If you share a block in the same location with several matches you likely share a common ancestor. This is true even if the blocks overlap each other. |
The easiest way to understand the FT DNA autosomal results is to start with a definition of cM. It's a genetic measurement and it measures genetic distance. According to Wikipedia "A centimorgan (cM) is a unit that describes a recombination frequency of 1%. In this way we can measure the genetic distance between two loci, based upon their recombination frequency." When you are using the Chromosome browser at FT DNA the higher the cM number you select the larger the segments will be for comparison. 5 cM and over signifies a relationship, and over 10 cM conclusive proof of a relationship. The shared cM numbers on your match pages present a different indicator. The higher the number of shared cM in the match section of your results signifies a higher likelihood of recombination for the shared block. The higher the likelihood of recombination the more likely your match is a close relative. Lower shared cM numbers mean that segment does not recombine as often so your match may be more distant in time. I found this page at FT DNA to be the best explanation of the whole autosomal DNA process http://www.familytreedna.com/faq/answers/default.aspx?faqid=17
So the most important numbers to remember are:
- The longest block. The longer the block the more likely you are to be related.
- Shared cM. The higher this number the more likely your relationship is recent (closer cousin) a lower number could mean your match shares a more distant relationship with you (more distant cousin).
- The Chromo Browser setting number relates to the size of the shared block. The higher the number you set it to the larger segment will be for comparison to one or more matches. You may share many smaller segments of DNA with someone also, so you can set the browser to show segments as low as 1 cM.
Am I your only match on your mother's side?
ReplyDeleteOops!! Better correct that. I have two. That sounds better. Thanks Nan!
ReplyDeleteThank you so much for this information about cM.
ReplyDelete