What’s the use of a chromosome browser?

Ancestry doesn’t have a chromosome browser and I think it’s part of their success. Their idea is to break down genealogy into something easily digestible that the majority of the population can enjoy -no special skills needed.

What happens when someone leaves the protective world of Ancestry and sits at the table with people who have long since left that world (if they were ever in it to begin with) is a lot of confusion. Today I’ve seen multiple questions about chromosome browsers so I thought I’d take a stab at some chromosome browser basics.

First of all, what is a chromosome browser? This is a visual representation of all your chromosomes, of which you have 22 pairs, plus one that is usually included even though it is slightly different. Here it is referred to as number 23, but it is also called the X chromosome. This particular chromosome browser is from FamilyTreeDNA.

I think chromosomes are kind of cute. I love the visual representation of the “pinch” -also known as the centromere, illustrated below where the red dot is (image from Wikipedia).

I’m telling you about the centromere not only because it’s fun to know big words that impress people, but because I’ve seen the question more than once regarding Gedmatch’s chromosome browser (if you don’t know what Gedmatch is here’s a post I wrote about why it’s so useful).

See that vertical pink line right around 123M? That’s how Gedmatch visually represents the centromere. The centromere doesn’t change anything or require you to take anything into account when looking at the chromosome browser, but it’s good to know what it is since it’s being visually represented.

Depending on which company’s browser you are looking at, you will either have to select matches to view on the browser (FTDNA or Gedmatch) or it will automatically appear when you are reviewing a match (23&me or MyHeritage). If you and someone else share DNA, you are related in some way. But how?

The most common question asked is, “how do I know which matches are on my father’s side and which are on my mother’s side?” It’s very important to remember that you have a pair of each chromosome: one you received from your mother, one you received from your father. If you go and look at the picture of the chromosome browser, you are unable to see the pair. That’s because it is unable to distinguish between your maternal and paternal chromosome, so it mashes them up into one. So the short answer is, you can’t tell just by looking at a match on the chromosome browser which side of your family the match is on.

Can you figure out which side of your family a match is on? Yes, I you have another match you can compare it to. For example, if I have an unknown match who is also a match with my great-aunt, SR, then I know that the unknown match must be in the branch of my family tree that I share with SR. If you are coming at this with absolutely no knowledge of your paternal and maternal sides (ie in the case of adoption), you might be able to figure out groups of matches but have no way to assign them to a side. And woe to you if your father and mother come from the same, close-knit ethnic population! We sometimes forget that there are not two but three answers to the “which side” question: father, mother or both.

So what is the use of a chromosome browser? If you and at least two other matches share DNA in the same spot on the same chromosome, that means everyone that matches in that spot share a common ancestor. The group can now work together to see if they can figure out who that ancestor is. Keep in mind that in order for this to work, all three people have to be related to each other (person A has to be related to person B and person C, and person B also has to be related to person C). This is called triangulation. MyHeritage has a nice feature: when you are reviewing a DNA match, you can see a special symbol next to some of your shared DNA matches (circled in red, below). This means that the three of you triangulate.

If you understood all that and you’re interested in learning about how to (imperfectly) do triangulation at FTDNA and how to do it (perfectly) at Gedmatch, you can read my post about that here. If you’re still feeling uncertain about working with your DNA, I’ve got a lot of basics skills posts for you to read; check them out here.

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DNA and privacy

There’s been a lot of news articles and news show segments about DNA testing and privacy, and we all know I feel about that:

What I want to do here is help people make an informed choice about DNA testing, and that means facts, not fearmongering.

There are three basic concerns when it comes to DNA testing: what the company is doing with your DNA results, whether your DNA results can be used against you and the biggest concern, privacy.

First of all, let’s talk about what the company is doing with your DNA results. There is a rumour going around that DNA companies own your DNA once it is submitted, and that they are selling it to third parties. This is an urban legend, so much so that Snopes posted a response to it. The fact is that your DNA is actually being licensed to the DNA company, which you can read more about here (in the particular case of Ancestry).

Second, many people have expressed concern that your DNA results can be used against you. This is especially concerning when it comes to health and life insurance. However, a little research will allow anyone to see that Canada has enacted a Genetic Non-Discrimination Act. This act prevents companies from discriminating against people on the basis of genetic tests or requiring people to undergo genetic testing to obtain services.

  •  (1) It is prohibited for any person to require an individual to undergo a genetic test as a condition of

    • (a) providing goods or services to that individual;

    • (b) entering into or continuing a contract or agreement with that individual; or

    • (c) offering or continuing specific terms or conditions in a contract or agreement with that individual.

  • (2) It is prohibited for any person to refuse to engage in an activity described in any of paragraphs (1)(a) to (c) in respect of an individual on the grounds that the individual has refused to undergo a genetic test.

  • (1) It is prohibited for any person to require an individual to disclose the results of a genetic test as a condition of engaging in an activity described in any of paragraphs 3(1)(a) to (c).

The US has a similar law called the Genetic Information Nondiscrimination Act (GINA). While the American version does not allow discrimination for health insurance, it seems that the same is not true for life insurance. However, this is not the wild west and there are agencies available to help people understand this law and its implications.

A lot of references have been made to Cambridge Analytica when talking about DNA and privacy and I just

It’s a really, really poor analogy. First of all, the information that Cambridge Analytica used was freely given. The word “breach” has been thrown around as if a vault was broken into and its contents stolen. People knew by signing up to Facebook that they were making their information available, much like using my grocery store’s discount card means that I know someone is tracking my purchases. There is a big difference in paying for a service and receiving a service for free: in the first instance your information is something you are paying for, in the second, your information is something you are paying with.

A breach can still happen, however. I am confused, though, at what people think will be done with their DNA. Since our entire genome is not sequenced, it’s not like somebody is going to be cloning us or planting our DNA at crime scenes. Privacy expert Timothy Caulfield states in this article: “If marketers have other pieces, say your search habits, where you live, your education, and they have this piece also, it does create a more comprehensive picture of you.” But if it takes a company millions of dollars, groups of scientists and references populations to give me a best guess at what my ethnicity is, I’m not sure what a more comprehensive picture means, let alone how it would be profitable for companies to do so. Further, so much of what makes us who we are can’t be reduced to our genetics -the old nature vs. nurture debate. Finally, I am extremely skeptical of an article that claims that our genetic information can be used against us in terms of our health insurance but makes no mention of any of the laws mentioned above that prohibit this kind of discrimination.

I don’t like articles like these which hint at privacy bogeymen. While there are many uses for the DNA that has been submitted to DNA testing companies that we have not even thought of, the fact that these articles make inaccurate claims to bolster their arguments and don’t even mention the actual privacy concerns says to me that they are just fearmongering and engaging in sensational journalism.

Let’s talk now about actual privacy concerns. All these DNA testing companies take your DNA and compare it against other DNA to see if they can find a connection. No one can actually see your DNA, just the places in which they match (and in the case of Ancestry, they can only see how much DNA is shared,  not even the place where it is matched). While it is not impossible for people to glean medical information from your DNA results, it can only happen in a very narrow set of circumstances, as in this case, where you know someone has a genetic disease, and so you then know that people who share genes with this person are carriers for this disease.

People also need to be aware that there are many people using DNA to help them find their biological families. Adoptees, birth families and even donor conceived children are using these sites to find matches, gleaning what they can from their family trees and figuring out who their biological family is. Knowing that people can be identified in this way is an important consideration when deciding to take a DNA test. Even those not searching for their birth families are going to use every trick in the book to try to identify their matches to help them further their genealogical research. If you were not aware that things like this could be done, it is important to know. However, the people in the video did not use genetic information at all to identify the match, they used information from social media  as well as other privacy-busting sites, so people should be aware that this privacy concern is not alleviated by avoiding DNA tests.

Given that DNA companies have hit a tipping point in terms of the amount of people who have tested (Ancestry has sold over 10 million kits), it makes sense that people are coming up with new uses for the data stored there. A missing persons case was solved with the use of a database called Gedmatch, and the hope is to solve many more cases that way. However, while Gedmatch’s terms of service state “While the results presented on this site are intended solely for genealogical research, we are unable to guarantee that users will not find other uses,” I don’t know that anyone expected the following use.

A serial killer was recently arrested in California, and law enforcement vaguely stated that a genealogical database was used to collect data that led to his arrest. Two of the big companies have denied that they were a part of the investigation and their terms of service state that law enforcement must follow procedure in order to obtain data (i.e. a warrant must be issued). However, since Gedmatch’s terms of service don’t contain those terms. In fact, Gedmatch itself posted recently:

We understand that the GEDmatch database was used to help identify the Golden State Killer. Although we were not approached by law enforcement or anyone else about this case or about the DNA, it has always been GEDmatch’s policy to inform users that the database could be used for other uses, as set forth in the Site Policy (linked to the login page and https://www.gedmatch.com/policy.php). While the database was created for genealogical research, it is important that GEDmatch participants understand the possible uses of their DNA, including identification of relatives that have committed crimes or were victims of crimes. If you are concerned about non-genealogical uses of your DNA, you should not upload your DNA to the database and/or you should remove DNA that has already been uploaded.To delete your registration contact gedmatch@gmail.com

I hope that Gedmatch’s terms of service will be updated with that language, since while I don’t have a problem with my DNA being used to catch serial killers or solve missing persons cases, some might. Here’s a really good post on the issues.

In the end, informed consent is what it comes down to. No one is suggesting that privacy concerns don’t exist, or that people shouldn’t read the terms and services of the companies that they are sending their data to. However, to single out DNA companies with fearmongering does a disservice to those of us in the genealogy world. While we can use information to diminish the amount of risk we expose ourselves to, zero risk is an impossible dream. People are still using Facebook after Cambridge Analytica (although hopefully a little more carefully) because they see that the value that they receive as a result overshadows the risk. The same is true of DNA testing.

What is the best DNA test?

The old saying goes, “If you don’t know where you’re going, it doesn’t matter how you get there.” The same is true for DNA testing. A better question than “What is the best DNA test?” is “what are my goals for doing a DNA test?” There are a lot of testing companies out there, but I want to focus on the Big 4: Ancestry, FamilyTreeDNA, 23&me and MyHeritage.

The generic answer that is usually given is to test at Ancestry, then do a transfer (copy your DNA file) over to FamilyTreeDNA, MyHeritage and Gedmatch. If you were an adoptee searching for a birth family (or vice versa), this would be the best way to maximize your exposure -basically, you’re leaving breadcrumbs around for people to find you. I would say in this case, if you can swing it, also test at 23&me to fully cover all your bases. You can opt to do just the ancestry testing, which is cheaper than doing the ancestry and health testing.

Are you interested in ethnicity testing? I wrote a post here about how ethnicity estimates are calculated. I don’t know if there is one company that is better than another for a specific ethnicity, although here are some good posts to read for Native American DNA (which may not even show up in your DNA, even if it is in your family tree) and African DNA. You may also be interested to know which testing companies are available in which countries, because if you’re an American looking for your German ancestors it’s probably helpful to know that Ancestry doesn’t currently offer tests in Germany.

If you had questions on your paternal line (father’s father’s father etc), Y DNA testing can be helpful for those with a suitable candidate to test. For men, this can be themselves. For women, a brother, father, father’s brother, or father’s brother’s son will carry the Y DNA of their paternal line. At the moment, FamilyTreeDNA is the only one of the big companies that does this kind of testing and matching, although 23&me does give haplogroups. You can start with a Y-37 test, and later upgrade without having to submit another sample.

Is there ever a reason for doing an mtDNA test? The Y chromosome mutates more often than mtDNA does, which makes mtDNA better at going back thousands of years to find our ancient origins, but less good at figuring out matches in a genealogical timeframe. The only use I can think of is to compare haplogroups (if you are comparing two women and you want to see if they are descended from the same ancestral female) or if you’re interested in your haplogroup as a marker of a particular ethnicity -for example, having an N haplogroup means your mother’s mother’s mother (etc) was of Native origin. Full mtDNA tests are done at FamilyTree DNA and again, 23&me will give your haplogroup.

Finally, if you are interested in doing a DNA test for health reasons (although I’m sceptical of the value in that), currently 23&me is the only one of the big companies to offer that service.

If you’ve already done a test and are wondering who else to get tested, the same question applies. What is your goal? The generic answer is to a) make sure you have someone on both your maternal and paternal side to help you sort through your matches b) test the eldest generations first. This would mean your testing priority is grandparents, great-aunts/uncles, parents, aunts/uncles, then cousins (further than first if you know of any). I don’t think there’s any benefit to testing your children since they have less of your DNA than you do, and if you’re interested in their other parent’s side you can always test the other parent or their relatives in the same priority order.

Don’t touch the settings!

Here is a parable, and like all parables, the point is not if it really happened but the lesson we can learn from it. Once upon a time, someone asked Picasso why he could get away with making art the way he did, and other people could not. Picasso grabbed a piece of paper and a pencil and sketched the most beautiful and perfect picture of a horse. He told the person that once they could make things like that, they were free to break the rules and make art however they wanted.

This is also true in the genealogy world. There are a lot of rules about how to go about doing good genealogy research, especially in the genetic genealogy world. If you want to be successful when you bend or break these rules, you have to know why those rules exist in the first place. I’m going to be talking more specifically in this post about why the Gedmatch settings are the way they are, and why it’s probably not a good idea to change them.

The first setting that people often fool with is the minimum segment size. The default is 7 cM.

I’m hoping everyone knows that a centimorgan (cM) is a unit of measurement used to measure DNA. So why is 7 the default, and why is it a bad idea to lower it?

I talked about identical by descent and identical by chance in my post DNA in a nutshell. I also provided a link to a really good chart that shows the odds that a segment is there by chance or by descent. Once you get below 7 cM, it’s only 50/50 that you share a segment with someone because you’re related to them, and not because you randomly happen to share similar DNA. It’s like comparing Anna Karenina and Hop on Pop and deciding that since they both have the word “the” in them, they must somehow be related. As someone in one of the genetic genealogy Facebook groups said, “lower the settings too much and you’ll match a banana.”

Can this rule be broken? Yes, but the results should still be used with caution. Sometimes people are trying to force a connection that just isn’t there. Perhaps they are worried for reasons covered in my post Is this normal? I’ll repeat (as many times as needed), once you get past second cousins, it is possible not to share DNA with a cousin. It doesn’t mean anything is out of the ordinary. I explain why in my post We all have two family trees. If you really, really want to find a matching segment with a cousin because they are on your brick wall line, you are more than welcome to try, but the burden of proof still rests on you to prove that that segment actually came from that ancestor that you share, and not because you randomly happened to have the same DNA in that spot (the odds are more in the favour of randomness). You might be pursuing this segment in this spot as if it is a real match and assume that whoever matches you there must be from the line you share. You could invest a lot of time and energy pursuing this match, only to find out that you’ve been on a wild goose chase. But hey, I pursue matches that are likely to be outside of the genealogical time frame, so I guess we’re all allowed to be masochists in our own way.

The other settings (there are actually a few of them) are for SNP counts. I don’t know why anyone would want to change these since very few people actually know what SNPs are (most people pronounce it like ‘snips’). Here’s what I know about SNPs. DNA testing does not test all our DNA. That kind of testing (although available) is still pretty expensive and it’s unknown whether doing so would provide us with better results. In my post Are DNA tests accurate? I wrote a how 99.9% of the DNA people share is identical (we also share 60% of our DNA with a banana, so I wasn’t kidding about lowering the settings too much). What a DNA test does is look at specific points where the DNA is likely to be different. These points are called SNPs. Some parts of our DNA have more of these points than do other parts. Therefore, if you know which parts are SNP-rich, you could consider lowering the cM value while raising the SNP value to compensate.

Or maybe, just maybe, you could consider leaving the settings where they are.

Are DNA tests accurate?

Thanks to talk shows, a lot of junk science, pseudoscience and a general misunderstanding of how science works is proliferating. Wine is good for you wine will kill you coffee is bad for you coffee is good for you fat is bad except sugar is worse than fat and on and on and on…

What’s someone to make of all this? In general, I think it leads people to think that science is just another opinion and not based in truth. And I’m not saying that science doesn’t have its problems (highly recommend the book “Inferior” by Angela Saini), but the terrible way in which science is being communicated to the public is causing a lot of problems. I’m not here to talk about how vaccine preventable diseases are on the rise, however, I’m here to talk about the science of DNA tests, because this is me when someone tells me that they heard that they aren’t accurate.

On the other hand, this is me when people are asking why their DNA ethnicity estimates are wrong:

On the one hand, I want to defend the science behind them, but on the other, I want to explain the weakness of the science behind them. You see my problem?

So let’s take a look at how ethnicity estimates are done and why yours might be wrong, and hopefully by the end we’ll have a greater appreciation for the science involved.

The first thing we have to understand is that DNA is made up of only 4 letters. Imagine if our alphabet only contained four letters and someone had to write different books using only these letters. A lot of books will share words, but we don’t have a problem distinguishing between like “Hop on Pop” and “Anna Karenina.” In reality, the way in which these four letters combine makes proteins that make up everything with DNA -plants, animals, and people (yes, your food has DNA in it. Not just GMO food, all food). I think most people know that we are very closely genetically related to chimps, but did you know we share 60% of our DNA with a banana? Our DNA is 99.9% similar to everyone else in the world, so the science behind figuring out how that 0.1% is different from person to person is pretty mind-boggling, when you think about it. It’s like if a random word was changed on random pages of “Anna Karenina.”

So how do we distinguish the 0.1% of DNA that is different between people and make categories based on those distinctions? The first thing that has to be done in order for ethnicity estimates to define an ethnicity. Here’s where it gets tricky. How do you define an ethnicity? For example, what does it mean when we say someone is English, or German, or Swedish? When you look at the Earth from space, you don’t see borders – not to mention that the countries and their borders have been changing since their creation. My great-grandmother came from Galicia, which was part of the Austro-Hungarian Empire. Currently the town she was from is part of Poland. Whose to say her DNA is significantly different from another person’s in a town just over the border in the Ukraine? Further, people have always been on the move. I may know where my ancestors were 100 years ago, or even 400 years ago, but it’s possible that my DNA came from a time frame beyond even that.

Let’s say we are able to decide what defines a particular ethnicity. The next step is to create what’s called a reference population. Basically, a group of people is put together whose family is documented to have lived in the area for a really long time. The assumption is that the DNA that these people share is in some way similar and is also distinguishable from people whose families have lived in other areas for a very long time. Keep in mind that this group of people is different from testing company to testing company. This is why every testing company’s ethnicity estimate will vary, even with the same person’s DNA.

Alright, now we have a whole lot of DNA from all over the world to compare your DNA to. This is not the DNA of people who USED to live in the area your family is from, this is DNA of people who currently live in the area where you’re from. We’re making an assumption that as long as we check that the families of these people have lived there for long enough that it’s the same thing.

If you’re like me, you will fall into more than one ethnicity category. Another member of a Facebook group I’m a part of described it as a recipe. Basically, you’re a mixture of several different kinds of soup. The testing company is going to try to separate out your carrot soup from your noodle soup from your borscht and compare it to their recipe for each kind of soup (keeping in mind that their recipe is slightly different from another testing company’s recipe). It’s about as complicated as unbaking a cake. Did this carrot come from the carrot soup or the noodle soup? We’re not really sure where this part of the soup came from, but it looks kind of similar to a vichyssoise so we’ll call it that.

Your ethnicity estimate can be inaccurate, yes, because it is based on several assumptions

1) that a particular ethnicity can be defined

2) that a particular reference population can be created based on this ethnicity

3) that the reference population has DNA that is similar to other people from that ethnicity and different from people not of that ethnicity

4) that the DNA of people whose families have lived in that region for a long time is the same as the DNA of the people who used to live in that region

4) that your DNA can be decomposed and assigned to various ethnicities based on how similar it is to the reference population’s DNA

Those are a lot of assumptions. I’m hoping you can see how impressive it is that there’s an entire science based on this, and that this science is getting better and more accurate. But…it’s not soup yet.

What’s the takeaway from this? For one, you should adjust your expectations as to what ethnicity estimates are capable of telling you and to what degree of accuracy. For two, ignore small percentages unless you have a documented paper trail to back them up. And lastly, DNA is about a lot more than ethnicity estimates. If you did a DNA test just for that then you are missing out on all the fun the rest of us are having connecting with new cousins and trying to figure out which segment of DNA came from which ancestor.

We all have two family trees

I read somewhere that 50% of people do a DNA test for the ethnicity estimate. Which probably explains why 50% of the questions in the Facebook genetic genealogy groups I’m a part of start with “I did a DNA test and why does it say I’m X when I’m not X?” Or conversely, “why doesn’t it show any X ethnicity when I was told I had X ethnicity?” (with X almost always being Native American).

The questions that are not about ethnicity are usually along the lines of “is this normal?” Most people don’t know that up to 10% of third cousins and 90% of fifth cousins don’t share any DNA. This post is going to explore why we don’t see ethnicities we think we should see, and why we don’t share DNA with all our more distant cousins. I’ll talk more about how ethnicity estimates work in another post.

Did you know you actually have two family trees? Genealogists use the term “paper tree” to refer to ancestors you can trace back using traditional genealogical methods, such as birth, death, marriage and census records. The term “genetic tree” refers to ancestors you inherited DNA from. Obviously, there’s a lot of overlap there, but your genetic tree is only a small subset of your paper tree. Given that we can only have as much DNA as we can have, there’s just not enough room to have a piece of every single ancestor’s DNA. Further, even if you inherited a piece of DNA from a particular ancestor, it is possible that the segment is too small to be useful. If you read my post “DNA in a Nutshell,” you will understand that once a segment gets too small, it’s entirely possible that it matches another person who has that segment totally by chance, and not because you share a common ancestor. I imagine that when comparisons are made for ethnicity estimates, the same idea holds true. Tiny amounts of DNA that match a particular company’s reference population for a particular ethnicity are likely not counted.

Obviously, if your genetic tree contradicts your paper tree, there’s an issue that needs to be resolved. For example, if you don’t share DNA with a close cousin, or you don’t share DNA in the expected range, someone’s paper tree is going to have to be updated. But absence of evidence is not evidence. Not sharing DNA with a more distant cousin or not having a particular ethnicity show up in your estimate does not mean that your paper tree is incorrect. If it’s DNA proof you’re looking for, finding a relative who matches you as they should and also matches a particular cousin and/or has the particular ethnicity show up will do -a great-aunt or uncle works well here if there isn’t a grandparent, an aunt or uncle if there isn’t a parent. People who are only half-related to you (like a cousin) are not really good candidates, because they might have inherited those segments from an ancestor you don’t share, but it’s better than nothing if there’s no one else to test. If the DNA is on a straight maternal or paternal line, mt DNA or Y DNA testing will assign you a haplogroup. You can use this information to see if your haplogroup is consistent with haplogroup of a particular ethnicity.

To sum up, your genetic tree is only a small part of your paper tree, so while it’s disappointing to not match with certain cousins or to not have a particular ethnicity show up in your estimate, it doesn’t mean there’s something incorrect in your paper tree. Maybe Native American DNA is just not that into you.

DNA in a Nutshell, Part 2

I watched this amazing video from the Rootstech 2018 conference and it made me feel that my post DNA in a Nutshell was incomplete. In that introductory post I talked about how we inherit DNA and provided a link  that has some great pictures. Even if you don’t want to read the article, looking at the pictures can really give you a good idea of how we get the DNA that we get.

One thing people understand about DNA is that if we share it, we’re related. Many people might not realize that if you don’t share DNA with someone, it doesn’t mean you aren’t related. According to the ISOGG wiki, Up to 10% of 3rd cousins (people who share great-great-grandparents) and up to half of 4th cousins (people who share great-great-great-grandparents) do not share any common DNA. As the DNA gets mixed up and handed down, it’s possible you didn’t inherit any of the DNA a particular ancestor had, but a cousin did. It’s also possible that you both have DNA from a particular ancestor, but that it is not the same DNA in the same spot. The algorithms that the companies run don’t know that your segment on chromosome 2 and your third cousin’s segment on chromosome 6 came from the same great-great-grandparent. You and your third cousin may be related, but if you don’t carry the same segments, the computer will never know it. This is important to know when it comes to understanding the intermediate topic of triangulation.

The use of the term “cousin” by companies is a very liberal one. When I see the term “cousin” used for matches I like to think  of it as generations rather than as a reference to a specific person. Since it is an estimate based on the amount of DNA you share, and the amount of DNA people in a particular relationship can vary, a 1st cousin can refer to an actual first cousin, a great-aunt/uncle, or even a first cousin once or twice removed. The further you get past close family (parents, siblings, aunts/uncles, nieces/nephews) it becomes much harder to pin down the actual relationship you share with a given DNA match.

Besides the difficulties of a varying range of DNA assigned to particular relationships, as mentioned in the previous post, things like half-relationships (where you only have one common ancestor rather than a common ancestral couple) as well as endogamy (where you might be related to someone in more than one way) and pedigree collapse (where you have intermarriage in your family tree) can make relationships look closer when the actual common ancestor is actually much further away than suggested. And since every company does their calculations differently about what counts towards the total amount of DNA you share with someone, different companies may give different results and some may conclude that you aren’t actually related to someone while another company says you are.

All this to say is that you shouldn’t worry if you are new to all this and everything isn’t as precise and exact as you expected. If you don’t share DNA with a third cousin who has also tested their DNA, it doesn’t necessarily mean something is amiss. If your testing company says your great-aunt is your 1st cousin, it’s not because your great-aunt is actually your 1st cousin. If you find a DNA match and your testing company says this person is your second cousin, but you can’t see the overlap in both of your trees, you may have to dig further back.  Let go of the expectation of certainty and embrace the variety.