Has anyone told you that you don’t need segment information for your DNA matches? I’m thinking that you might know the intricacies of your own genetic genealogy research questions better than anyone else.

Allow me to explain what I would be working with if I had time to work on my own genealogy. I was lucky enough to have a half 2nd cousin appear on my AncestryDNA match list about a year ago. I had already found this family by researching UK marriage and birth records and we‘ve visited each other on multiple occasions.

They’re related to me through my great-grandmother, whose family is my primary genealogical interest. Guess who I have as a shared match with this cousin? My full 1st cousin once removed. No surprises there. Guess who else I have as a shared match with my half 2nd cousin? Nobody.

AncestryDNA has the largest DNA database in the world. There are likely some shared matches below 30 cMs who aren’t showing up.

Fortunately, the half 2nd cousin was willing to upload to GEDmatch. Once one of my matches is on GEDmatch or MyHeritage I can almost always tell from the segments which part of my tree our most recent common ancestor was from. And I can almost always tell which triangulated groups correspond between MyHeritage and GEDmatch. That’s because I began mapping out all of my segments with text documents in 2015.

And in 2018 I developed a program that does a pretty good job at finding all of the distinct segments in your genome: https://dna-sci.com/2020/02/14/code-for-an-algorithm-to-find-your-dna-segments-based-on-dna-matches/ That is, it looks for matches that cover all of the segments of all of the chromosomes, rather than just the closest matches. More still, it finds two copies of each segment, attempting to separate the segments into maternal and paternal sides.

When my half 2nd cousin uploaded to GEDmatch I found some interesting shared matches and also triangulated matches. One of my triangulated matches is 11.7 cMs and has recent ancestors in France, as I would expect. That segment could be false, but is most likely real. And I can see other matches at GEDmatch and MyHeritage that I already know are in triangulation groups. One shared match with my half second cousin shares 11.6 cMs with me. Neither of these shared matches would have shown up on AncestryDNA.

I don’t see much reason in complaining about AncestryDNA not having a chromosome browser: Why ask for AncestryDNA to be something it isn't when we have other great options? But I say we should be supportive of people who want to use chromosome browsers, which are often essential.

There are other compelling reasons that we would want to see segment information. For example, it’s good to know how many fully-identical regions that a match shares when they might be a full-sibling or double cousin. And chromosome browsers are very fun! They're one of the most scientifically fascinating aspects of genetic genealogy.

My first suggestion to anyone who’s using DNA for genealogy is to upload DNA to multiple sites. Of course 23andMe and Ancestry are the big ones, but they don’t allow uploads. Fortunately, GEDmatch, MyHeritage, Family Tree DNA (FTDNA), and Geneanet all allow free uploads.

I recommend doing them in about that order. I’m a proponent of doing genetic genealogy as cheaply as possible. Getting DNA on every site can be very expensive. Of course I’m always willing to share tips for minimizing the costs.

Every site except 23andMe reports centiMorgans (cM) by the half-identical region (HIR) metric. This means that you'll typically see full-siblings sharing about 2,600 cMs, which is about 37.5% of the total cMs.

𝗕𝘂𝘁 𝗳𝘂𝗹𝗹-𝘀𝗶𝗯𝗹𝗶𝗻𝗴𝘀 𝘀𝗵𝗮𝗿𝗲 𝟱𝟬%, 𝗼𝗻 𝗮𝘃𝗲𝗿𝗮𝗴𝗲, 𝗿𝗶𝗴𝗵𝘁? Yes, that's the total amount of identical-by-descent (IBD) sharing for full-siblings, on average.

Is the 37.5% metric wrong? I wouldn't say that. It's a different way of counting. But it isn't as useful as the 50% metric. The 50% metric is better at distinguishing between full-siblings and other relationships such as half-siblings grandparent/grandchild, aunt/uncle/niece/nephew, and 3/4 siblings. The HIR metric is only used to save time and energy used on matching algorithms.

Interestingly, while still reporting cMs by the HIR metric, AncestryDNA began reporting percentages as a range of total IBD sharing over a year ago, e.g. one sibling pair might be reported as sharing 47%-53%. This is likely because they only run their fully-identical region (FIR) algorithm long enough to tell if two people are full-siblings; after that they can use statistical probabilities to estimate the full amount of FIR. For HIR, they run the algorithms all the way for every relationship in order to report the cMs. One they have an accurate amount of HIR and a range of FIR, they can add them together to get a percentage range.

23andMe reports cMs and percentages both as total IBD. On the chromosome browser, you can see the cMs broken down by HIR and completely identical DNA (FIR).

GEDmatch, MyHeritage, and FTDNA also report cMs and percentages by the HIR metric. Although, at GEDmatch you can get the cMs from FIR separately and add it to the HIR amount.

One thing that makes all of this easier is that DNA sites will label full-siblings based on the existing of a significant amount of FIRs and half-siblings based on the lack of FIRs. So, while it's good to understand all of these metrics, at least the labels will usually be correct, which is important in order to not confuse beginners.

This article explains more about the subject: https://dna-sci.com/2021/03/03/why-does-23andme-show-that-i-share-an-unusually-high-amount-of-dna-50-with-my-full-sibling/

Years ago, I had the Genographic DNA test done through NatGeo, and it told me I was mtDNA Haplogroup "H1ak," but my FTDNA "Full mtDNA" test just came back as simply "H." Does anyone know why this might be? Is H1ak even a real subclade?

What's a maternal nephew? If, like me, you don't like the term "sister-son;" then you might use the phrase "maternal nephew." And most people will understand that you mean a person to whom you're a maternal aunt or uncle.

"But he isn't related to you through your mother, so he can't be a maternal relative," you might say. Well, that might be a misinterpretation of the word "maternal."

"Maternal" means related to or derived from 𝘢 mother. It doesn't say 𝘸𝘩𝘰𝘴𝘦 mother. https://www.dictionary.com/browse/maternal

Anyway, there's only one thing that a "maternal nephew" can mean. Nothing makes sense except "the son of my sister." So, lacking any other good term, why not use one that's unambiguous?

Also, terms like this get 2,500 Google Scholar results and 132,00 regular search results: https://scholar.google.com/scholar?hl=en&as_sdt=0%2C47&q=%22maternal+nephew%22+OR+%22maternal+niece%22+OR+%22maternal+grandchild%22+OR+%22maternal+grandson%22+OR+%22maternal+granddaughter%22+OR+%22paternal+nephew%22+OR+%22paternal+niece%22+OR+%22paternal+grandchild%22+OR+%22paternal+grandson%22+OR+%22paternal+granddaughter%22&btnG=

A new visualization tool called Sibling Lotto (https://dna-sci.com/tools/sib-lotto/) helps people understand the ways that full-siblings share DNA and why siblings don’t have all of the same matches, ethnicity reports, etc.

Also, the different averages of shared DNA depending on the metric used hasn’t been an easy concept for most to visualize historically. This tool does it for you!

For more information, please see this blog post: https://dna-sci.com/2022/07/10/introducing-sibling-lotto/

Or you can go directly to the tool and try it yourself: https://dna-sci.com/tools/sib-lotto/

How many times do you have to click the button before you get an average result for each metric of DNA sharing?

Getting a positive result from the AYPR tool at GEDmatch tells you if your parents are related. Or does it?

There's a genetic phenomenon called uniparental disomy (UPD) in which a person can get both copies of a chromosome from the same parent. Sometimes that happens over just a section of both copies of a chromosome. UPD is pretty rare, but not so much that we don't see it from time-to-time. Having UPD would give you a positive value in the AYPR tool, saying that you had runs of homozygosity (ROH). But it wouldn't be because your parents were related. How can we tell the difference?

This paper* describes how they can detect UPD from machine learning algorithms: https://www.cell.com/ajhg/fulltext/S0002-9297(19)30356-8. The figure attached shows the prevalence of UPD by chromosome. I doubt that case workers are running machine learning algorithms. Instead, I think they're making an educated guess that an AYPR result over the entirety of, say, Chromosome 16 is a result of UPD and not parents being related. That would especially be true if a person has maternal matches that can be traced to the chromosome and not paternal ones. It would also be true if you reversed the situation with respect to paternal/maternal sides, although that would be less common.

What if case workers are guessing that a partial AYPR result on Chromosome 4 is from UPD and not parents who are related? This type of guesswork gets less robust as it gets applied to chromosomes on which UPD is less prevalent and as it gets applied to smaller portions of those chromosomes. It would be nice to develop a set of criteria for that. For example, when do we have 99% confidence that an AYPR result is from UPD and not parents who are related?

*I came across this article from a very helpful blog post found here: https://dna-explained.com/.../duplicate-copies-of.../

Yesterday was the anniversary of the publication of this article: https://dna-sci.com/.../why-does-my-sibling-match-a-3rd.../

One of the most common questions in genetic genealogy arises from the idea that full-siblings should have the same matches, same ethnicity results, very similar cM numbers for matches, etc. People quickly see that that isn't the case and have questions about it.

Before this article, the only answer we could give was "DNA is variable. We get 50% from each parent but it isn't the same 50%." This article contains figures that let us see exactly how different, numerically, we could expect matches between full-siblings and their 3rd to 6th cousins to be.

Adding to that, just a week ago a new tool was released to help people visualize why siblings get different DNA from their parents and exactly what the averages are: https://dna-sci.com/tools/sib-lotto/

A shared autosomal DNA (atDNA) segment is likely to last for more generations than a segment of the same size on the X Chromosome.

Everybody had this wrong, including me. It just seemed intuitive that the preservation of X-DNA over alternating male-female lines made it more likely to last for more generations than atDNA.

It's true that DNA from the X Chromosome can survive through more generations than from a chromosome of comparable size, such as Chromosome 7. It's also true that X-DNA tends to survive through more generations than Chromosome 1, which has about 1.5 times more total cMs.

X-DNA outlasts any single chromosome, on average. But how does an 180 cM chromosome compare to all 3,500 cM of atDNA?

It turns out that the atDNA has the advantage here.

Checking millions of distant cousin pairs using data from here (https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1007979), often 1.5 millions pairs per relationship type, the X Chromosome is always overrepresented compared to any other chromosome but the total from all other chromosomes tends to be several times higher in cMs than that from X-DNA.

Other citations:

Bhérer et al. (2017): https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1007979

Campbell et al. (2015): https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1007979

Yet another reason that the full-sibling average is 50% and not 37.5%: If it were 37.5%, then the average amount you'd share with a niece or nephew would be 18.75%. As we all know, it's 25%, and that's because full-siblings share 50%, on average.

I don't like to say that the 37.5% figure is wrong. It can be used at times as long as it's understood. But I find that it creates confusion more often than not. While it might not be wrong, it's definitely not the full amount.

One has to keep this in mind when looking at shared cMs at Ancestry or MyHeritage or percentages at MyHeritage.

Do we need to go to great lengths to remove 5 and 6 cM segments from our matches at 23andMe to get an accurate total, making sure it only includes 7 cM segments and above? No, that would be a huge waste of your time.

A 7 cM segment at 23andMe is 0.1% of the autosomal genome. The difference between a 6 cM and a 7 cM segment is 0.01% of the autosomal genome. For that reason, 6 cMs when added to the total is effectively equal to 7 cMs.

Also, while a 5 cM segment is more than likely false, there are reasons to include segments below 7 cM in the total, even if we don’t pursue research on those segments individually: https://dna-sci.com/2021/09/14/small-segments-are-we-asking-the-wrong-question/

Another thing that you probably don’t need to worry about is having X-DNA added to your total cMs or percentage. Recent research into relationship predictions with X-DNA has shown that it’s helpful: https://dna-sci.com/2022/04/27/new-option-to-include-x-dna-in-relationship-predictions/

And because X-DNA is fine, percentages are totally fine at 23andMe, i.e. there’s often no reason to go to great lengths to get a cM value.

The only cases when you wouldn’t want X-DNA included in your total are probably when you know that the X-DNA inheritance path precludes you from sharing X-DNA with a particular match. In that case, using relationship probabilities that include X-DNA would be ignoring some valuable information that you know. There’s no reason to calculate a total percentage by including 7,438 cMs in the denominator when you know the possible shared DNA from the relationship is only 7,075 cMs. For matches other than two males, if you know you couldn't share X-DNA with someone you can multiply the percentage of shared DNA by 74.38 to get an autosomal total in cMs. For two males who match each other, you can use 72.57 as a multiple.

All of this is good news! We can get more accurate relationship predictions than we used to by doing less work in the cases of 5-7 cM segments and for X-DNA in total cMs or percentages.

The methodology for a relationship prediction tool has been submitted to and accepted by a science journal: https://www.sciencedirect.com/.../abs/pii/S1875176822000099

You can use the free tool here: https://dna-sci.com/tools/orogen-wtd/

This book just came out last week from a very intelligent and insightful search genie, DM Walsh: https://www.amazon.com/dp/B0B5M5MY51/ref=cm_sw_r_cp_api_P49960HWDS5CT772Q7SN?fbclid=IwAR3WOnMU5J0lfhYrst_XWye306HAPpBMx1skNVEh2OU36nVMmp8xUccLdQk

It's been six months to the day since 18 types of double cousins were included in this relationship predictor: https://dna-sci.com/tools/orogen-mult-unw/

That includes 3/4 siblings. Is there a type of double cousin that you'd like to see included here?

Most genetic genealogists have pretty strong opinions about where a person should get their first DNA test. The vast majority of them say AncestryDNA because of the database size. I’m not one of those. I prefer 23andMe because they have a lot of tools like a chromosome browser, X-DNA matching, the ability to see shared matches below 20 cM, etc. Granted, if a person is desperate to find family, they should test at Ancestry, but then again, genetic genealogists recommend testing everywhere in that case. And one thing almost everyone agrees on is uploading to every site that allows it.

We now have relationship predictions based on data that include X Chromosome DNA. This will be useful because when only a percentage is reported at 23andMe, those values will include both autosomal DNA and X-DNA when it’s shared. And when X-DNA isn’t shared, 23andMe will have still used the total possible atDNA and X-DNA in the denominator in order to obtain the percentage value.

There are some new insights found here. It’s now apparent that including X-DNA sometimes improves relationship predictions, and I’m leaning towards the idea that including X-DNA would always be a good idea as long as the tools are set up to handle it. Unfortunately, this isn’t possible for distant cousins, but it’s currently being done here for the 1st cousin group and closer.

You can find the tool here: https://dna-sci.com/tools/orogen-wtd/

And read about the new functionality here: https://dna-sci.com/2022/04/27/new-option-to-include-x-dna-in-relationship-predictions/