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Getting your close family members tested is immensely useful when trying to sort out your Relative Finder matches. Close relatives share some of your DNA, and they will share some of your relatives as well.

It’s very straightforward when a family member shares the same relative in common as you do, like this.

In this case, my paternal first cousin shares the same segment with the same relative as I do. This provides clear evidence that this relative is related to me on my paternal side.

However, sometimes you can make a conclusion about which side a relative comes from even when a family member does not share the relative.

Let’s say I want to try to figure out which side of my family this relative is on. Although I have lots of relatives tested, to keep things simple, I am going to pretend that the only person I have available to use is my paternal half-sister Kim.

The first step is to take note of the segment’s location. This segment is on chromosome 2, and has a start point of 140.000.000 and an end point of 151.000.000.

The next step is to take a look at how I match my half-sister at that spot on chromosome 2 (this info is found using the ‘View in a Table’ feature in Family Inheritance: Advanced).I need to check and see if Kim and I share DNA at the same spot as my 5th cousin and I do. And we do — Kim and I have a shared segment that goes from position 129.000.000 to 181.000.000, which definitely encapsulates the segment that I share with my 5th cousin (140.000.000-151.000.000). This means that I can make a conclusion about which side of my family this match comes from. (Please note that if Kim and I did not share a segment at the same spot that I match my relative, no conclusion could be made).

I know that I have two copies of chromosome two, one from my mom, and one from my dad. Kim and I got the same chunk of DNA on chromosome 2 from my dad (I know this because Kim and I are related only through my dad and not my mom). Therefore, if Kim also shares this match with me, this relative is on my dad’s side. This is not the case — Kim does not share this relative with me. Therefore I know this relative is not on my dad’s copy of chromosome 2. The only other possibility is that this relative is on my mom’s copy of chromosome two, and therefore I know that this relative is related to me on my mom’s side.

You can sort out which parent your Relative Finder match came from by using collateral relatives that are related to one of your parents but not the other. Close relatives in this category include half-siblings, aunts and uncles, and first cousins. Siblings do not work for this because they are related to both of your parents and all four of your grandparents, just like you are. Therefore any shared DNA and shared relatives that you have with your sibling could have originated with either parent.

You can sort out which grandparent your Relative Finder match came from by using collateral relatives that are related to only one of your grandparents. Close relatives in this category include half first cousins or first cousins once removed, second cousins, great-aunts and great-uncles, and a variety of other relatives.

If you have a more distant relative tested, like a first cousin twice removed or something like that, it’s possible to narrow down which great-grandparent a match comes from, and so on.

Also, if you have direct ancestors tested, the process is very similar to what I outlined above and in fact in some cases it’s a little simpler. If you’ve got one of your parents tested, let’s say your mom, and your Relative Finder match does not match your mom, you can reasonably conclude that the relative is on your dad’s side. If you have a grandparent tested, and the Relative Finder match is not shared with your grandparent, you would follow the same checking-the-segments procedure that I outlined with Kim.

This method isn’t perfect — it’s possible to have a ‘false positive’ match — this means that your Relative Finder match does not match either one of your parents. It’s also possible that a testing error, such as a miscall, will prevent a legitimate relative from properly showing a shared segment. But for the most part, comparing the segments like I outlined above should work for you. The larger the segment, the more accurate using this method is.

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You can also use the knowledge that you get ONE chromosome from mom and ONE chromosome from dad to your advantage when trying to sort out your relatives. What this means is that at any given spot in the genome, you share DNA with one and only one of your maternal ancestors and one and only one of your paternal ancestors.

I will use my pedigree as an example:

If I share DNA with, let’s say, my grandfather Ernest Badger, at a certain spot in the genome, I know for sure that I do not share DNA with my grandmother Audra Woodward at that same spot.

Graphically illustrated, this is what it looks like. At any given location, you can share DNA with one paternal grandparent or the other, but not both. You can share DNA with one maternal grandparent or the other, but not both.

Let’s take a look at an example Relative Finder match. Andrea, Kim, Kelly, and Hailey are the four daughters of my dad. Aletha is our paternal aunt and Leona is our paternal first cousin once removed. Using the tools I’ve outlined above, let’s see what we can find out regarding the side of our family that these relatives come from.

I told you earlier that aunts can sort out which parent a match comes from, and first cousins once removed can sort out which grandparent. So we know that our match ‘Jack’ comes from our dad’s side, and our match ‘David’ comes from our paternal grandfather’s side (because Leona is related only to our paternal grandfather, and not our paternal grandmother).

We don’t have to stop here, though. By using the ‘ONE piece of DNA = ONE ancestor’ rule and by visualizing the chromosomes, we can make another conclusion — we can decide which grandparent our match Jack comes from.

Here’s a sketch of my dad’s chromosome 17 at the relevant spot.

Now let’s look back at our Relative Finder matches. Andrea, Kim, and Kelly all have the same relative and therefore the same piece of DNA. Hailey has the same relative and therefore the same chunk of DNA as our paternal first cousin once removed, and this cousin is related only to our paternal grandfather, my dad’s dad. Therefore, Hailey got the ‘blue’ piece of DNA.

So here’s what we have so far.

Let’s think about this for a minute. We know several things.

1. Every child inherited a piece of that DNA from dad.

2. Andrea, Kim, and Kelly inherited one piece, and Hailey inherited the other piece.

3. Hailey inherited the blue piece.

This leads us to our conclusion — Andrea, Kim, and Kelly inherited the ‘green’ piece of DNA, the piece from my dad’s mom (our paternal grandmother). We can now conclude that our Relative Finder match ‘Jack’ is related to us on our paternal grandmother’s side.

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I hope this mini-tutorial was not too hard to understand! The number of Relative Finder matches you are able to sort and the types of conclusions you are able to make will vary depending on which family members you have tested on 23andMe. If you have any questions, need any clarification, or want me to look at a specific situation in your family, please leave a comment or email me at

I was looking at my site’s traffic, and I notice that an awful lot of people find my website by googling questions about the DNA shared between siblings.

I thought it might be useful to answer some of these questions and clear a few things up.

“What percent of my DNA is the same as my sister’s?”
“How much of my DNA is shared with a sibling?”
“How much DNA should brothers and sisters share?”

The short answer is that siblings share an average of 50% of their DNA.

Here’s why siblings share 50% of their DNA.

Your mom has two copies of every piece of DNA and your dad also has two copies. To make a child, each parent passes on one copy of their DNA – consequentially, the child will also have two copies of that piece of DNA.

I have drawn an example below.

Let’s say that on this particular piece of DNA, you are outcome #3 – ‘green and purple’. You got a ‘green’ copy of DNA from your mom and a ‘purple’ copy from your dad.

Your parents can produce a child with any one of the four combinations that I drew. Take a look at how the four possible outcomes compare to your outcome (green and purple).

There is a one out of four chance (25%) that a new child of your parents would have an identical match as you (that is to say, they would also get a green gene from mom and a purple gene from dad).

There is a two out of four chance that the new child would be only half-identical to you. If the child was outcome #1, they would have an identical gene from your dad (purple) but a different gene from your mom (red instead of green like you). Outcome #4 is the same except reversed. Your sibling would have an identical gene from your mom (green) but a different gene from your dad (blue instead of purple).

There is a one out of four chance that the sibling would inherit a different copy of both genes. This is what happens with outcome #2. This sibling got a red copy of your mom’s DNA, while you got a green copy. He also got a blue copy of your dad’s DNA, while you got a purple copy instead.

To summarize, at any given point in the genome, there is one way to be fully identical with your sibling, two ways to be half-identical, and one way to be non-identical.

Said another way, across the entire genome, you will share about ¼ of your DNA fully identical with your sibling. You will share about ½ of your DNA half-identical with your sibling, and about ¼ of your DNA will be non-identical compared to your sibling.

25% identical DNA (100% match – same from mom AND dad) = .25 * 100 = 25%

50% half-identical DNA (50% match – same from mom OR dad but not both) = .50 * 50 = 25%

25% not identical DNA (0% match – different from both mom and dad) = .25 * 0 = 0%

25% + 25% + 0% = 50%. Siblings share an average of 50% of their DNA.

Okay, I’ll rephrase this: “Why do I only share 45% with my sister?”

50% is only an average percentage. This percentage can and does vary quite a bit. On the thread that I started on 23andMe about shared DNA percentages with relatives (23andMe members can read that thread here) the highest reported sibling percentage was 58.27% and the lowest was 40.99%. Sharing 45% with a sibling is lower than average, but it’s nothing unusual.“Will my siblings get the same 23andMe results?”

Not really.

Some aspects of your 23andMe results will be the same – for example, your maternal and paternal haplogroups.

Most of your results will not be the same as your sibling’s results, because, like we discussed earlier, you and your sibling each get a unique combination of DNA from your parents. Your health results will most likely be somewhat similar, but they will not be identical. Same with Relative Finder – your results will be similar. Because you share ~50% of your DNA with a sibling, you will share roughly half of your relatives in common with your sibling (but around half will be different for each person).

“Can one sibling have a closer DNA match to the parents than the other one?”

Sort of. It depends on what you mean by ‘closer DNA match’. Every child gets a complement of 23 chromosomes from each parent — this does not vary. However, a father passes along a Y sex chromosome to a son, and an X sex chromosome to a daughter. In terms of size, the X chromosome (left) is a lot bigger than the Y chromosome (right). You could say, based on this size difference, that a father gives more DNA to his daughter compared to his son, and that therefore a daughter has a closer match to her father than her brother does. Some companies, such as 23andMe, will report that a man shares ~47% of DNA with his son and ~50% with his daughter. So in this respect, you could say that one sibling has a closer DNA match to the parent than the other sibling does.

However, something to keep in mind is that the parent-child relationship does not vary like other relationships do. For example, we already talked about the wide range of percentages that siblings can share (on my thread, they share anywhere from about 41% to 58%). Parents and children do not vary like this — it’s always 50% from mom, 50% from dad (or 53% from mom/47% from dad for a son, when taking into account the size difference of the sex chromosomes).

“Can DNA test if you are full sisters without the parents?”
“Can sisters determine if they are true sisters through DNA testing, even if both parents are dead?”

Yes, definitely.

Sibling relationships are very unambiguous, with or without the parents.

On 23andMe, sibling comparisons look like this. The percentage of DNA shared is approximately 50% and there are both fully-identical segments and half-identical segments (as well as some non-identical segments). No parents are needed to identify a sibling relationship on 23andMe.

For what it’s worth, here’s what a half-sibling comparison looks like.For the most part, half-siblings share only half-identical segments — no fully-identical segments. (An exception to this rule would be seen with maternal half-brothers on the X chromosome. Men have only one X chromosome, so any match between two men on the X would show as fully-identical.)

Also, here’s what a comparison between two unrelated people looks like.It’s blank, with no shared segments.

You can see that these various outcomes are very distinctive from one another. 23andMe can definitively determine whether two people are full siblings or not.

I hope this helps answer some of your questions about siblings and their shared DNA! If you’ve got a question for me, leave a comment or email me at 

I recently got results for my dad’s second cousin.

Here is how Ron matches with his second cousins — nothing unusual here. Second cousins are expected to share about 3.125% of their DNA, and everyone shares approximately this amount with Ron.

Things start to get weird when looking at the comparisons between Ron and my three sisters and I. We are second cousins 1x removed, and would be expected to share about 1.5% of our DNA.

One of my sisters has a fairly normal match to Ron, although her percentage is slightly above average. Surprisingly, she passed on every single segment perfectly intact to one of her daughters. Her other daughter got most of the segments — she shares about 70% of the DNA Ron shares with her mother compared to the expected 50%.

My dad’s other three children have only a very small match to Ron. We share about three or four times less DNA than expected. These results are more consistent with a fourth cousin as opposed to a second cousin 1x removed.

After looking at this comparison, it might be tempting to conclude that because we have such a small match compared to the average percentage for second cousins 1x removed, our dad probably had a smaller than average match too.

However, there is no evidence to suggest this.

If you add up all the unique segments that my dad’s four daughters inherited from him, it’s 13 + 43 + 38 + 29.5 + 18.5 + 44 = 186 cM = at least 2.48% of DNA shared between my dad and Ron (there’s also a decent chance that Ron and my dad shared segments that none of his daughters happened to inherit). This percentage is slightly below average for second cousins (2.48% compared to 3.125%), but not dramatically low.

However I only received 26 out of 186 cMs, or about 14% of Ron’s shared DNA compared to the expected 50%. My sister inherited a piddly 13cM out of 186cM, or about 7% of the shared DNA. Sister #3 inherited 30 cM out of 186 (16% of the shared DNA). Sister #4 seems to be skewed in the other direction — she inherited 157cM out of 186cM (84% of the shared DNA).

Can I coin a ‘new’ saying?

“Recombination is like a box of chocolates, you never know what ya gonna get!”

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Jason Woodward and Dorotha Drew Woodward, our common ancestors.
Thanks for the DNA!

I recently got DNA results for my dad’s paternal first cousin. She is the daughter of my dad’s father’s brother, making her my first cousin once removed.

The percentages of DNA that she shares with our relatives are all over the map. I found these results fascinating because it shows that recombination is random & incredibly hard to predict.

Leona, my dad’s first cousin, has two first cousins that have also tested their DNA, Dan and Aletha. The theoretical percentage shared by first cousins is 12.5%. Dan and Aletha both deviate from this percentage – Aletha shares more than expected, while Dan shares less. This kind of variation is pretty common and not unexpected.

Things start to get more extreme when I look at the comparisons between Leona and my three sisters & I.

One of my sisters shares more than twice as much DNA with Leona as my other sister.
 

Leona and my sisters and I are first cousins once removed, and are therefore expected to share only half the amount of DNA as first cousins (6.25%).
However, Leona actually shares more DNA with one of my sisters than she does with her true first cousin. This is pretty odd – it just goes to show that recombination is often very hard to predict.

The comparison between Leona and my sister and her two daughters further demonstrates this fact. My sister and Leona are first cousins once removed – this relationship has an expected theoretical percentage of 6.25%. My sister’s children and Leona are first cousins twice removed – this relationship has an expected theoretical percentage of 3.125%.

My sister has a slightly lower than expected percentage of shared DNA with Leona – 5.28% as compared to the expected 6.25%. A mother passes on 50% of her DNA to her children, so it would be fair to assume that the children should share about 2.64% with Leona. This is not what we see, however. By random chance, one of her daughters happened to inherit much more than 50% of the shared DNA, while the other daughter happened to inherit much less.
 

Even though her mother shares less than expected with Leona, daughter number one inherited a large percentage of Leona’s shared DNA from her mother (about 60% rather than 50%). As a result, her percentage with Leona is almost identical to the theoretical percentage for first cousins twice removed – 3.10% compared to the expected 3.125%.

In contrast, daughter number two inherited hardly any of her mother’s shared DNA with Leona. (about 20% rather than 50%). As a result she shares only about one third of the expected percentage – 1.16% compared to the expected 3.125%. 23andMe predicts that they are third to fourth cousins because they share such a small percentage of DNA.

I have really enjoyed looking at our comparisons — I think it is very interesting the way it can vary so much! Please comment if you have any questions or need any clarification.
I recently got my v3 (version 3) results from 23andMe. It is the latest technology — there are now 1 million SNPs tested versus about 500,000 on the older version. There are a couple of new health results (namely Alzheimer’s & the APOEgene) available on the new chip, and my comparisons with my relatives did change slightly, but overall things stayed about the same.Here’s how my v3 results compare with my v2 results.

I show up as an identical twin to myself, tee-hee. This speaks to the accuracy of the test provided by 23andMe — when the test is repeated, you get the exact same results.


Here is an example of how a health result changed. Here is what my result for “Coronary Heart Disease” looks like on my v2 profile (the old results):

My v3 results are slightly different:

They have changed because more SNPs are available.

 

 

The v2 results are on the left and the v3 results are on the right. It might be hard to see, but the little black circles on the v2 results say “NG” for “not genotyped.” This means that not all of the SNPs used in the coronary heart disease report are available on the v2 platform (which makes sense because the v2 chip has fewer SNPs than the v3 chip). But all of the SNPs are available on the v3 chip, and so this refined information is why my results are a little different.

Let’s move to the ancestry section now.

For most of my close relatives, my comparison has changed slightly.

Here is my DNA comparison with my sister (who was genotyped on v2) — here is how she matches with both my “v2 self” and my “v3 self.” The biggest change was that what appeared to be two segments on chromosome 10 has changed to one segment on my v3 profile. A couple of other segments have also changed, and overall, my percentage of DNA shared with my sister dropped by about one half of one percent. All segments that have changed are circled in red.

 

 

Here are my DNA comparisons with my two half-sisters (both genotyped on v2). In both cases, there have been some small changes. For both of my half-sisters, what appeared to be two segments (with a small break in between) on chromosome 13 has changed into one segment. The percentage of DNA that I share with my half-sisters decreased very slightly.

 

 

Here are my DNA results with my half-sister’s two daughters (my half-nieces). They were genotyped on v3. In this case, the results barely changed at all. Two segments are ever-so-slightly different (by only a few SNPs), but overall the percentages of DNA that I share with them remain virtually unchanged.

 

 

Here are my DNA results with my paternal aunt and my paternal cousin. They are both on v2. I could find no discernible difference in the DNA shared with my paternal aunt, although the percentage of DNA shared did slightly change. The percentage of DNA shared with my cousin also changed very slightly, and one segment is a little bit different.

 

 

Here are my DNA results with my maternal uncle and my maternal aunt. My maternal uncle was genotyped on v3 while my aunt is on v2. My results with my maternal uncle did not change at all, while my results with my maternal aunt changed slightly on one segment.

 

 

Here are my DNA results for my maternal great-uncle and my maternal great-aunt. They are both on v2. I could find no discernible differences in the segments, although the percentage of DNA I share with my great-uncle did change slightly.

 

Overall, I saw very few changes.
The most dramatic change was with my sister — I suspect perhaps this is because I share both fully-identical and half-identical segments with her (I am related to all of my other relatives on only one side of my family, so I share only half-identical segments with them). Not sure, though — it could just be a coincidence.

My more distant relatives from Relative Finder stayed the same for the most part, but there were some slight changes. I gained two relatives that weren’t there on the v2 chip (as far as I can tell, I did not lose any). Of my existing 203 relatives that I am sharing with, the percentages stayed the same with only a few exceptions. A few segments changed only very slightly, like this:

10 of my relatives either gained or lost .01%, and one lost .02%. So no dramatic differences here — for 192 of my relatives the percentages stayed exactly the same.
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I think that about summarizes my v2 profile versus my v3 profile. Overall, there are not a whole lot of differences except for the new Alzheimer’s report and the APOE info. New health results are coming in every month though, so perhaps in the future there will be more new features on the v3 chip that are not seen on the v2 chip.

Here it is! It’s about all the benefits that genetic genealogy has to offer. I wrote about my experiences with 23andme.com!

Well, since I last posted about 23andme a lot has changed. I have had several of my close relatives tested. Also, the customer database of 23andme has dramatically increased in size. When I first got my results, I had only 214 cousins on the website, but as of today I have 657! During the past year, I have found out several interesting things about my genetic ancestry and I have also been able to confirm eight generations of my Napier line.

I am planning to write about all of my experiences soon, but for today I thought I would do a post about my close relatives and just summarize who I asked to take the test and why I wanted them to get tested.

Here is my full sister and how much DNA I share with her as well as the number of segments that we have in common. Siblings are expected to share about 50% of their DNA — my sister and I share slightly more than expected, just by random chance.

Getting your siblings tested at 23andme is very useful because they will have DNA (and relatives along that DNA) that you do not have. You can see that I share 53% of my DNA with my sister, but that leaves 47% that we do not share.

Overall, 269 genetic cousins on 23andme have accepted contact with me & my sister. We both share DNA with 77 of them. Then there are 100 relatives that I share DNA with, but she does not. There are also 92 relatives that she shares DNA with, but I do not. If I did not have her tested, I would have missed out on these 92 relatives.

So to summarize, if you don’t have parents available to test (mine are deceased), siblings are invaluable because they have DNA from your parents that you don’t have.

However, getting your sibling tested will tell you nothing about which side of your family a 23andme cousin comes from. After all, by definition, your sibling shares the same parents (and grandparents, etc etc) that you have.

To try to narrow down which side of your family a 23andme cousin comes from, you have to turn to relatives that you have from only one side of your family.

I have had my two half-sisters, my dad’s double cousin, my paternal aunt, my maternal aunt, my maternal uncle, my maternal great-uncle, and my maternal great-aunt tested.

Here is my comparison with my two half-sisters.

The theoretical percentage shared between half-siblings is 25%. You can see that I share more than expected with one sister and less than expected with the other. Again, there’s no real rhyme or reason for this, it’s just random chance.

Getting my half-sisters tested allowed me to sort out which of my parents many of my relative finder cousins came from. The “con” of testing half-siblings, though, is that they will have many matches that you do not have because you have only one parent in common.

Here is my comparison with my aunts and my uncle.

The theoretical percentage shared between an aunt/uncle and a niece/nephew is also 25%, the same as half-siblings. You can see that I share almost that exact amount with my two aunts, but slightly more with my uncle.

The difference between your half-siblings and your aunts & uncles, in terms of DNA testing, is that you are related to all of the 23andme cousins that your aunts and uncles have. Even if you don’t share a DNA connection with them, you are genealogically related because your aunts and uncles don’t have any ancestors that you don’t have. Your half-siblings do.

So to a greater degree than with my half-siblings, I can identify relatives and make a genealogical connection with someone, even if I personally do not share any DNA with that person.

I have also had my maternal great-uncle as well as my maternal great-aunt tested (my grandmother’s siblings).

The theoretical percentage here is 12.5%. You can see that I share a bit less than expected with each one.

Getting my great-aunt and great-uncle tested has been very useful because it allows me to identify many relatives that come from my maternal grandmother’s side of the family. And what I said before applies to this relationship too — even if I don’t personally share DNA with all of the 23andme cousins that they have, they are still my relatives because my great-aunt & great-uncle do not have any ancestors that I do not have.

And last but not least, I have tested my dad’s double cousin.

I wrote in a previous post about what a double cousin is, as well as more info about the double cousins in my family. But I will summarize here — double cousins share all four of their grandparents in common rather than just two. This occurs when two siblings from one family marry two siblings from another family.

My dad would be expected to share 25% with all of his double cousins. As his daughter, I have half of his DNA and therefore I would be expected to share half as much — 12.5%. You can see that I share a little more than expected with this particular cousin.

Double cousins are pretty rare, especially nowadays, but they are very useful in terms of DNA testing because (as with aunts & uncles) all of their relatives are your relatives because they have no ancestors that you don’t have. He also helps me to identify which parent my 23andme cousins come from.

I hope this was a good summary of the family that I have on 23andme and what I have learned from all of them. If you have any questions about my family or about 23andme in general, please let me know🙂

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