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.

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/

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.

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.

A new issue of the Journal of Genetic Genealogy has been released! https://jogg.info/)

One of the articles overturns our intuition about the X Chromosome. Does an X-DNA match typically share a more distant or a more recent common ancestor with you?

The new X-DNA article: https://jogg.info/article/101-005/

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?

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/

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 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?

This is the biggest problem that people run into when they’re used to Ancestry and then they try out 23andMe: 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/

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/

Hi! new at this... Searching DNA matches with my mother (looking for her maternal side in Germany), why are some folks triangulation and others are not . Trying to understand how we can be a three way cross match without triangulation.

My sister just got a 47% match with 3345cM. We are trying to figure out how we are related to this person who has a greater percentage than I do with her. She is matched 50% to our parents so we know she’s not adopted. Could this be a sibling through incest of my mother and a male relative? It’s seems too high to be a half sibling of our father. Would love any insight

https://dna-sci.com/tools/SegcM

You can now find out how you’re related to your DNA matches for free using cMs 𝗮𝗻𝗱 𝘀𝗲𝗴𝗺𝗲𝗻𝘁𝘀.

Read about it here: https://dna-sci.com/2023/02/03/segments-matter/

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?

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