Also, despite a more common belief, 'Genetic Distance' does not directly correlate with generations. I mean it!
Look how serious I am! In my semi-formal attire! Simply because you and a genetic match share a genetic distance of 1 does not necessarily mean that they are your father.
Genetic distance simply refers to the number of mutations between yourself and another individual. Therefore, the greater the number, the more distant the relationship. A genetic distance of 0 refers to a 'perfect match'.
Genetic Distance or 'Steps' is actually prevalent in all 3 of genetic genealogy's main tests.
Regarding Y-DNA testing, it refers to the amount of Y-DNA markers you do not share with a match. This is easy to interpret in Y-DNA because of comparison charts that are available. When looking at FTDNA's matches, for example, clicking on the small orange box to the right of a match's name will reveal a percentage probability of how distant the match likely is. This is based on number of generations. This data is computed using marker level, genetic distance, and mutation rates of individual markers.
Regarding mtDNA testing within FTDNA, genetic distance is used only at the Coding Region (highest level) of matching. At this level, matches, regardless of genetic distance, can typically go back as many as about 16-24 generations. The greater the genetic distance, the closer to 24 and the smaller, the closer to 16, or even closer.
Regarding Autosomal DNA testing, genetic distance exists only within the context of the size of an individual genetic segment that you share with a match.
This topic, however, does not exist within a vacuum and genetic distance, along with any one factor, must be taken into the context of the subject. If a match has a genetic distance of 4 at 37 markers, the comparison chart may show that the relationship likely goes back as many as 15 generations, when you know he's your 2nd cousin. Everything is about probability, and while it's not likely that your 2nd paternal cousin has a genetic distance of 4 at 37 markers, it's possible. Genetic genealogy is much better at proving things than disproving them. For example, it can't necessarily disprove that you and another person are 12th cousins, but it may be able to prove that there's a relationship there somewhere.
No matter how big of of a genetic distance you wish you shared with your Uncle Jake, your test results show it's actually 0, and your crowded voicemail inbox shows that it's time to invite him for dinner.
Nice articles. I'm interested to hear more. Allow me to be difficult about one thing, though: "Genetic genealogy is much better at proving things than disproving them." That depends. Suppose you and a cousin believe you descend from the same female via an all-female line. You both test your mtdna and either (1) it matches, so you now have some supporting evidence, but have NOT proven it (especially if it's a more common result). Or (2) you do NOT match, and so you have definitively disproven your hypothesis. :)
ReplyDeleteThanks for your input! Your are totally correct, but I meant in terms of not being able to be specific about the exact relationship with matches. It can, for example, prove a relationship, but it cannot disprove the fact that you're 7th cousins, etc. In terms of the ethnic breakdown an autosomal test shows, it can, for example, prove that you have some Native American ancestry but it cannot disprove it (if you show no Native American in your results, it doesn't necessarily mean you have none, just not enough.).
ReplyDeleteIn some examples, such as yours, it can disprove relationships. So, of course, it can do both. I suppose I believe that, in general, it is better at proving things.
Something strange is going on. I read your posting the other day on facebook, about Genetic Distances and when I saw your blog on facebook again today, I wanted to send it to someone else. I clicked on the title "Breaking Genetic Distance" and was taken to a site that told me my computer was infected. It was impossible to shut the site down. I had to use the Task Manager to do it.
ReplyDeleteHi Terry. I'm so sorry! I have been working through the ads I'm setting up on my site and that actually happened to me too. I can assure you that it's just an ad and no harm was done. I'm working on making sure it doesn't happen again, since it is annoying. Please let me know if it happens to you again, and feel free to send the site to someone else!
ReplyDeleteI have 3 mtDNA matches on FtDNA who show genetic distance of 1, yet they do not match on FF. Is that because I am 1/4 AJ and the AJ matches drown them out? Or am I not reading it correctly. I have about 4 more with a genetic distance of 2 who do not show up in FF. The first one listed shows her ancestor as the same name of the furthest ancestor (b. 1800) that I can find. But it's Mary Smith--could be anyone.
ReplyDeleteHi Argie. This would happen for 1 of 2 reasons. First, an mtDNA match with a genetic distance of 1 can be related going back as many as about 18 generations, while a Family Finder match can only go back about 5-6 generations. Second, even a close mtDNA match won't show as a Family Finder match if they do not have Family Finder results. The same theory applies for an mtDNA match at a genetic distance of 2 (but they're likely even more distantly related).
ReplyDeleteWhat does AJ stand for?
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ReplyDeleteEven a 0 distance full mtDNA match only has a 50% chance of the common ancestor being within the last 5 generations. For a 95% probability, you have to allow for the possibility the match was within the last 22 generations. I have been unable to find any confirmed statistics on a genetic distance of 1, but obviously, it would be much more likely to be more distant. (AJ = Askenazi Jew, known for high endogamy)
ReplyDelete