Obama and her family declined to comment for this article, aides said, in part because of the personal nature of the subject.

"She is representative of how we have evolved and who we are," said Edward Ball, a historian who discovered that he had black relatives, the descendants of his white slave-owning ancestors, when he researched his memoir, "Slaves in the Family."

"We are not separate tribes of Latinos and whites and blacks in America," Mr. Ball said. "We've all mingled, and we have done so for generations."

The outlines of Mrs. Obama's family history unfolded from 19th century probate records, yellowing marriage licenses, fading photographs and the recollections of elderly women who remember the family. Ms. Smolenyak, who has traced the ancestry of many prominent figures, began studying the first lady's roots in earnest after conducting some preliminary research into Mrs. Obama's ancestry for an article published in The New York Times earlier this year.

Of the dozens of relatives she identified, Ms. Smolenyak said, it was the slave girl who seemed to call out most clearly.

"Out of all Michelle's roots, it's Melvinia who is screaming to be found," she said.

Beginning Oct. 29, more than 400 black genealogists will attend a three-day International Black Genealogy conference at the Allen County Public Library to learn more about searching for their family histories.

Most similar conferences for Irish or German research draw about 100 people. For an ethnic-based conference, the number of participants is huge, said Curt Witcher, genealogy manager for the library.

Participants include the Afro-American Historical and Genealogy Society chapters, special-interest groups of large societies, the Black West Coast Summit groups plus independent black genealogical and historical societies from the United States, Canada and the Caribbean.

Witcher is expecting a large number of participants from Cleveland, Chicago, Indianapolis and other Midwestern cities as well, he said.

Such societies regularly meet on the East Coast or the West Coast. But they have never held a joint conference bringing everyone together in one place, Witcher said.

Some members of these groups were in Fort Wayne several years ago for a different research conference when they began planning for a joint event here. They were impressed with the city, Grand Wayne Center and the library, he said.

But the big draw for coming back was the library’s world-class collection, which includes some of the best sources for African-American research, Witcher said.

For blacks trying to find records of family living before the Civil War when slavery was still legal, genealogy research is a bit more complex. Slaves were often listed as property, which requires searching deeds and property records not just birth, death and marriage records, Witcher said.

During the conference, those interested in their family history will hear and learn from experts on this specialized branch of genealogy. The library will offer extended research hours to accommodate the conference attendees, he said.

The local African/African-American History Museum and the Fort Wayne Chapter of the Links Inc. are hosting the event with the library.