It looks like the 98' finding by the committee of scientists and doctors was disputed in 01'. Here is what Wilkopedia has to say on the matter...The Sally Hemings controversy
For more details on this topic, see Sally Hemings and Jefferson DNA Data.
Regarding marriage between blacks and whites, Jefferson wrote that "[t]he amalgamation of whites with blacks produces a degradation to which no lover of his country, no lover of excellence in the human character, can innocently consent."[59] Whether Jefferson fathered children with Sally Hemings is the subject of considerable controversy since Jefferson is often believed to be the father of at least some of the children of his slave. In addition, Hemings was likely the half-sister of Jefferson's deceased wife Martha Wayles Skelton Jefferson. The allegation that Jefferson fathered children with Hemings first gained widespread public attention in 1802, when journalist James T. Callender, wrote in a Richmond newspaper, "...[Jefferson] keeps and for many years has kept, as his concubine, one of his slaves. Her name is Sally." Jefferson never responded publicly about this issue but is said to have denied it in his private correspondence.[60]
A 1998 DNA study concluded that there was a DNA link between some of Hemings descendants and the Jefferson family, but it did not conclusively prove that Jefferson himself was their ancestor. Three studies were released in the early 2000s, following the publication of the DNA evidence. In 2000, the Thomas Jefferson Foundation, which runs Monticello, appointed a multi-disciplinary, nine-member in-house research committee of Ph.D.s and an M.D. to study the matter of the paternity of Hemings's children. The committee concluded "it is very unlikely that any Jefferson other than Thomas Jefferson was the father of [Hemings's six] children."[61]
In 2001, the Thomas Jefferson Heritage Society[62] commissioned a study by an independent 13-member Scholars Commission. The commission concluded that the Jefferson paternity thesis was not persuasive. On April 12, 2001, they issued a report; at 565 pages, it was far longer than the Foundation report, though many of those pages were devoted to a review of the evidence that the Thomas Jefferson Foundation study examined. The conclusion of most of the Scholars Commission was that "the Jefferson-Hemings allegation is by no means proven"; those members' individual conclusions ranged from "serious skepticism about the charge" to "a conviction that it is almost certainly false." The majority suggested the most likely alternative is that Randolph Jefferson, Thomas's younger brother, was the father of Eston. To be honest I knew the Jefferson family disputed the 98' finding I didn't know that they had a committee of similar scientists to back up their claims....