P1D: Coffey y-DNA Project: How to read the genealogy/data files


We have two quite large tables of information loaded with testing details, that you can look at and/or print. They cover “Genealogy Detail” and “Data Detail”.


If you have a printer, I recommend you go back one page, call up “Genealogy Detail”, and print it. It will be 5 pages. And having it in hand will help you follow this discussion:


If you flip through, you will find it shows lines for a large number of individuals, organized into multiple groups. The first page, for example, refers to people “Descended from Edward Coffey (thru son John)”. There will be a separate discussion of each such group, see the link “Major Groups” on the previous page.


The first line on the first page is for a gentleman “Luther Coffey”. (Everybody on the page is a “Coffey”, so it only shows his given name, “Luther”). Working from the left, his sample number was 14986, and we’ve called him the “Reference” for this group. And his line then lists each of his Coffey ancestors, finally leading to an “Edward” on the far right. It shows the name, birth year, and birth state for each ancestor.


For every OTHER person on this page, the lines show their ancestral connections back to this same “Edward”. There may be question marks on some of the lines, showing areas where there is some doubt. And the second column shows how each person compares to our “Luther Reference”.


The tests are available for 12-, 25-, 37-, 67- and 111-marker tests. In the second column, a number like “37/37” indicates the person matched Luther on 37 markers out of a 37-marker test – in other words a perfect match at the tested level. For a 37-marker test, anything at or above about “33/37” is solid evidence of a family relationship. All of the people on this page are securely related to each other, and their DNA and other evidence shows without doubt they are descendants of Edward.


Most of our testing is done at FTDNA.COM. There are, however, a few people who were tested on ANCESTRY.COM, which uses a slightly different package of markers. On this page you will see two who match “34/34” on Ancestry, which is also excellent.


The actual DNA test data will be in the “Data Detail” sheet. You can go back and look, and maybe print, if you wish. The full print out will be 12 pages, full of numbers. Just look at the first page, and note that a lot of numbers are shaded in pink. These are the markers that are DIFFERENT from those of our Reference “Luther”. It looks like a lot of differences, but the people on this page are all definitely relatives.  Keep in mind that you are looking at the effect on lines of descent of more than 40 people, who are on average 8 generations removed from Edward, with (on this first page) 37 markers exposed to mutations. This amount of variation is quite normal.