DNA and Family Trees
By Angelo Coniglio
Contrary to what many believe (and to the disappointment of the ill-informed), DNA tests, in and of themselves, cannot take a sample of one’s genetic material and magically produce a list of ancestors by name and date, going back generation upon generation.
The key to developing that kind of ‘personal ancestry’ is to have hundreds (or thousands, the more the merrier) of donors have their DNA tested, and then compared. The actual ‘family tree’ enhancement comes not from the DNA tests, but from knowledge that may have been compiled by conventional means (I call it ‘paper genealogy’) by one or more donors with matching DNA.
I’ll use some examples from 23andMe to augment my discussion. Other DNA-testing venues are similar. When you register on 23andMe, you (voluntarily) provide important information about yourself: your current residence; ancestral villages; and common family and ancestral surnames. After your DNA is analyzed, 23andMe adds items to your list: ‘Ancestry’ – the geographical place where most of your ‘ancestral composition’ occurred about 500 years ago (mine is ‘Southern Europe’); and codes for the ‘maternal haplogroup’ and ‘paternal haplogroup’ representing some of your ancestors’ whereabouts 5,000 to 25,000 years ago (my haplogroups are, respectively, ‘H3’ and ‘I2b1’).
In addition to classifying a donor by ‘ancestral composition’ of 500 years ago, and identifying his/her ‘haplogroups’ from the distant past, 23andMe provides a list of ‘DNA Relatives’ identified as ’23andMe patrons with a relationship to you.’ This is a list (coded by the participants for privacy) that shows your ‘estimated’ relatives who are in the 23andMe database, from the closest to the most distant. The closest one shown in my case is a ‘1st cousin’ (actually, my great niece, whose percentage of shared DNA is about the same as that of a first cousin). The most distant (#729 on my list) is identified only as a ‘distant cousin’.
Next to each name in the list is the voluntary information that person entered – and here’s the rub: some give (as I do) their own full, uncoded names, as well as a number of ancestral origins and family surnames; others, presumably to protect their privacy, give no name, no ancestral towns, no surnames. Why anyone joins a DNA service and then shares no information is beyond me, because it is that very information which one uses to see whether there are any obvious reasons for assuming a relationship.
Each person in the list, whether they have given much, or only minimal information, can be contacted through 23andMe. I can simply send a message, asking the person to start a protected and private conversation with me, through 23andMe; or I can request that the person share their genome (genetic blueprint) with me. The person can then elect to share their health and genealogical information; or only their genealogical information, or they can decline to share anything.
Those who agree to share information can be selected for comparison,which shows a bar graph of the 23 chromosome pairs, highlighting those segments of certain chromosomes that are an exact match to mine. A measure of DNA length is the ‘centiMorgan’ (cM). Most venues consider matching segments of 7 cM or longer as significant: that is, showing a genetic relationship between two people. Based on the total length of DNA segments shared, the match will be identified as ‘1st Cousin’, ‘5th-8th Cousin’, ‘Distant Relative’, and so on. These relationships are general. “First Cousin’ means ‘this person shares the same amount of DNA with you as a first cousin would’ In actuality then, the match might be your great-niece or great-nephew, or a great-aunt or great-uncle, who share the same amount of DNA as a first cousin.
If two close relatives had their DNA compared, there would be a large number of long segments that matched, in most of the chromosomes. The more distant the relationship, the fewer and shorter the matching segments would be.
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 helpul 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
