When you get your DNA results and view your matches, you will probably see some brand new terminology or terminology which you wished you paid better attention in science class to. So, the purpose about this blog post is to explain the new jargon you will be seeing.
If you look at your matches, it will list your nearest and dearest at the top of the list. On my own matches, the one at the top of my list state;
DNA with my 1st – 2nd cousin (who is actually my 1st cousin, once removed) is 370 cM across 20 segments.
A DNA segment is any continuous run or length of DNA. It is described by the place where it starts and the place where it stops.
We measure how closely two people are related using units of measurement called centimorgans or cM. It is a unit used to measure the probability that a section of DNA will be passed on to a descendant intact (rather than being split into separate segments). One centimorgan represents a one percent chance that a section of DNA will split into separate segments (recombine) within a generation.
Centimorgans are not units of physical distance, but rather, units of probability. In general, the more centimorgans two people share, the more closely related they are.
In my example, my 1st cousin once removed, has 370 centimorgans across 20 segments hence they are higher up my list of close matches than my 2nd cousin who only has 320cm across 20 segments.
A parent and child could share approx. 3,475 centimorgans whilst 3rd cousins only share between 90-180.
If I look further down my list, I can see a 4th to 6th cousin who only has 40 cM across 2 segments. I don’t have a clue who this person is but you can see clearly that they are very distant relations due to the low number of cMs in comparison with my first cousin once removed.
Once you get familiar with the lingo and how to interpret the results, you can go to the next level with a chromosome browser or chromosome view to see exactly which DNA segments are overlapping…. But that’s a whole different ball game and definitely way out of my league at this point.