TG SUMMARY Spreadsheet

This is my ultimate spreadsheet, so far. I think it’s use will be profound.

The spreadsheet and data are pretty simple. Here are the header titles:

Side – Paternal or Maternal [I use Ahnentafel number 2 or 3]

Chr – Chromosome number (1 to 23)

Start – the Start location of each Triangulated Group (TG) use Mbp with one decimal

End – the end location of each TG (Mbp) NB: End of one TG = Start of next TG

Mbp – calculate End minus Start; this is “roughly” the cM (real cM is too hard to calculate)

TG-ID – An ID for each TG – Example 01S2 – on Chr 01, Start ~130Mbp, on 2 side

                For more see: Shorthand ID for TGs

G2 – second generation back, column for Ahentafel number for my Ancestor

G3 – Ahnentafel for one of my grandparents; similar for other generations below








CZN – Cousinship of Most Distant Common Ancestor (MDCA) in this TG [within reason]

MDCA – the surnames of the MDCA Couple Ex: SNIDER/BRITZ

Remarks – a place for any discussion I want about a TG – I could write a book in this cell.

For the spreadsheet header, just type in the above list (to the left of the hyphen) across the top row.

This simple spreadsheet has two parts:

1. Side|Chr|Start|End|Mbp|TG-ID – this describes each TG. I have 372 TGs so my TG Summary Spreadsheet has 372 rows of data. Having already done segment Triangulation of all my Matches at FTDNA, 23andMe, MyHeritage and GEDmatch, this part of the TG summary was a snap. And these data points remain fairly static. I say “fairly” as from time to time, as new Shared DNA Segments are found and new MRCAs determined, I do make minor TG end-point shifts and/or combine or split existing TGs.

2. G2-G10|CZN|MDCA – this part summarizes the genealogy – the Most Recent Common Ancestors (MRCAs) I have with Matches in the TG; and my best, conservative, judgment of what is the MDCA for the whole TG, so far. For each of the reasonable MRCAs in this line I enter the Ahnentafel number of the MRCA – bolded and yellow-highlighted – under the appropriate Generation. See the Figures below. This represents the data that I’m comfortable with. The goal is to Walk the Ancestor Back in each TG, and/or to find multiple, separate Matches who agree with the Ancestral line. In some cases, where I have sufficient evidence, I underline the Ahnentafel numbers to indicate I’m confident with the result. In the other cases the Ahnentafel numbers are clues, and more data is needed. In some TGs I have no MRCA, yet. In just a few TGs (less than 10), there are no Match-segments (beyond very close relatives) – these are small gaps in the overall Chromosome Map.

Both of the two parts above come from my atDNA Master Spreadsheet which has all my Shared DNA Segments with Matches. That spreadsheet is now over 20,000 rows – this TG Summary spreadsheet is 372 rows which I can print out in two pages back to back. A very handy scrap of paper.

This is the spreadsheet version of DNA Painter. In fact I once painted the 372 TGs. And I did the same with Kitty Cooper’s Chromosome Painter program.

Several  observations about this TG Summary Spreadsheet:

1. It is a summary! It extracts the important essence from 20,000 rows of data into 372 rows.

2. Trends – By bolding and highlighting my Ahnentafel numbers I can readily see trends and/or conflicts.

3. Pointers – For TGs with strong evidence of an MRCA, this information is very valuable in looking at other Match Trees in the TG. *Knowing* the TG MRCA is a powerful pointer, which has helped me find MRCAs with many more Matches (including those with only one Ancestor in their “Tree”). This summary has become a powerful TOOL in this respect.

4. Fill-in – In many cases, based on high confidence MRCA Ahnentafels, it is easy to “fill in” the other Ahnentafel numbers leading up to the TG MRCA – these “fill ins” identify the Ancestors who “had to be there” for the DNA to pass down to me.

5. Crossover points – With “filled in” Ahnentafels, it’s easy to see where the crossovers occurred between TGs in a Chromosome. If one TG row has Ahnentafels 2-5-10-21-42 and the next row has 2-5-10-20-40, it’s easy to see the crossover occurred between 21 and 20. In this case, Ancestor 10 had these two adjacent TGs in their DNA – one from his mother (21) and one from his father (20), which he (10) recombined and passed as a single, larger TG segment to his daughter 5. A first cousin (1C) might share that larger segment with me. And, of course, parent 2, would have also passed that *double* segment to me intact as part of that Chromosome. In other words, as we fill out the MRCA Ahnentafels, we can track the crossover points, generation by generation.

6. Crossover points per generation – This also gives us the ability to easily count the crossovers per generation. Will we see the 27 male vs 41 female distribution? On the paternal side we can see how many times the TGs shifted from 4 to 5 (or 5 to 4) [no matter what distant MRCA each of those TGs eventually went to after that]. How many 8 to 9 and 10 to 11 cross overs will there be – will it stay near 27 or tread toward the 34 average?

7. Quality Control – The Crossover points per generation summary may be a good QC check – if our result from the TG Summary Spreadsheet is reasonable. If my TG summary shows a lot of change between TGs, I might show 50 or 60 crossovers in a generation – that seems unreasonable to me, and I would be looking over my TGs. It would be relatively unusual for a Chromosome to shift from one grandparent to another and then back again several times on one Chromosome – it’s more likely that I had several MRCAs in a TG and selected the wrong one.

8. Predictive – I have some TGs with no or a very close (2C) MRCA. In some cases, it’s where much of the Chromosome is from one grandparent. If one TG in the middle is from the other grandparent, that adds two crossovers to the total. Although I’m pulled toward the parsimonious solution, I have to ALWAYS keep from jumping to a conclusion. On the other hand, if my total crossovers for the generation is high, I need to look hard for errors I might have made.

9. Brick Walls – In some TGs I have several Matches at, say, the 4C level, and a lot of other Matches, some with good Trees, but no MRCA beyond 4C level. All other things being equal, I should have some 5C and 6C Matches in that TG (I have ThruLines Matches at Ancestrycom for all of my known 6C Ancestors, so I know the genealogy is there if the TG was really from one of them). So I conclude that those TGs are probably headed past the 4C level and on through a Brick Wall. I’ve used this conclusion to successfully use Match Trees to find a Common Ancestor in two TGs with Brick Walls; and in one case where I had an incorrect Ancestor. Where there are a lot of Matches in a TG with closer Cousins, I am suspicious of an Ancestor I haven’t identified. Alternatively, I also have some TGs with no close Matches and lots of distant apparent Matches – sort of like a pile up area. This situation leads me to believe the MRCA may be at the fringes of my genealogy or beyond. Maybe adjacent TGs will be able to help…

10. Chromosome Maps/Generation. As I’ve mentioned in several blog posts before – each parent gives us 23 chromosomes and all 3 billion base pairs in a genome. On each side, our two grandparents provided segments that account for the same 3 billion base pairs – through roughly 57 segments that cover all of our Chromosomes. And so it goes for each generation – our Ancestors in each generation provide sufficient segments to fill up all our Chromosomes. With this TG Summary spreadsheet, it’s easy to see the segments from any Ancestor in a generation. For instance my father’s mother’s Ahnentafel is 5 – I can look down column G3 and see which TGs have a 5 and easily note the appropriate Start and End points to get the Mbp for each grandparent segment (or I could resort the spreadsheet on column G3 and just sum the 5s). Repeat for Ahnentafel 4 – the sum of Mbp for 4 plus 5, had better add up to the whole for that side. [arithmetic check!] I could Paint or map those segments which would cover all of my Chromosomes. Do the same thing with Ahnentafels 12 through 15 on my maternal side to map (or Paint) my great grandparent segments.  It all depends on how much of the TG summary I can fill out.

11. Sticky Segments – It’s easy to see “Sticky” segments – a segment of DNA that must have traveled down many generations intact to get to me. See TG 09A24 in Figure 3 below. Yes, this segment probably started out somewhat larger, but the segment I have in my body (TG 09A24) had to persist from Ancestor 354, through 8 generations, to me.

12. Progress – This TG Summary spreadsheet offers a good way to track your progress (if your objectives include linking Ancestors to Segments, or “proving” your Tree with DNA).

13. Focus – In any case, this TG Summary spreadsheet helps me focus on the *Most Distant Common Ancestor* Chromosome Map objective.

Here is part of my TG Summary Spreadsheet only with known MRCAs (bolded  & highlighted) Ahnental numbers :

Figure 1

Next is part of my TG Summary Spreadsheet including “must be” Ancestors. And a few of the known, even numbered (husband) Ahnentafels were changed to odd (wife) Ahnentafels – as appropriate.

Figure 2.

Now, below, I’ve added some double underlines at crossover points:

Figure 3.

NOTES on this Figure 3:

1. Note the 183 to 182 crossover between TG 06O25 and 06Q25. Ancestor 91 had the two segments as maternal and paternal segments and passed them on as a full maternal segment to Ancestor 45, which then must have been a “sticky segment” down to me.

2. Note TGs 08A24 through 08F24 appear to flip-flop from 8 to 9 to 8 to 9. That almost certainly would not happen. And upon examination I see that TG 08D24 should have been changed from 8 to 9 [NB: by convention I use an even Ahnentafel to represent an MRCA couple, which is this case would have been 8 & 9– so the 08D24 8 has an equal chance to be a 9. Given that both adjacent TGs are a 9, the best guess is to make it a 9. Then there is 1 crossover instead of 3.

3. While we are looking at Chromosome 8, it looks like the 9 will crossover to a 10 before 08L25 starts; but the crossover will actually be in G3, and TG ID 08K24 could be either a 4 or a 5 in G3. This would mean one crossover in Chr 8 in Gen 3 – highly probable for Chr 8.

4. Look at TG 09A25 – two things: although it’s 5.5Mbp long, don’t be fooled – most of the Shared DNA Segments in 09A25 are 15cM segments; and only one Match has a distant MRCA at Ahnentafel 354 – this is a fairly iffy, and I would not be surprised if someday I found a closer paternal cousin on this segment – even one on a 2-4 branch (but for now this is the only clue I have for this TG, and I’ll keep it until something better comes along).

5. Look at TGs 07L24 and 07N25 – there is a crossover here at G3, and the two TGs go back in two very different directions (to two very different geographic areas). I generally find that this type of crossover is fairly crisp, and easy to identify. Other TGs with crossovers somewhat more distant seem to have a fuzzy overlap – often the crossover point cannot be readily pinned down. I such cases I just pick a compromise crossover point. As I’ve noted before, our focus should be on the bulk of the TG segment, from an Ancestor, and not be too concerned about a little fuzzy overlap of TGs.


REMEMBER: Your Ancestry is a very unique arrangement of Ancestors – which does not change. Your DNA is a unique tapestry of segments and crossover points – which does not change. Your DNA is linked to your Ancestors in one way – which does not change.

All of our tools help us to determine our Ancestors and segments and how they are interconnected. The Leeds method and Virtual Phasing can help with Generation 3 (G3 above) – the results should be the same as your grandparents and your grandparent segments. DNA Painter can help paint the same segments you see in the TG SUMMARY above – but more colorfully, and perhaps closer to your style of figuring things out. Clustering (in all its various manifestations); Shared Matches (aka In Common With; Relatives in Common, Shared DNA Matches); segment Triangulation (by GEDmatch, MyHeritage, 23andMe, or DoubleMatch Triangulation at FTDNA; or through a Spreadsheet, as I do); and Trees and genealogy Tools primarily at Ancestry – are all good tools that are designed to help find Common Ancestor and DNA segments. Use the tools that work best for you. This TG SUMMARY may also help you.

SUMMARY – NB: This spreadsheet summarizes WORK. It summarizes the segment Triangulation of many DNA Matches – not an easy task, but one when accomplished, remains relatively static. It also summarizes a lot of genealogy WORK determining Common Ancestors with our Matches. As we document our TGs and dig into the genealogy, we begin to build a mountain of evidence linking our Ancestors to our DNA, and vice versa.

[35BE] Segment-ology: TG Summary Spreadsheet by Jim Bartlett 20211222

Ancestor Spreadsheet

The most important spreadsheet for the genetic genealogist, IMO, has nothing to do DNA or segments – it’s an Ancestor Spreadsheet. A simple spreadsheet of Ancestors is a very valuable tool.

This spreadsheet starts off very simple and can expand any way you want. Here are the column headers:

Ahnen – Ahnentafel number (this is a key to sorting and will help you in other ways, too)

L Name – Surname

F Name – Given name(s)

B Date – Birth date (pick a standard format and stick with it)

B yr – Birth year

B Place – Birthplace

B St – Birth state

B Co – Birth country

D Date – Death date

D yr – Death year

D St – Death state

D Co – Death country

D cause – Cause of death

M Date – Marriage date

M yr – Marriage year

M Place – Place of marriage

M St – Marriage state

M Co – Marriage country

I Date – Immigration date

Remarks – Add anything you want

D age – Age at death [D yr minus B yr] [also serves as a Quality check]

M age – Age at marriage [M yr minus B yr] [also serves as a Quality check]

Ch – number of children

Rel – religion

Prof – Profession

Mil – highest level

War – RevWar, 1812, CivWar, etc.

Y-DNA [halplgroup of all male line]

mtDNA [haplogroup of all female line]

FG – Find-a-Grave [I paste in the hyperlink for easy access]

LDS – The FamilySearch ID# for the Ancestor [this may change from time to time]

For the spreadsheet header, just type in the above list (to the left of the hyphen) across the top row.

I started with a Tree at Ancestrycom that was mostly just my Ancestors – Click on Tree search (top right); then select ‘List of all people”; then highlight that list and paste it into a spreadsheet. There is still some amount of manipulation, but I had a good base to start. Or you could just type the spreadsheet from scratch. Or perhaps manipulation from a GEDcom or other Tree software.

Here are some benefits and things to do with this Ancestor Spreadsheet:

1. First – this is your personal spreadsheet – modify it any way you want – you can delete any columns you don’t want and/or add any new columns for data you want. You can hide any column(s), so that only the information you tend to use all the time is shown (you can unhide at any time).

2. This is a very handy inventory of your Ancestors – a printout will only be a few pages.

3. This is an easy repository of key data elements of your Ancestors

4. This is my go-to lookup table for Ahnentafel numbers

5. A searchable database

6. A variety of spreadsheet sorts:

                A. Ahnentafel sort – groups husband and wife together and by generation

                B. Surname + B yr – groups surname lines in chron order => surname lineage

                C. B St – groups Ancestors by states; sort on “B county”, if you add that column.

7. I include Potential Ancestors, but highlight them as Potential.

8. I include “Alternate” Ancestors (also highlighted), when there is an unresolved alternative.

9. Blank spaces can highlight data you don’t have – they are a good tickler for what you need to research. Periodically, I’ll select one to tackle.

10. Add an additional row for each generation – this is a “separator” between generations; Example of the text in a Generation row:  32 GEN 6; 3xG grandparents; 4th cousin Matches [where the 32 is in the Ahnen column.

11. I select a some columns that will fit on one page, and hide the rest, and print out about 4 pages (the top Ancestors) which I always have handy – particularly while traveling.  I refer to this spreadsheet literally every day – so, IMO, it’s worth the work it takes to prepare it.

12. Please post any additional uses you find for this Ancestor Spreadsheet.

Here is an example of part of my Ancestor Spreadsheet:

Figure 1:


1. This is just a sample; some columns have been hidden or reduced in width to get a lot in the picture.

2. This Ancestor Spreadsheet is not intended to replace my on-line Tree(s) which are full of documentation. This has key data, and an Ahnentafel place holder for every Ancestor. Ancestors in my Tree more than once are in this spreadsheet more than once – it helps to understand Pedigree collapse.

[35BA] Segment-ology: Ancestor Spreadsheet by Jim Bartlett 20211222 [Edited 20211223]

Segmentology Common Ancestor Spreadsheet

I’m going to try a format here that will make it easier for me to explain some of my spreadsheet tools, and give you an easy way to copy the header (you can adjust the column widths to suit your self). Please let me know if this works for you, and I’ll try some more of them.

Copy the above column titled “Header Row” and paste it into your spreadsheet using the Transpose option. It should create the Header Row for the Common Ancestor Spreadsheet.  [Edit: it appears this doesn’t work from the image above – so just type them in a row across a spreadsheet.]

There are several types of rows for you to input:

1. Include one row for each of your Ancestor Couples – I highlight these rows      

2. There is one row for each Match with each known Common Ancestor (MRCA);              

3. I add a row for my MRCA Child & birth year with a NOTE to refer to appropriate Ahnentafel for more  

4. I add a row for Ancestor multiple marriages, and put marriage year in born column      

                This separates full cousins and half cousins.

5. If something looks fishy, or needs more investigation, I highlight it in orange/mud color.             

6. If an Ancestor/Ahnentafel number and a TG are in conflict, I highlight it in red. The genealogy may be correct but the shared DNA segment did not come from the MRCA         

Other NOTES:   

1. The main sort for this spreadsheet is Ahnen + born+ born +born columns         

                NB: Highlight all columns before sorting.

2. Another sort is on Match Name to analyze multiple MRCAs – only one TG per MRCA    

3. If you want to compare spreadsheets for different Test Takers, be sure to fill in the TT column first. Combine spreadsheets, sort, analyze, then sort on TT and separate the spreadsheets.       

4. Sidebar: I have an Ancestor Spreadsheet – one row for each Ancestor info, including the Ahnentafel number!  

5. I have typed all the data into my Common Ancestor spreadsheet – a lot of work             

                Idea: If you have a download of AncestryDNA Matches, start with that data for ThruLines Matches

6. If you want to be able to sort this by side (your paternal and maternal sides); add a column for P or M (or 2 or 3)               

7. Do not hesitate to add any other columns (or rows) that may be useful to you. I made up this spreadsheet, feel free to change it as you like.


1. It captures all of your Matches with Common Ancestors [some may be gone tomorrow…]        

2. It arranges the Matches’ descendants from the MRCA like a Family Group Sheet           

                Easy to compare with your own research

                Helpful in spotting many errors

                Easy to see Matches who are relatively close cousins to each other – good conversation starter

                Easy to highlight real and/or potential errors

                Easy to spot a Match at two companies with different names

3. Shows TG threads in a family [maybe Clusters too, haven’t tried them yet)       

                Makes it easy to spot TG threads through a family (closer Ancestors will have more TG threads)

Here is an example from my CA Spreadsheet:

[35BC] Segmentology Common Ancestor Spreadsheet by Jim Bartlett 20211219  

Using MyHertiage Labels for Triangulation

My Heritage just released an improvement to their “labels for DNA Matches”. See their blogpost at:

These are intended to help you organize your DNA Matches into groups. And, AND, AND … you can “Export entire DNA Match list” (click on the 3 vertical dots to the right of Filters and Sort by), and this spreadsheet will include a list of any labels associated with each Match.

This is a huge time saver for Triangulation. To the extent that we can identify our Matches as Paternal and Maternal, the Triangulation process becomes very simplified. Paternal side Matches will only Triangulate with other Paternal side Matches. NB: watch out for any Matches that may relate to you on both sides. For the vast bulk of our Matches, however, all we have to do is sort by side + Chr + Start and form groups.

If you’ve already done a lot of Triangulation, this will provide a good Quality Control check.

There are a few pesky details: you have to assign the dot labels*…; you have to merge the Match list with the segment list…; you have to analyze the start/stop locations and make a judgment call as to where the Triangulated Group starts and ends.  But aside from these chores, the main headache of checking for Triangulation is gone. Having the effect of “phased data” means the shared segments on one side have to Triangulate only with other segments on that same side.  *Clustering and Shared Matches will often indicate that we can assign “side” labels on a group basis. Triangulated Icons should always indicate the same “side”.  

[10D] Segment-ology: Using My Heritage Labels by Jim Bartlett 20211215

Distribution of Cousins

This blogpost is overtaken by a better analysis by Kurt Allan, based on other analysis by Louis Kessler and information from Doug Speed that his chart was intended for a different purpose and might not apply to genetic genealogy. The result is a spreadsheet similar to the one below, but with a more normal distribution curve with 7C-9C occupying the mean. This is very good news for genetic genealogists – most of our Matches are well within a genealogy horizon. I hope to be able to post or link to Kurt’s final graphs soon.

A recent discussion on the Genetic Genealogy Tips & Techniques facebook page asked about what percent of our DNA matches we should expect at various genetic distances. I’ve often wondered about this too. As I thought about it, we should be able to apply the “Speed and Balding” analysis to this question. The S&B graph shows the probability of a matching DNA segment at different generations (think cousins), for given ranges of shared DNA. See the graph at the ISOGG wiki here.

I scaled each “bucket” in this chart as best I could and put the bucket percentages in an excel spreadsheet – see below.  In the Speed and Balding chart, cM ranges are along the x-axis; percentages on the y-axis; and the “generations” are shown as stacked bars (or “buckets”) for each cM range. The numbers in the body of this chart are the percentage for the cM range and Generation.

I had in my files a complete download of my AncestryDNA Matches by DNAGedcom Client from several years ago, before the Ancestry purge of 6-7cM Matches. I had 131,824 Matches and it was easy to sort by cM and determine the total number of Matches for each column (cM range) in the S&B chart.  Finally I applied the S&B percentages to my breakdown of Matches to get the following  chart.

I know it’s a “squinter”, but I wanted to show the whole spreadsheet. Here are explanations of the lettered rows:

A.            The cousinship which corresponds to the S&B generations back

B.            Speed & Balding generations

C-N.       The first column is cM range groups that correspond to the S&B chart.

C-N.       The second column is the number of my Matches in each category –131,824 Total.

C-N.       The next columns: multiply S&B percent by number of Matches in the cM range

P             Total number of Matches for each cousinship

Q             Percent of cousins vs the 131,824 Total

Key points

1. I could be off by a percent or two in my scaling of a printout of the Speed and Balding chart – but the totals are pretty close, and what I am really looking for is trends and order of magnitude.

2. Line Q, percent of total, was a lot flatter than I had expected – less than 4 percent for any cousinship. I had expected something closer to a normal distribution curve – even a long one, but with a “hump” somewhere. This indicates the two competing factors: an increasing number of cousins with each generation going back, verses a decreasing probability of a shared DNA match (above 6cM) with each generation going back.

3. There are a lot of Match-cousins to work with. Although only about half of all our Matches would be related to us out to the 19th cousin level; nevertheless, there are thousands of cousins in every cousin “bucket”.

4. In my own case I need to use judgment and temper some of these results. Both of my parents were only children, so I have no 1st Cousins. And my great grandparents did not have large families, so I also don’t have many 2C. However, I do have about 300 3C Matches and 600 4C Matches identified, so far, and there are plenty more out there (at least per Speed and Balding). And I am finding many 5C-8C Matches (but my known Tree begins to thin out after that.)

My Takeaways

1. Autosomal DNA “works” throughout a genealogy horizon for most of us.

2. The limiting factor is NOT the atDNA, it’s the genealogy – the lack of good Trees among our Matches; and the shrinking body of documentation the farther back we go.

3. When Matches Triangulate or group in Clusters, it’s often worth the effort to extend their Trees and find the Common Ancestor.

This blog post is one in a series to try and outline what you can generally expect – to put some generalized boundaries on genetic genealogy.

Anyone is welcome to use my estimate of the S&B data in the first spreadsheet, and apply it to the distribution of your own Matches. Please let me know if you see a glaring error in this process or the results.

[06D] Segment-ology: Distribution of Cousins by Jim Bartlett 20211209

Genetic Genealogy Spreadsheets

Spreadsheets are an important tool in Genetic Genealogy. Here are some of mine…

ANCESTORS – Names, dates, locations, and Ahnentafel # are the key foundational data in this spreadsheet. Over time I’ve added columns for: Immigration year; age at death, age at marriage, number of children, Religion, Profession, Military, War, Y-haplogroup, mt-haplogroup, Find-A-Grave hyperlink, remarks. Add any other column of interest to you – you just need to fill it in… I add in Potential (or Alternate) Ancestors (highlighted) to keep track of those possibilities.  I have a “dup” column to indicate which Ancestors are duplicates. This is a very handy reference for me. Two main sorts – 1) by Ahnentafel #; and 2)by surname & birth date. [Initially I took a GEDcom of an Ancestors only Tree and put it into a spreadsheet – then massaged the columns]

COMMON ANCESTOR MATCHES – Names of all Matches who have a Common Ancestor(s) with me. Key data: Name, Admin, cM, #Segs, Company, CA Ahnentafel #, Cousinship, columns for name and birth year of child, grandchild and great grandchild of CA (for Match’s line of descent); hyperlink to Tree. I also have columns for TG or Cluster, GEDmatch #; Remarks. I also have columns to indicate (to me) if I’ve filled in the Notes box of the Match, entered the line of descent to the Match in my Tree… Main sort is by Ahnentafel # and dates of Child, Grchild – this sort looks like a Family Group Sheet – and is very helpful in tracking TGs and Clusters. It also lets me focus on family groups which often group together in TGs or Clusters.

TG MASTER – Match name, company, Admin, email, Segment info (Chr, Start, End, cM, SNPs), TG ID, Side (M or P), CA info (Ahnentafel #, Surnames of Couple, Cousinship, Tree hyperlink); GEDmatch #; date. If you plan this type of spreadsheet for other people, add a column for initials of test taker (you can then, briefly, combine spreadsheets, do analyses, then separate them again – one spreadsheet per person). Advanced: I have columns for each of 10 generations, and enter my Ahnentafel #s from my parent (2 or 3) out to the CA – this helps me analyze multiple CAs in a TG. Headers: 46 Chromosome bars (rows to separate data); TG bars (that summarize the Chr, Start and End of each TG and the CA) – sometimes there are multiple bars – I highlight the most likely. Main sort: by Side, Chr, Start (this will arrange all Shared Segments into their respective TGs – which should have one Ancestral line)

TG SUMMARY – Chr, Start, End, TGID, Side, columns for 8 generation of Ahnentafel #; Cousinship, CA Surnames; NO Matches. This is a summary subset of the TG MASTER – except I fill in only the Ahnentafel # for known CAs out to most likely distant CA. In italics, add in Ahnentafel #s from Cluster analysis compared to known TGs – this often extends the evidence in the TG (this is an experimental spreadsheet at this point. Sort: Side, Chr, Start .For me, this is a handy 2-page crib sheet.

WALK THE CLUSTERS BACK – a fairly technical tool. Start with a download of Excel data for Clusters based on a 50cM threshold (from DNAGEDcom Client). This will include Match name, cM and any Notes you’ve entered for each Match – this Note info is very valuable to have in this WTCB spreadsheet. Add columns for Ahnen (or CA Surnames) and a TG or Cluster (CL) code and Remarks. Finally add a column for serial # of each row (1 to how many rows you have at that threshold – so after a sort, you can reconstruct the original Cluster groups – just type a 1 at the top and drag it down in a series) – call this column CL50. And add another column – called CL# – and add in the Cluster # for each Match (I wish DGC would include this in the download spreadsheet. Then the work is to determine the Ahnentafal/CA and/or TG CL ID for as many Clusters as possible (hopefully your Notes will show you all the info you’ve collected about each Match). Add a summary row for each Cluster (using 0.4 in the serial number column – now when you sort on CL# and CL50, all the Clusters will be grouped with a header. IF there appears to be a consensus for the Ahnentafel/Surname and/or the TG/CL columns, enter that in this header row. Next, rerun the Cluster report with 45cM threshold – add two new columns for serial # in a new CL45 column and the Cluster # in the new CL# column. As before, add in a header row for each Cluster with 0.4 in the CL45 column and the Cluster # in the CL# column. Now add this spreadsheet to the CL50 spreadsheet, sort on Match name, and combine duplicate Matches onto one row (Matches in both CL50 and CL45 runs will have two Cluster #s and two serial #s – don’t worry. Resort on CL# and CL45 to get all the Matches in Cluster order again, with the added info from CL 50. Again, analyze each Cluster with a goal of finding the CA and/or TG/CL for most Clusters (for the Cluster header rows. If advantageous to see where a new Cluster is going, make a duplicate copy of Match rows which have strong affinity for other Clusters (and code it with the other Cluster number) – use to help identify CA for new Clusters. This is very much a judgment call, which will be confirmed or refuted in follow-on Cluster runs. Drop the cM threshold by 5cM and repeat. The number of Matches begins to increase dramatically – it’s a lot of work. But the benefit is that you are imputing Ancestral lines to many Matches who are Private or have little/no Tree. If you add the imputed into to the Notes of these Matches, they will show up in Shared Match lists and “flavor” them with an Ancestral line. Again – this process is experimental and requires us to use judgment. Future investigation – the Clusters from different companies should be roughly the same – it would be great to be able to link Ancestry Clusters (with many MRCAs) with Clusters from 23andMe, FTDNA, MyHeritage and GEDmatch (with TGs)…

Apologies – this WTCB “short” summary got a lot longer than I originally intended. I’ll have to post a more complete version later. The takeaway is: gradually reduce the cM threshold of Cluster runs and trace the Ancestry from the initial grandparents on out the ancestral lines, using new, smaller Matches which are often more distant cousins with more distant MRCAs. Think of a time-lapse movie of a plant growing, with new limbs branching out over time. If (when) we see a Match with an MRCA which is clearly out of whack with the “history” of the Cluster, it’s time to see if that Match would better be relocated to a different Cluster (per the gray cells) or a different MRCA needs to be found. It is OK to move a Match to a more probable Cluster if it has a lot of Shared Matches with that Cluster, too. We can use our judgment…

[35B] Segment-ology: Genetic Genealogy Spreadsheets; by Jim Bartlett 20211207

Distribution of TGs Part 4 (Spreadsheet)

Common Ancestor Spreadsheet

By popular demand, here is a portion of my Common Ancestor Spreadsheet:

I’ve added letters at the top of each column for ease in describing them:

A – Initials for the testing company – if a Match tests at multiple companies, I list them for each one.

B – This indicates if the Match also has a ThruLines (TL) or UnListed Tree (ULT) or Theory of Family Relativity (ToFR), etc. Perhaps a quirk of mine in data collection, but this lets me sort the spreadsheet to select all the TLs, for instance, and compare with the AncestryDNA TL list for completeness.

C. The name of the Match – may also include the Admin or Point of Contact

D. Total cMs

E. Number of Segments

F. Ahnentafel number for the MRCA

G. Cousinship

H. A code for Headers (C is a Green separation for each generation; H are my Ancestor Couples; Hch are my Ancestors who are a child of the Ancestor couple – also highlighted in yellow; Also Hm is a row for a 2nd marriage of an Ancestor – usually with a note that Matches who descend from subsequent children would be half-cousins (use the marriage year in the K column)

I. Ancestor Couple

J. Children of Ancestors – these are the children the Matches descend from – daughters are noted with the surname they married (important to identify grandchildren, etc.) Each Ahnentafel should have a row for my Ancestor (and birth year).

K. Birth year of children

L – O – like J and K

P. This is just one column to add the rest of the descendants down to the Match, if you want to do that (I’ve deleted my entries here as it gets too close to living people)

Q. Triangulated Group IDs – I add a “c” when the TG is implied from a Cluster or consensus among Shared Matches.

R. Add any notes you want – some of mine includes notes when a Y-DNA or mtDNA (testing) path is in the line of descent; or if the line of descent is “iffy”, IMO; or TL was wrong, and this is the fixed/correct version; etc. (whatever you want)

S. Tree URL – this is often very handy to review and/or to quick get back to the Match.

I cannot emphasize enough that spreadsheets are very personal, and you should exercise your own judgment to adopt this one to your own preferences, and to add any other columns you want (realizing that each additional column is more work to maintain).

Here are some additional columns from my spreadsheet which I occasionally use:

Hg – Haplogroup (Y or mt) if it applies to the Match and is important to me

Gm – GEDmatch ID# for the Match

Related – I often note when two (or more) Matches are closely related to each other (this cautions me to “dilute” the value of, say, two children or siblings, as they do not add to any consensus.

MyT – I note in this column (y) if I’ve added this line of descent to my main Tree at Ancestry – it helps me get more ThruLines…

Other – I note in this column any other MRCA Ahnentafel this Match is related to me on – the Match is in my spreadsheet for each such additional relationship (it remains a task to figure out which MRCA goes with the Shared DNA Segment).

Email – email of the Match

The main purposes (for me) of this Common Ancestor Spreadsheet include:

1. Document (in one handy place) all of my Matches with MRCA

2. Use the Family Group Sheet format to check the accuracy of Match descendants against my own Family Group Sheets and/or genealogy research.

3. Determine closely related Matches (this sometimes results in a good communication thread that shares info, draws in other research. and maybe more interest in DNA testing.)

4. Tracking the TGs vs MRCA; particularly with respect to the “Rules”.

Feel free to post a comment about any additional use you see for this spreadsheet; and/or any improvements or drawbacks…

[15K] Segment-ology: Distribution of TGs – Part 4 by Jim Bartlett 20211013

Distribution of TGs – Part 3

This Part 3 will look at conclusions (what can we learn from all of this), and propose new spreadsheets to track all of your TGs or track TGs/Clusters through other children of our Ancestors (what we can do!).

Before I review the “Rules”, I want to focus set the stage on the Big Picture: Our autosomal DNA consists of 22 Chromosomes from each of our parents. And each of these Chromosomes has a mosaic of segments from our Ancestors. One analogy is an archeological dig with layers of artifacts – the deeper we go, the more distant (further back in time) the artifacts. Our DNA has a similar pattern. Each of our Chromosomes is composed of segments from our grandparents, passed to us from a parent. Going back another generation, each of our Chromosomes is composed of segments from our Great grandparents; and so on. Even if we went back 100 generations, we’d find that our Chromosomes were made up (completely) with DNA from that generation. This is not to say that every Ancestor in a generation contributed to our DNA; it is to say that some of the Ancestors in a generation contributed all of our DNA. And all of the crossover points are there if we can dig deep enough. But our DNA does not include “signposts” or markers that identify crossover points. Segment Triangulation is the only method I know to determine these crossover points and define specific segments from Ancestors (beyond Visual Phasing of grandparent crossovers). One drawback of Triangulated Groups (TGs), is that they are formed from available Shared Segments with Matches, and they are not formed at any particular generational level. However, we do know that each segment of our DNA came from an Ancestor – each segment represented by a TG came from an Ancestor. When we find a number of (widely separated) Matches in a TG agree on the MRCA, this is powerful evidence that the TG-segment came from that Ancestor. We can then map these TGs and MRCAs. In this respect, we learn that segment Triangulation (TGs) is essential to confirming our biological ancestry. We learn that the DNA is not scattered willy-nilly over our DNA. There are genetic guidelines – which I call “Rules” in this blogpost series. Our Chromosome Map should be in general agreement with these rules. And, perhaps in Part 4, I’ll try to outline how we can use these rules to predict much more.

So what do we learn/do with all this musing?

1. Learn: We can understand how TG segments originate in Ancestors – maybe 5 to 8 generations back – and pass them down to us, and our Matches. At each generation – coming down/getting closer to us – our Ancestors have more TGs – until our parents each pass down about 150-200 TGs to us.

2. Do: Use spreadsheets to track and analyze this growing amount of data… Examine closely areas that deviate from the rules.


Here is a summary of our “Rules”.

-Rule #1: We can expect roughly the calculated numbers of TGs from each generation – an order of magnitude [See Table in Part 1]

-Rule #2: We can expect about 34 crossovers to occur per generation on each side.

-Rule #3: Shared DNA (with Matches) reduces by roughly 1/4 with each generation.

-Rule #4: We should not see Matches beyond 3C, with the same TG, descending from more than two children of a CA.

-Rule #5: The amount of DNA, and number of segments, in each generation, are not affected by external factors. [The number of TGs may be affected by the Matches you have.]

-Rule #6:  The sum of the DNA contributions of all Ancestors at each generation will be 100%. This is a hard rule that is true at every generation.

-Rule #7:  Each of our Ancestors will have all of the TG-segments both their parents had.

-Rule #8:  A TG that subdivides going back, separates into a two smaller segments – one from each parent.

Observation: Based on my 372 TGs, I estimate, using an 8cM threshold, most of you should get 150 to 200 TGs per side. They will range from small to large and span almost all of your DNA (there may be a few gaps – it all depends on the “coverage” provided by the shared DNA segments with your Matches.)


I think we should track and analyze our TGs. My preferred method is with spreadsheets:

1. Master atDNA Spreadsheet – this is an “everything but the kitchen sink” spreadsheet for me. I include every IBD segment (over 7cM) of every Match – with segment, genealogy, and other information. I still plan, someday, blogposts about spreadsheets. This is a cursory overview. A spreadsheet is highly personal – I recommend you start with downloads from your testing company and add columns to suit yourself – mine is continually evolving.

Here are some of the columns in my spreadsheet:

        a. Match info: full name, last name, company “name”, email, POC, company, Notes

        b. Segment info: Chr, Start, End, cM, SNPs [from the companies} and TG ID (from me)

        c. Genealogy info: Tree URL hyperlink; cousinship (e.g. 3C1R); MRCA couple surnames, side

        d. Other info: GEDmatch ID, dates of communication, etc., etc.

        e. Most of this info is from company downloads, the rest is typed in as I get it.

My spreadsheet has over 20,000 rows… including the following “Header” rows

        f. 22 paternal and 23 maternal Chromosomes – Header/dividers

        g. TG summary Header/dividers – uses earliest start location of TG; MRCA (per my judgment)

        h. Alternate TG Header – to records alternate MRCAs for some TGs

Spreadsheet sorts – each of these sorts is a valuable tool for me

        i. Alphabetical by name

        j. Chr & Start – used to Triangulate segments (as they are added)

        k. Side & Chr & Start – clearly groups all Matches in a TG – should have same MRCA

        l. TG summary Headers, only, by Side & Chr & Start – to analyze MRCAs by generation [these headers have Ahnentafel numbers (in columns for each generation) to the MRCA].

        m. This TG summary sort also allows an analysis with respect to Rules #1, #2 and #3 by generation.

2. Common Ancestors Spreadsheet – this is a list of all Matches with Common Ancestors with me (now about 6,000 rows)

        a. Match name, shared cM, cousinship, Tree URL; name/birth of MRCA descendants; Ahnentafel

        b Any known TG ID or Cluster

        c. A header row for each of my Ancestors (usually a couple)

This started with columns for Children of Ancestors; their birth year; and same for grandchildren – this info was typed in for each Match’s line of descent from the MRCA. I have since expanded it to include columns for remaining line of descent (and birth, down to the Match. For females I add married name; for example: Nancy m FLEMING to indicate succeeding descendants have a different surname (saves a little time and space).

Most of this info was from AncestryDNA ThruLines, but I have a number of rows for Matches from the other companies (and the TG info for them, which is like gold).

When this spreadsheet is sorted by MRCA Ahnentafel & Child birth, it looks like a series of Family Group Sheets for each MRCA family.

        d. This makes it very easy to check against my Family Groups Sheets researched and developed over the past 45 years. I highlight conflicts in a mud color for further research and analysis. 

        e. This spreadsheet also has a column for for Potential Ancestors [POT ANC] (usually from Ancestry or MyHeritage]

        f. For each Family Group, it’s also easy to check the range and average of Shared cMs for that family

        g. Maybe most importantly for me, it allows me to see if there is a TG and/or Cluster thread in each family

        h. I can also check for violations of Rule #4. This has already highlighted a few such violations – almost all of which led to an alternate MRCA with a much better “fit”.

        i. All instances of a Match with multiple TGs and/or multiple MRCAs, must be adjudicated. A TG can only link with one ancestral line. This spreadsheet is a good tool for that analysis.

With this Common Ancestors spreadsheet  I’m finding three things: a) each Ancestor does tend to have a consensus of Clusters and/or TGs; and there is the occasional outlier (this illustrates that just because you have shared DNA and an MRCA with a Match, it doesn’t necessarily mean the shared DNA came from *that* MRCA – there could be other MRCAs); b) there tends to be only a few groups (Clusters and/or TGs) in each Family Group – roughly in line with the table at the beginning of this blog post; and an occasional outlier of more than 2 children with the same TG (which indicates to me there is probably an issue – probably, also, where the shared DNA didn’t come from *that* MRCA).

3. TG Summary Quick Sheet – taken from my Master atDNA Spreadsheet, this just has a few columns, and I can fit all 372 TGs into 2 pages (maternal and paternal).

        a. Columns: Chr; Start; End; TG ID; side; 8 columns for 8 generations of Ahnentafel numbers; MRCA Ahnentafel; MRCA cousinship; MRCA surnames

This Quick Sheet (1-page; front/back) is a handy reference – linking TGs to MRCAs and finding TG IDs for any segment. I include the Chr Headers (solid black) which highlight the TGs in each Chromosome.

I cannot over emphasize that spreadsheets are a tool, and you should adopt any spreadsheet to your own objectives and methodology. Don’t be afraid to add or delete columns or header rows.

Final thoughts for this Part 3 – think through the guidelines (“Rules”); and set up spreadsheets to help track and analyze your data. However, building and maintaining a spreadsheet to manage your Matches and Segments or Common Ancestors takes time – it’s not for everyone. Or… use whatever system you want – genetic genealogy is your hobby, and you are free to enjoy it however you want.

I might have a Part 4 with some more thoughts …

[15J] Segment-ology: Distribution of TGs – Part 3 by Jim Bartlett 20211008

Distribution of TGs – Part 2

Part 1 of this topic covered some of the background of how TGs are distributed over our Ancestors. This post is about where Triangulate Groups (TGs) are formed and their journey from the Common Ancestors (CAs) down to us and our Matches.

Recap of Part 1:

-Rule #1: We can expect roughly the calculated numbers of TGs from each generation – an order of magnitude

-Rule #2: We can expect about 34 crossovers to occur per generation on each side.

-Rule #3: Shared DNA (with Matches) reduces by roughly 1/4 with each generation.

-Rule #4: We should not see Matches (over 3C), with the same TG, descending from more than two children of a CA

-Rule #5: The amount of DNA, and number of TGs, are not affected by external factors.

-I have 372 TGs, roughly 186 per side, which is close to the 193 TGs predicted to come from my 16 4xG Grandparent couples (6 generations back – 5C level) on one side – about 12 TGs per couple. [See the table in Part 1]

The musing continues…

The TGs we eventually get were in our Ancestors’ DNA somewhere.

Think about the Ancestor who first formed (through recombination) the DNA segment that finally came to you as a TG segment. That Ancestor passed a whole set of Chromosomes to the child who was also your Ancestor – and that TG segment was included somewhere in all those Chromosomes. In these distant Ancestors the TG segment was probably part of a somewhat larger segment. With each succeeding generation that larger segment was either subdivided by a recombination crossover or passed along intact. The smaller the larger segment got, the less likely it was to be subdivided. Near the end of its journey, the TG segment was passed from a parent down to you.

Which Ancestor forms a TG?

Which Ancestor first formed the TG? The most distant cousins, who share the full TG segment, determine the Ancestor. If four 5C all share almost all of the TG segment, then that segment probably came from a 4xG grandparent. NB: 6C and 7C can also be in this TG (usually sharing only a part of the TG segment); and 3C and 4C can also be in this TG (but they aren’t the most distant); and 1C and 2C may actually share this TG and an adjacent TG. It’s often hard to get enough good cousins in a TG to nail it down with certainty.

All TGs from an Ancestor, come through one* child to you.

If an Ancestor couple is “responsible” for 12 TGs, all 12 of those TGs must come down through the one* child (usually) who is our Ancestor. The DNA is also coming from our Ancestor couple down through other children of the Ancestor couple and then down to our DNA Matches.

[*It is possible that we descend from two (or more) children of an Ancestor. If so, each one is treated independently. If an Ancestor at this level was passing down an average of 12 TGs (see the table in Part 1), then that Ancestor would need to pass down roughly 12 TGs to each child who was our Ancestor. Siblings share some DNA with each other. So, some of the TGs could be shared, some would be different. A single child is used to illustrate the concepts in this blogpost.]

All TGs from an Ancestor (MRCA), come through other children to our Matches.

Take an Ancestor couple with two children – all TGs pass down through the one child who is our Ancestor to us; the same TGs also pass down through the other child to our DNA Match-cousins. If an Ancestor has three children, again all TGs pass down to us through the one child who is our Ancestor, and those same TGs could be split between the other two children. If an Ancestor has multiple children, the TGs could be distributed over those other children with two concepts at work: 1) not every child has to get and pass on a TG; 2) The same TG cannot be passed down through more than 2 different children (Rule #4). [An Ancestor couple with only one child is trivial – all TGs pass down through the one child to us, and we have no Match-cousins from this Ancestor].

Amount of DNA vs Number of Matches

It appears to me that roughly the same amount of DNA (TGs) should come from our Ancestors in a large family as from a small family (review Rule #5). Each Ancestor has the same chance of passing DNA down to us as another of our Ancestors (and all of that DNA must come to us through just one of their children – usually). The amount of DNA (and number of eventual TGs) would not depend on the number of children that Ancestor had. But the number of Match-cousins we get would be influenced by the number of other children, and subsequent descendants, they had (and other Rule #5 factors). You might get the sense that I’m trying to emphasize this point – maybe because it’s hard for me to realize that I get the same amount of DNA (in TGs) from an Ancestor couple with few children as I do from one of my Ancestor couples with very large families.

Over the past 45 years I’ve determined over 20,000 descendants of my BARTLETT Patriarch – they were farmers with large families. I do find many Matches with MRCAs, but they all seem to be on repeating TGs (or Clusters). With this paragraph, I now understand why. Each of our 64 4xG grandparents (on both sides) will pass down to us an average of 1/64th of our DNA. Experience and random DNA shows this is not exact, but it is a good order of magnitude – each 4xG grandparent will have a little more or a little less than 1/64. However, the sum of all 64 4xG grandparent contributions to our DNA will total exactly 100%. This leads to Rule #6:

6. The sum of the DNA contributions of all Ancestors at each generation will be 100%. You can take this one to the bank. At each generation, all of our Chromosomes will be filled with DNA from the Ancestors in that generation.  I wanted to say our Chromosomes will be filled with TGs from the Ancestors in one generation, but that would not be technically correct. Some of that DNA may be small segments that would not form a TG. But in a closer generation those small areas are recombined into larger TGs. Clearly, from a parent’s generation we get full chromosomes – no small segments…

TGs “accumulate” in closer Ancestors

Let’s assume my 4xG grandparent couple passed down 12 different TGs – to me and our some of my 5Cs.  Because the 5Cs have those TGs, we know the TGs existed in a 4XG grandparent. All 12 of these TGs were passed down through the child that was my Ancestor, as discussed above. That child married a child of another 4xG grandparent couple who also passed down about 12 different TGs to their child who was my Ancestor. This means that this 3xG grandparent couple must have 24 different TGs to pass down through one of their children (my Ancestor). Remember this 3xG grandparent couple will pass down a lot of DNA to their child (46 Chromosomes) – that DNA will include at least those 24 TG-segments. At each generation, the die is cast, so to speak! These 24 different TGs must be passed down through their one child who is my Ancestor (in my line of descent), and on down me. After all, I have each of these 24 TGs. These 24 TGs are part of my “inventory” of 372 TGs that my parents passed to me in my Chromosomes. This reinforces the point that each TG is a segment of DNA that is passed from an Ancestor down to me; and each closer generation has to have all of the DNA (TGs) that their Ancestors passed down to me. This is also the reason a close cousin may well share a single DNA segment that spans more than one TG. As well-known examples: each parent passes down to us a full set of chromosomes that are full of TG segments; each grandparent passes down few, but generally large, segments which are also full of TGs. This leads to Rule #7:

7. Each Ancestor will have all of the TG-segments their parents had.


To backtrack a little, think about a DNA segment that a 4xG grandparent Ancestor passed down that was a recombination of segments from his/her two parents. Analysis depends on which generation we are looking at. A 6C (one generation back, on one of the two 5xG grandparents) would only see one segment or the other in an eventual TG. The same for a 5C, who would only be related through a segment on one chromosome (side) or the other (unless the 4xG grandparent created the same crossover in the DNA he/she passed to another child – a very low probability). A 4C (on the 3xG grandparent child of the 4xG grandparent couple), would see the recombined segment as a “regular” segment (on one chromosome), which could be passed down to two children and wind up as a TG.  This is another reason why some TGs look like they split going back. This leads to Rule #8.

8. A TG that subdivides going back, separates into a two smaller segments – one from each parent.

To summarize this musing: clear back to my 8xG grandparents (and probably more distant), DNA segments are formed which are passed down to a child who is my Ancestor (as well as to other children who are the Ancestors of my Matches). It’s hard to pinpoint the exact Ancestor who first formed the DNA segment represented by my unique TGs. But from that point on down to me, that unique TG must be in that Ancestor, in the child, and in every other descendant down to me. Now, this child marries another of my Ancestors in that generation who is carrying the DNA with other TGs. So, this couple (in that next generation down) has roughly twice the number of DNA segments (that that will form into TGs) to pass to the next generation. Repeat generation after generation. Finally, my two paternal grandparents will pass roughly 193 segments to my father. To be sure, they only pass 57 segments to my father, but those 57 relatively large segments, will include all 193 segments that wind up in my TGs.

We got the TG segment from an Ancestor; each Match got an overlapping segment.

NB: When I say TG-segments pass down from Ancestors to us and our Matches – let me be clear. The TG represents a real, phased, segment of our own DNA.  The shared DNA segments that make up the TG are an overlapping part of our DNA that our Match also has. Each Match may have a different overlapping segment with us. The DNA the Match got from our Common Ancestor may be larger or smaller than the TG-segment we got.

Part 3 will look at conclusions (what can we learn from all of this), and propose a two new spreadsheets to track TGs (what we can do!).

[15I] Segment-ology: Distribution of TGs – Part 2 by Jim Bartlett 20211005

Distribution of TGs – Part 1

This post is about the distribution of our DNA segments (as represented by TGs) among our Ancestors. It’s gotten long and convoluted, so I am going to post it in pieces. This is Part 1.

I currently have over 110,000 DNA Matches – they are mostly spread over 3/4 of my Ancestry from Colonial America – mostly Virginia. [1/4 of my Ancestry is from my maternal grandmother whose parents were immigrants in the 1860s – and I get relatively few DNA Matches on these Ancestors]. So I am thinking about the distribution of say 90,000 Matches over three of my grandparents from Colonial Virginia, and the chore of finding Common Ancestors (CAs) linked to DNA segments – represented by Triangulated Groups (TGs). I’m musing about the Big Picture – the distribution of TGs in our Ancestry. From a macro view can we learn something? Can we predict something?

These Matches represent a lot of different DNA segments passing down to me (and to my Matches) from my Ancestors. However, I do know something about these “different DNA segments” – I have 372 TGs – each one representing a segment of my DNA from one parent or the other. These 372 TGs are the equivalent to phased data, that “cover” all of my DNA – they are arranged, adjacent to each other, from one end of each chromosome to the other. That’s an average of 186 TG segments on one side.

When I look back at my blog post that used simple math to estimate the number of DNA segments we typically get at each generation – on one side – it shows:

Ancestry used to provide Circles back to the 8C level… They currently limit ThruLines to the 6C level, but at one point clearly acknowledged that the shared DNA segments could come from at least the 8C level, and the Circles they presented showed that plenty of folks had Trees with CAs at that level. I have a lot of evidence that indicates atDNA “works” back to at least the 8C level.

At this point in my musing, I’d like to reflect on several “rules”, or guidelines, or pretty valid assumptions about autosomal DNA.

1. Although atDNA is random, the larger the sample size, the closer to the calculated averages we tend to come. This means that we may find some instances of outliers, but with enough data, it averages out. We see this in several instances – a sibling may share a large part of one chromosome with us, but, on average, the total share will be closer to 50% – some chromosomes may be passed to us from a grandparent intact (no grandparent crossover points), but, on average, the total grandparent crossovers will be closer to the reported averages.

2. Science indicates about 34 crossovers occur per generation on each side. In other words, the biology says our DNA is not pureed into mush and then passed down to the next generation in many little pieces. This means at each generation there are relatively few new subdivisions of the parent’s DNA that is passed to a child (average 34), and over several generations many previous segments are not subdivided by crossovers. [NB: in the closest generation – the grandparents DNA passed to us by our parents – the crossovers may be closer to 27 from the father and 41 from the mother, but this difference damps out with as we go back in generations. For the big picture, I’m using an average of 34.

3. Shared DNA follows a 1/4 “rule” with each generation (rather than a 1/2 “rule”). We see this in the average of 880cM with a 1C, and 220cM with a 2C, and 55cM with a 3C, etc. This means the shared DNA drops off quicky with more distant generations. It’s also the reason why we only share DNA with about 1/2 of our 4C and maybe 1/10 of our 5C. However, even given this steep drop off, we have so many 6C to 9C, that we still get shared DNA with a some of them.  Our DNA Match lists are filled with folks who are probably distant cousins…

4. We will almost never see Matches who descend from more than two different children of a distant Ancestor, who share the same (overlapping) DNA segment with us. This one is hard to explain, but it starts with the very low probability that a 7C shares a segment of DNA with us that we each got from the same 6xG grandparent – each of us descending from a different child in that family. Now add to that another Match who shares the same DNA segment with both of us and they descend from a third child in that family. You and a sibling will share about 1/4 of a parent’s DNA. If you add another sibling into the mix, the three of you will only share about 1/8 of a parent’s DNA. Considering the 50/50 chance that a segment will get passed along in the next generation, it gets to be very long odds that you and two Matches will share DNA from a 6xG grandparent’s three children. The science says it’s virtually impossible to add a descendant of a fourth child into a Triangulated Group. I discussed such a scenario in Chapter 1 of “Advanced Genetic Genealogy” and concluded that some Matches with the same TG who descended from 3 different children of the CA probably had mistakes in their genealogy. NB: this “rule” does not preclude multiple Matches in a TG from a distant Ancestor – I have several valid examples of 10 to 20 (or more) Matches from a distant Ancestors. Some of them can be closer cousins to each other, and actually descend from the same child of the distant Ancestor. Also, some of them share different TGs. Bottom line, we won’t see Matches with the same TG descending from more than two children of a CA. I’ll use this “rule” later…

5. The DNA doesn’t play favorites. The DNA process of recombination and crossovers does not have any knowledge of a person’s status, religion, wealth, family size, health, surname, endogamy, etc. etc. The process of recombination is carried out the cell level, without regard to any external factors. So, from the DNA’s perspective, our Ancestors are equivalent. We should expect the same number of segments (TGs) from large or small families; from recent immigrants or Colonial Ancestors; from endogamous family branches or branches without endogamy; etc. However, we can expect a wide range in the number of Matches based on these kinds of factors. But they will not affect the distribution of DNA segments among our Ancestors. The TGs will be distributed randomly – roughly in line with the table above.   

So back to my musings….

I believe my TGs come, on average, from my Ancestors around the 5C level – 4xG grandparent couples. Clearly there will be some type of bell-shaped distribution curve, and some will be a little closer and some more distant. At that level, all of my 16 paternal 4xG grandparent couples would pass down about 193 TG segments, averaging about 12 per couple (Note the 193 in the chart above). Probably an average of 6 on the paternal side and 6 on the maternal side. These TGs have to come from somewhere – meaning 6 TGs, average, from each of the 5xG grandparent couples – either as intact segments and/or through recombination. Each of our results may vary some; but we should see these orders of magnitude (which are not large). The total DNA contribution of DNA segments from all the 5xG grandparents, on one side, will add up to a full set of autosomal chromosomes, on one side.

This is the end of Part 1. In Part 2 I’ll muse more about where TGs are formed and their journey from the Ancestors down to us and our Matches. Part 3 will look at conclusions (what can we learn from all of this), and propose a new spreadsheet to track TGs through other children of our Ancestors (what we can do!).

[15H] Segment-ology: Distribution of TGs – Part 1 by Jim Bartlett 20211001