Archives

Ancestry and the Longest Segment

Aug30

All the DNA testing companies, except Ancestry, show you a chromosome map of the segments you share with a DNA match. For the casual user those maps, called chromosome browsers, may not be of interest. However those of us with intermarried families among our ancestors (endogamy) need to see the segments in common in order to know if a match is a findable relative who shares large chunks of DNA with us or just someone who shares multiple distant ancestors. Third cousins and closer family will always share some large segments, at least 20 or 30 centimorgans and even larger for closer relatives (see Blaine’s chart below).

Ancestry now shows the longest segment on a DNA match’s profile page which could be very useful to help decide which matches to pursue and which ones to ignore.

A known fourth cousin on my Norwegian line with some endogamy, notice how much larger his largest segment is than the size of the match

A word of warning, the size of the largest segment that they show is uncut, that is it is listed before they remove matching DNA that is expected to be population specific. For example, many of my one segment matches show a longest segment that is larger than the match size as shown above! If you click on the longest segment number there is a very informative popup about relationships and segments that includes this statement:

“In some cases, the length of the longest shared segment is greater than the total length of shared DNA. This is because we adjust the length of shared DNA to reflect DNA that is most likely shared from a recent ancestor. Sometimes, DNA can be shared for reasons other than recent ancestry, such as when two people share the same ethnicity or are from the same regions.”

A Jewish match not to pursue, likely related many times since the largest segment is 15

My often requested advice for Ashkenazi Jewish researchers is to look for one segment greater than 20cM and another greater than 10cM plus several others in order for a DNA match to be recently related enough to find the common ancestor(s). Therefore it would be even better if Ancestry showed the two largest segments. Subtracting the largest segment from the total to figure out the sizes of the other segments is not very accurate since the total is adjusted by removing population specific sections (Timber algorithm) while the largest is not.

Blaine Bettinger includes the longest segment in his DNA statistics collection form and below is a chart of those 2015 results by cousin level; click here for his blog post.

Chart of longest segment statistics collected by Blaine Bettinger. Click it for the full article

I spent some time looking at the cases where matches are tested at both Ancestry and 23andme in my family’s results.

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My Thoughts on the Changes at Ancestry

Aug1

Drop down menu from messages icon top right, red arrow added by me

The changes to my messages on Ancestry are more of a problem for me than the upcoming changes to small matches. Most of the major bloggers have weighed in with their opinions about Ancestry removing matches of less than 8 cM to people not starred, grouped, or messaged. So I will list some of those articles at the end of this one. Fortunately the date for this change has been moved from early August to late August.

Personally I do not have a strong opinion about small segments. For my family, those matches are not at all useful, so I pay them no attention. About half of them rate to be false matches anyway, although Ancestry has good algorithms for phasing, making more of them real than elsewhere. However I do understand that small matches can be important to people looking into deeper ancestry. Note that I have never used those very small matches even when solving unknown parentage cases.

The other upcoming changes to segment information like showing the size of the largest segment and using decimals for the centimorgans (cM) instead of rounding to the nearest whole number are clear improvements. [UPDATE 30-Aug-2020: the longest segment is here. Click here for my blog post about it.]

However my messages, carefully filed into 50 folders, have just been converted to the new system months after everyone else’s. One major annoyance is that every message thread was suddenly marked unread, all 64 of them! I had previously read almost all of them (only 4 listed unread on my icon). At least they gave me the option to download my old folders of messages.

My Messages look like this now, red arrow is my addition

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New Ancestry DNA Feature: Connecting Matches to Your Tree

Apr22

New Icon: Match connected to Tree

 

Ancestry has unveiled a new convenient feature: the ability to link a DNA match to their entry in your tree. No one can see the resulting tag but you or someone with whom you have shared your DNA results.

In the past, I would add the pathway to the relationship in the notes for a match. Below is how the match to my second cousin John looks now. The tree icon with a check next to his name means that I have connected this match to my tree. Clicking on that icon will take you to a view of him within my tree. On the right you can see how I explained his connection to me in the notes next to the notepad icon.

Over in your tree, each person that has been connected to a DNA match also has that icon on their image. Here is how my brother looks in the pedigree view in my tree now with the new icon next to a green leaf. People I have shared BOTH my tree and DNA with can also see that icon but not on the living unless they specifically have permission to see living people in your tree. Also they have to have turned on “connected DNA Matches” from the DNA icon at the bottom of the far left tower of icons. That icon is only there when a DNA test is connected to that tree. Clicking it slides in a panel on the right where you can select which DNA icons you want to see. For example, since I have turned on the ThruLines indicator, my parents and grandparents have the ThruLines icon showing in the image below.

Pedigree view of my brother, yellow arrow pointing to the DNA icon added by me

Why is this useful you may ask? Well for me it is most useful on those distant cousins with no trees whose relationship I figured out a while back and have probably forgotten the details of by now. Or maybe Ancestry found it for me and I added that family branch to my tree (click here for my post for how to easily do that).

Since I have shared both my DNA and my tree with my brother and a few interested cousins, they can look at my match list for those icons to see if I have already figured out how a newly found cousin connects to us.

The other time I have found this new feature to be really useful is when I have a research tree for an unknown parentage case and have built out the tree of a match as a floating branch within that tree to much more depth than they had in their own tree. Now I can connect those matches so that I can quickly click to see what I have built for them.

Here is the step by step of how to set up a connection with this new tool using my brother as an example.

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How to Share Ancestry DNA Results

Jan29

Sharing DNA results at Ancestry.com is very useful when you want to see how much your relative shares with other relatives. All that this sharing allows you is the ability to see their match list, their ThruLines, and their ethnicity results, not their raw DNA nor the ability to download it.

Being able to see a cousin’s ethnicity may help figure out which side of the family that Finnish DNA is from or whatever puzzling ancestry you are interested in. Seeing their match list can be extremely useful for solving a mystery or just for the fun process of collecting family data.

For years I have been referring my cousins to an old blog post kindly written by genetic genealogist Angie Bush which explained how to initiate a share. However by now the screen shots are long out of date, so here is a new step by step for this process created by sharing my results with my brother.

1. Go to your DNA home page by clicking on Your DNA Results Summary in the drop down menu under DNA in the top menu (see my pink arrow)

2. Click on Settings at the top right of the page (another pink arrow)

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Can ethnicity help with unknown parentage?

Dec5

Recently ethnicity was a major factor in figuring out the family of the mystery father of an Australian women of mixed heritage: Chinese, Italian, and English/Irish.[UPDATE 4-APR-2020: no help needed, all resolved now.]We still need some help, so any Australian readers please read to the end.

Elana’s ethnicty on Ancestry after the update, before she had lots more Italian

This case is unusual because for those of us with primarily European ancestry, the ethnicity predictions from the various DNA test companies are not accurate enough to be a significant aid with figuring out unknown parentage situations. For one thing, our ancestors moved around more than you might expect, and for another, the science is just not exact enough yet.

Too often I get a panicked email or comment from someone who is worried that Daddy is not their dad, or perhaps grandad is not, because their ethnicity predictions show no German or French or Bulgarian which he was and where is that Norwegian from? To which I respond, check your matches, if you have matches to cousins from his family, all is well, it’s just the inaccuracy of ethnicity predictions. North Europeans and South Europeans are fairly distinct from each other, but countries as we know them today did not exist in the far past.

Comparing ethnicities for Elana (left) and her mother (right) at Ancestry

In Elana’s case, having East Asian and Southern European in addition to the usual Australian British mix, actually gave us some different and potentially useful data to work with. Her mother seemed entirely English, Welsh, Scottish and Irish, a frequent blend for an Australian. She remembers that Elana’s father said he was part Maori and that his name was Bob. There is no Maori in her results shown above (it usually looks Polynesian), so likely he was just trying to make himself seem exotic and interesting.

Elana’s best matches at ancestry were almost all maternal (yes this is a squashed image)

Since Elana’s mother tested also, we could see that Elana had no close matches that were not listed as “Mother’s side” on Ancestry which made the search very difficult. Her paternal matches consisted of only one 3rd cousin, an American of Italian ancestry, and lots of 4th cousins, quite a few with trees, and most of the closer ones were of Italian descent, in spite of only 7% Italian listed in her Ancestry ethnicity.

One possibility for so few paternal matches was related parents. We checked that by uploading to GEDmatch.com (click here for my post on related parents) and that was not the case. The other more likely explanation was very few of her father’s relatives had tested. For example, Elana had only one very distant Asian match in spite of her father clearly having half that heritage.

Since we could see both Elana’s ethnicity and her mother’s it was easy to tell that Elana’s unknown father was half Chinese/Korean with an Italian (great) grandparent. These were her initial percentages before the recent update at Ancestry:

65% England/Scotland/Wales (so her father will have about 15%)
16% Korea and Northern China
12% China
7% Italy

I asked Elana to also test at 23andme and to upload her Ancestry results to MyHeritage and Family Tree DNA as well. Still no luck finding close paternal matches.

 

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