Archive | September 2025

23andMe Update

Sep25

23andMe is now owned by​ Anne Wojcicki’s new non-profit The 23andMe Research Institute. An email has gone out to all of us users (see next page) explaining this, which also makes it clear that the focus will be on discovering the health issues in our DNA. Click here for my previous post on 23andme explaining why ​Anne has this interest. 

While crowd sourcing DNA health issues is certainly a worthy cause, it is not the main interest for many of us. Most of my readers consider genetic genealogy a tool to find relatives and uncover family stories.

How the former chromosome browser at 23andme looked comparing a new match to me and my family

The feature I miss the most at 23andme is the chromosome browser that showed ​where my genome matched that of my relatives. Because I have collected an excel file of all my father’s matches with notations as to which I or my brother share, I could frequently tell which family line a new match belonged to,  even a one segment match with no clear relatives in common. ​ Click here for the blog post where I discuss this.

I no longer recommend testing at 23andme unless you want health results or are an adoptee and thus need to test everywhere.

The next page has the text of the email they have sent all of us users.

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Half Sister or Aunt?

Sep18

There are many stories about families where the baby of an unwed teen was passed off as her own mother’s child. A recent query in a FaceBook group asked whether DNA testing could tell whether her aunt, her mother’s much younger presumed sister, was one of those cases, so actually the asker’s half sister. The problem is that the amount of cM shared by those two relationships completely overlaps, roughly 1600-2000 with outliers (click here for the charts at DNApainter).

Known paternal half siblings at DNA-sci

Previously I collected data and studied segment sizes to see how to tell those relationships apart (click here), finding that paternal half siblings will share more larger segments than aunt/uncles. However in this particular case, maternal half siblings, the difference is less clear. Click here for the calculator at DNA-SCI that takes segment sizes into account by using the number of segments. When I tried using it with the numbers of a pair of known paternal half siblings, that calculator predicted that aunt or uncle was more likely (see image). So this approach will not give a clear answer.

A half sister will get half their DNA from their other parent. This will usually result in some close matches that are not shared.  On the other hand, an aunt’s close matches should all be shared with her niece, since they share the same ancestors, so looking at their “not in common” matches might work. The niece, however, is expected to have close matches from her other parent’s side. Here are some half sibling examples from the tool “Match Both or 1 of 2” on GEDmatch:

The kits that match only half sibling A0 and not A5

The kits that match only half sibling A5 and not A0

Notice that each half sibling has a match larger than 200 cM that is not shared with the other. If you have pro tools and access to both accounts on Ancestry, you can also look at this by comparing each person’s list and the matches in common. There is no automated way to do that there yet. Family Tree DNA has a “not in common with” feature, but no other company has it.

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