The study of genetics promises to revolutionize genealogy. That won't happen overnight; it may take a decade or two to accomplish. However, one more indication of the upcoming revolution has just gone online.
"Famous DNA" is a section of a web site operated by the International Society of Genetic Genealogy (ISOGG). As the name implies, "Famous DNA" lists mtDNA (mitochondrial) Haplogroup and mtDNA sequences for famous people in history. By comparing the numbers against your own mtDNA numbers, it is possible to see if you are closely related to these people.
"Closeness" is a relative term; it might be close if the most recent common ancestor was within the past ten or twenty generations. Of course, it is also possible to see how these famous people are related to each other.
The Famous DNA web page just went online within the past few weeks. It features data about the Romanovs (the last Russian royal family) as well as about Marie Antoinette, Jesse James, and Luke the Evangelist (the biblical author of the "Gospel According to Luke" who died circa 150 A.D.), as well as several not-so-famous unnamed prehistoric bodies found in England, Italy, and Peru.
The section that caught my eye is the information about descendants of Sally Hemmings, Genghis Kahn, Colla Uais (a High King of Ireland) and Somerled, the Norse Scot foe of the Vikings. In each case, original evidence from the person is not available, but data can be collected from multiple descendants and probabilities can be calculated. The more descendants tested, the higher the probability of accurate DNA information that can be deduced about the original person.
Will we see pages of "Not So Famous Ancestors' DNA" within the next decade? Will it contain DNA sequences from your immigrant ancestors? Only time will tell. In the meantime, the interesting "Famous DNA" page is available at http://www.isogg.org/famousdna.htm