Are You My Cousin?
By Angelo Coniglio
After having my DNA tested by 23andMe, registering with the site on-line, and seeing preliminary results, I invited certain of the other participants to share their genomes (genetic ‘blueprints’) with me.
My selection of those I invited was based on several factors: were the person’s ‘haplogroup’ codes similar to mine, indicating common ancestors in the distant past? Were the surnames listed in his/her profile familiar, possibly matching surnames in my direct ancestry? Were the ancestral towns listed the same as mine, or near to them geographically? How close was the indicated relationship?
That last criterion bears deeper consideration. The tests run by 23andMe consider that one’s total genome is represented by a cumulative length of chromosome segments of 7,440 centiMorgans (cM). The combined length of all the matching segments from another person is compared to 7,440, and an approximate percentage of shared DNA is calculated. In theory, then, my child would have a total matching length of 3,720 cM, or 50% of my DNA. To give a feel for the degree of relationships found for me so far, one of the earliest relatives found has a total of 36 cM in two segments, for a shared DNA percentage of 0.48%. That’s less than one-half of one percent! But according to 23andMe, this person is my ‘3rd to 5th cousin.’ That is, the DNA shared is about the same as it would be for a 3rd to 5th cousin.
These numbers may seem miniscule, but consider the following: 50% of my DNA should come from my father, 25% from my grandfather, 12.5% from my great-grandfather, and so on. By the time I’ve counted back seven generations, I have less than one percent of my ggggg-grandfather’s DNA. Because of changes in DNA over the generations due to random mutations, the actual percentage retained from each ancestor may be less than the theoretical amount. So 0.48% shared DNA, from my example above, may mean a relationship as close as a third cousin.
Many folks who have their DNA tested are reluctant to share their names or their ancestors’ surnames and ancestral towns. There are generally two reasons for this: they are concerned about ‘privacy’ and possible identity theft; or, those who have developed their own ‘paper’ family trees are reluctant to make those trees available to others, because of ‘pride of ownership.’ In my view, those who have such concerns shouldn’t bother having their DNA tested, since such reluctance effectively suppresses any interaction with potential relatives.
Generally, for genome comparison, I chose to invite folks who shared ancestral surnames and/or places of origin. My reason is that I feel those people have the greatest chance of having developed a ‘paper’ genealogy that somewhere ‘meshes’ with my own, and in that way I hope to find names, dates and records that I have not yet included in my family tree.
For example: my earliest known Coniglio relative is my 4th-great-grandfather Filippo. From a son’s marriage record, I know he died after 7 January 1770, and was probably born around 1715. I know his wife’s name, Vincenza Ricotta, and the names of five sons: Pasquale, Gaspare, Angelo, Amadeo and Felice; all from Serradifalco, Sicily. Let’s say I find a person, call him Joe, with a very small percentage of matching DNA, but who lists an ancestral town of Serradifalco, with ancestors surnamed Coniglio.
I contact Joe, we share genomes, and in correspondence he tells me he’s the descendant of Giuseppe Coniglio, born in 1740, son of Filippo Coniglio and Vincenza Ricotta. He has their baptism and marriage records, and has found that Filippo’s father was Pasquale Coniglio, born in Serradifalco in 1680. So, by having my DNA tested, and comparing it to a distant relative who had his tested, after inspection of sources and corroboration, I’ve found an extension of my own family tree and the name of my fifth-great-grandfather. DNA testing didn’t extend my ‘tree’, but it gave me the means to do so.
Coniglio is the author of the book The Lady of the Wheel, inspired by his Sicilian research. Order the paperback or the Kindle version at http://bit.ly/SicilianStory
Coniglio’s web page at http://bit.ly/AFCGen has helpful hints on genealogic research. If you have genealogy questions, or would like him to lecture to your club or group, e-mail him at genealogytips@aol.com
