Amount of DNA vs Number of Matches

A Segment-ology TIDBIT

There are two concepts at work here – each is different – keep them straight and separate. Each in it’s own way can provide insights.

1. Amount of DNA from Ancestors. Although DNA from your Ancestors is random, there is some uniformity. You get exactly 1/2 of your atDNA from each parent; pretty close to 1/4 from each grandparent; about 1/8 from each great grandparent. By the time you get to your 128 5G grandparents, the average will be 1/128 from each one of them (roughly 1 percent), but with each generation past your parents, the deviation from the average increases. Still – the total of all ancestors at any generation will sum to 100 percent. On average you got about 15cM from each 5G grandparent, which may be in one segment or spread over several segments. The companies report that, in general, you will not share enough DNA to match most of your 6th cousins; but we know that you have so many 6th cousins that you will share with many of them – experience shows you will share from 0-21cM with some your 6th cousins. [see The Shared cM Project 2.0 at ]

2.Number of Matches from Ancestors. This depends on several factors: Number of cousins, who tests, endogamy, etc.

A. The number of cousins you have from each Ancestor is directly related to the size of their families leading to the number of their living descendants. Larger families => more cousins => more Matches.

B. Similarly the number of cousins you have from each Ancestor is directly related to how far back that Ancestor is. Distant Ancestors => more cousins => more Matches.

C. Who tests. This may be most pronounced with recent immigration. The more recent an Ancestor immigrates, the fewer number of living descendants in the US, where the highest percentage of atDNA test takers live. Recent immigration => fewer cousins tested => fewer Matches.

D. Endogamy. With endogamy, the amount of shared DNA increases, resulting in many more Matches who otherwise might not have matched. The classic case is Ashkenazi Jews, who tend to get many times the number of Matches others get, and the Matches are in fact somewhat more distant than indicated. This also applies to other endogamous populations. Endogamy => more cousins => more Matches.

Some of my experience and observations

My maternal grandmother was from immigrants to US in 1850s. Roughly 1/4 of my atDNA is from her, and 1/4 of my Chromosome Map has TGs from her line. But, I get relatively few Matches on this 1/4 of my Ancestry, and some of the “gaps” in my Map have no Matches in them at all. When I get only 1 or 2 Matches in a TG on my maternal side, it’s pretty certain they are from my grandmother’s line. The other maternal TGs are from my mother’s paternal side with deep Colonial Virginia roots – they tend to have many Matches.

As the Matches pour in, and are added to my TGs and Chromosome Map, I can see where some TGs have many Matches and must come from distant Ancestors – perhaps at the limits of my Tree, or beyond – so I focus on the closer MRCAs (Most Recent Common Ancestors) which provide pointers. In some cases I’ve found the Ancestor had a Plantation and raised many children.

Some of the other TGs have small to medium numbers of Matches, and where I can find an MRCA, they tend to be smaller Colonial families – folks who moved around a lot; died earlier in life; and/or had few known children who survived.

So as you form TGs, and look at the resulting Chromosome Map, they start to paint a picture…


[22K] Segment-ology: Amount of DNA vs Number of Matches TIDBIT; by Jim Bartlett 20170517

Format for AncestryDNA Notes

A Segment-ology TIDBIT

Here is an example of the format I usually use for AncestryDNA Notes, line by line:

[1] 6C1R: BUTCHER/BUSH > Valentine

[2] Gm 123456 [03F25] 15.1cM

[3] 12.4cM/1Seg

[4] SM: 6 [1 is 4C on BUTCHER]

[5] m5/4/17; mr5/5/17w/Gm#

[6] Added to xls & Notes

[1] is just line number, you don’t need to type that in

6C1R is 6th cousin once removed; 4Cx2 is double 4C

BUTCHER/BUSH is our MRCA surnames > Valentine is the child my Match descends from

Gm is GEDmatch ID

[03F25] is my Triangulated Group ID [Chr 3; F means start in 50-60Mbp range; 25 are first two Ahnentafel numbers of my ancestry to the MRCA – in this case my father and his mother]

15.1cM is cM per GEDmatch

12.4cM is cM per AncestryDNA [almost always smaller]

SM = Shared Matches; then the number of them; then any key info about any of them [in brackets]

M5/4/17 means I posted a message; mr means reply

Added note confirms info was added to my spreadsheet and my Notes on each surname

This info is available by hovering over the little document icon next to each Matches name. It is very useful in its own right to help me keep track of each Match. It is also particularly valuable when reviewing a list of Shared Matches – you can easily see which ones you have notes for and what the notes say. This helps you decide if a group of Shared Matches are grouping around one ancestral line.

I do this pretty religiously for all Matches with Hints; and try to do it for all 4C Matches, too – no time is left for the tens of thousands of other AncestryDNA Matches.

[22I] Segment-ology: Format for AncestryDNA Noteds TIDBITS; by Jim Bartlett

One Segment at a Time

A Segment-ology TIDBIT

The old saying: How do you eat an elephant? One bite at a time. We can, and should, apply this advice to Triangulated Groups and Chromosome Mapping. Take it a TG/segment at a time.

These days, the Matches are pouring in, and it’s easy to get overloaded with data. So I’m setting two goals:

  1. Form one new TG every day
  2. Communicate with the Matches in a TG each day

Each person’s objectives and available time are different, so set the timeframe to suit your own situation (every other day, each week or whatever). The point is to put a goal and plan in place.

There are about 400 TGs spread over my 45 chromosomes. So at one-a-day, it would be March 2018 before I could form every TG for my Dad (I’m just getting started on his chromosome map).  But by then this long ignored project would be done; and his map would provide extremely valuable information for my chromosome map.

And if I send out a small group email (average 10 Matches) to the most significant Matches in a TG every day, it will be March 2018 before I focus on every TG. But two good things will happen: 1) I will have focused on every TG, and worked on the Common Ancestor; and 2) For about every 10-20 emails/messages I send out, I determine a new Common Ancestor. So by March 2018 I’ll have another 200 or so Common Ancestors. [NB: Each CA is not necessarily the correct genetic link for the TG, but they are all genealogy cousins and provide important clues in our quest to “walk the ancestor back” and/or obtain multiple agreements on the TG CA.]

In other words, we reap what we sow – we get a percentage return on the communications we send to Matches – the more we send, the more we get in return.

Again, everyone’s situation is different. All I’m suggesting is to set a goal, and schedule some time for TGs and chromosome mapping. Take a periodic bite out of the atDNA elephant!


[22H] Segment-ology: One Segment at a Time TIDBIT by Jim Bartlett 20170218

Uploading to GEDmatch

A Segment-ology TIDBIT

There are 3 basic steps:

  1. Go to and create an account. Your account is based on your email (so carefully choose the email you’ll want to use), and a password (known only to you – if you forget it, you’ll need to reset the password). You’ll get your own homepage at GEDmatch, which will list any DNA kits you upload and/or any GEDcom.
  2. Go to your DNA company and download your raw DNA data file – note the name of the file and where it is saved (usually your Download folder); leave the file zipped (do not unzip it)
    • AncestryDNA – At “Your DNA Results Summary” page, click on top-right: “Settings” (gear icon); click on “Download Raw DNA Data” TAB and follow their directions, which will involve an email and entering your password again.
    • FamilyTreeDNA – on your main “Dashboard” page, under the Family Finder section is a link: “Download Raw Data” – click on that; and then click on the download arrow for “Build 36 Raw Data Concatenated”.
    • 23andMe – UPDATED (1/20/17) at GEDmatch just click on “23andMe fast and easy” – the process takes about a minute!
  3. Log into GEDmatch and upload your raw DNA data file – in top right box, click on “Generic Upload”; then fill in the form boxes, and be sure to check Yes (the default is No); then in the last row: Click on “Browse” means: Click on “Choose File” button. Do that and navigate in your PC folders to where your raw DNA data file is, and click on it. Then Click on “Upload”. Wait several minutes for the process to complete and give you a statement that it is finished.

Note: you can, and should, also upload a GEDcom file (your family Tree) – on your main GEDmatch homepage, see the link for “Genealogy – Family Trees”.

I hope to see you on GEDmatch!


[22G] Segment-ology: Uploading to GEDmatch TIDBIT by Jim Bartlett 20170119

Walking the Ancestor Back

A segment-ology TIDBIT

Here is an example of walking the ancestor back. I just extended one more generation today, giving four intermediate cousins all in the same line of descent from the CA.

The TG is [14B24] 18-30Mbp about 18cM – [14B24] indicates Chr 14, start in 10-20Mbp area, ahnentafel to CA starts 2-4 – some show this as PP]

The following line of descent is all in VA/WV [the four CAs are bolded]:

Common Ancestor: Sylvester WELCH 1696-1753; 1m 1720 Anne SPENCE: Match KBD at ADNA for 9.9cM is 6C1R

MRCA is son: Sylvester WELCH 1729-1810; m c1752 Jemima CARROLL; Match PDJ at FTDNA for 10.1cM is 5C

Dau: Elizabeth WELCH 1777-1847; m 1797 James FLEMING

MRCA is dau: Sarah FLEMING 1809-1854; m 1827 John H BARTLETT: Match LWA at FTDNA for 16.2cM is 3C

MRCA is son: James V BARTLETT 1836-1920; 1m Elizabeth J NEWLON: Match CK at 23andMe for 54.1cM is 2C1R [this segment overlaps the next TG, too]


Son: James V BARTLETT m Betty V BAKER

Son: jvb jr = me!


A Segment-ology TIDBIT

[22F] Segment-ology: Walking the Ancestor Back TIDBIT by Jim Bartlett 20170103

Save the Clues!

A Segment-ology TIDBIT

In genealogy if we look for Thomas BARTLETT in the census and find three entries with that name, we don’t discard them all if we cannot immediately figure it out. We record them all and look for more evidence. The same concept applies to DNA. Record all the Common Ancestors you find with a Match. Even if the Match is a 2nd cousin (2C), she may also be a 5C or 8C on a different line. One of her shared segments may go back to that more distant ancestor – it’s happened to me! Don’t disregard a “pile up” of shared segments which Triangulate (just because they may be from a very distant ancestor). Science tells us that some of those 7-20cM shared segments will be with closer cousins – it’s happened to me, often. Don’t disregard a distant cousinship beyond 5C with a Common Ancestor. Save the clues. As new Matches come in, you may find supporting evidence for that CA in the TG – it’s happened to me. I have 11 out of 35 Matches, on one TG with the same 7G grandparents (some of them are 6C and 7C, the rest are 8C).


[22E] Segment-ology: Save the Clues TIDBIT by Jim Bartlett 20170103

Only One Comparison Needed to Add a Segment to a TG

A Segment-ology TIDBIT

Start with a list of your overlapping shared segments – they all match you (two triangle legs). Find two of these shared segments that match each other (third triangle leg) to form a Triangulated Group! All the rest of the shared segments in your overlapping segment list need only match one of the shared segments in the TG – any one of them with a good overlap – to be added to the TG. The explanation will take a long blog post with diagrams – but the thrust is that forming a TG basically identifies that segment just as good as trio-phasing. So trust me! If a shared segment doesn’t match the TG, it will match the other, overlapping TG; or it is IBC (it happens for some shared segments under 15cM). As a Quality Control measure, I often make a second comparison – it always matches!


[22D] Segment-ology: Only One Comparison Needed to Add a Segment to a TG TIDBIT by Jim Bartlett 20170101