What is a Genetic Family Tree?

Family trees are a great visual representation of the people we are descended from and those we are related to. Some may be small whilst others can be epic tomes of family history connections. There can also be different types of family tree as well.

In this post we are going to look at a family tree type that may be slightly different to what you are used to. Genetic family trees offer a slightly different perspective of our family than a standard tree so read on to find out more.

What Is a Genetic Family Tree?

When it comes to the genetic family tree there is a very big clue in the name that should immediately tell you what it is. Essentially our genetic family tree features only individuals from whom we inherited DNA or share DNA with.

In order to make it into our genetic family tree the individual must share genetic material with us beyond the 99.9% that all humans share anyway. This makes the genetic family tree far different from your standard genealogical family tree.

What Is a Genealogical Family Tree?

The genealogical family tree contains all individuals that we have determined by personal knowledge or research are related to us. This would include ancestors as far back as we can find them as well as distant cousins who although we are related may not share DNA with us.

A genealogical family tree potentially knows no limits and could include relations by marriage or adopted family. We can allow ourselves a little latitude when it comes to a genealogical family tree because after all sometimes family is more than blood.

Why Are Genetic Family Trees Different to Genealogical Family Trees?

The main difference between genetic and genealogical family trees is that we do not share DNA with every person in our genealogical tree. In the genealogical tree we will find all of our known family living or dead regardless of relationship distance.

In the genetic family tree we should only find people with whom we definitely share some amount of DNA. As an example the genealogical family tree may include a 10x great grandparent who although they are a proven ancestor would probably not have passed any DNA down to us.

This is because recombination of DNA generation after generation means that we share less and less DNA with ancestors the more generations we are separated from them. You would not find a 10 x great grandparent in a genetic family tree as there is no way to confirm that you would have shared DNA with them.

Essentially a genetic family tree will be vastly smaller than a genealogical one. You would not mention relatives by marriage such as in-laws, step parents and the like.

Will All Your Living Relatives Be in Your Genetic Family Tree?

You might think the answer to this question would be a definite yes but you would actually be wrong. Without question parents, grandparents, siblings, aunts, uncles, close cousins etc will be in your genetic family tree as long as they are blood relatives.

What many of us forget however is that we have literally thousands if not millions of distant cousins who are alive today. We could be standing in line at the grocery store behind a sixth cousin and not even know it.

It is highly likely that that cousin we do not even know will not share DNA with us. This does not make them any the less a cousin because they share a common ancestor with us. So technically they are a living relative who could appear in a genealogical family tree but if they do not share DNA with us they do not make the genetic tree cut.

Who Definitely Belongs in a Genetic Family Tree?

Essentially to be included in your genetic family tree the individual needs to be a close blood relative. The list of definite relatives would include:

  • Mother & Father
  • Full and half-siblings
  • First & second cousins
  • First & second cousins once removed
  • Aunts & uncles
  • Grandparents
  • Great grandparents

It should be noted that second cousins once removed or half second cousins once removed do have the potential to not share DNA with you. This is because the genetic connection is closer to third cousins. Third cousins are the first level of cousin that you have a definite risk of not sharing DNA with.

The list above mentions your closest family but you can also have more distant cousins in your genetic tree if you can confirm you share DNA with them. Around 90% of your third cousins are likely to share DNA with you while 50% of your fourth cousins will also share some of your DNA.

As we get to more distant cousins you will find fewer of your cousins actually share DNA with you. As an example we only share DNA with about 20% of our fifth cousins. They would be perfectly placed in a genealogical family tree but unless they are one of the 20% with whom you share DNA they can’t be in your genetic family tree.

The truth is not all of our cousins will have taken a DNA test and there are thousands of them out there. You may locate fourth and fifth cousins only by the fact you are a match on Ancestry or some other testing website.

If you find them as cousins based on a DNA match and you can confirm their connection to you then all those family members between them and you can be included in your genetic tree. This would include the common ancestor with whom you share common DNA and the line of individuals between that common ancestor and the cousin match.

Do You Need to Know the Connection to Include a Distant Cousin in Your Genetic Family Tree?

This is an interesting thing to consider. Let's say you have a cousin match who is fifth – eighth cousin as an estimate. They share a small amount of DNA with you and likely share a common ancestor. Technically they could be included in your genetic family tree.

There is a problem though because they have no listed family tree and you have no idea how you are connected to this person. Realistically you need to be able to link that cousin to you to be able to place them in your genetic family tree.

To add this distant cousin without relationship context would just lead to a cluttered and confusing tree. You should probably not add them but you could make a list of these DNA matching cousins in the hope of one day discovering the connection.

Are All of Your Ancestors on Your Genetic Family Tree?

The answer to this is that nowhere near all of your ancestors will be found in a genetic family tree. As already mentioned the genetic family tree requires proof of a DNA connection. To a certain level we can infer that we definitely share DNA with closer ancestors.

The further back in our tree the less likely it is we share DNA with our ancestors. We may discover a living cousin match who descends from a common known ancestor and this confirmation means we do indeed share genes with that person. We of course would not be able to DNA test this long dead ancestor but the cousin match shows there is DNA from them in both of you.

Why Don’t We Inherit DNA from All Our Ancestors?

You may be wondering why we do not always inherit DNA from our more distant ancestors, surely their genetic material is passed down to us. The reason for this is a matter of DNA recombination but let me first step back a second to illustrate a point.

In theory, as we inherit roughly 50% of our DNA from each of our parents you would think we would get 25% of our DNA from each of our grandparents. The math seems logical and solid enough but that old DNA does not want to play ball.

You see we get 50% of our DNA from our father who himself got half of his DNA from each of his parents. This is where the fly hits the ointment because the 50% of our DNA that we get from dad is not a 50/50 split of his parents DNA.

We may receive 22% from our paternal grandmother and 28% from our paternal grandfather. It still equals 50% roughly but random recombination of DNA within our parents means we do not get equal amounts from our grandparents.

This happens in each generation with the disparity becoming larger the further back we go. Within a few generations we start to have ancestors from whom we receive no DNA at all. Their DNA may be in our parents but it is not part of the DNA that parent passes down to us.

So Is the Genetic Family Tree Our “Real” Tree?

The answer to this is somewhat subjective because a genetic tree without a doubt only features relatives with whom we share DNA. It is therefore more accurate and the connections in it are generally beyond reproach.

That said, the genetic tree is not a full and proper representation of our tree. We have distant ancestors and cousins who are very much related to us but just may not share DNA with us. Our 4 x great grandfather may have not passed DNA down to us but he is still an ancestor without whom we would not exist.

So realistically speaking the genetic family tree is not our “real” family tree as it does not factor in blood relatives who we just do not share DNA with.

How Do We Build Our Genetic Family Tree?

If you want to build a genetic family tree then DNA testing is very important. Now it can be assumed that your parents and grandparents are DNA matches to you as can siblings, uncles, aunts and close cousins.

In order to fill in more distant relatives you will have to test with one or more DNA testing companies such as AncestryDNA, 23andMe and familyTreeDNA. This will give you access to cousin matches who you can trace back to common ancestors.

As mentioned by confirming a common ancestor with a match you can include that ancestor and the individuals who form this link in your genetic family tree.

Conclusion

The genetic family tree solely focuses on individuals that you share genetic material with. You do not include relatives by marriage and some of your more distant ancestors and cousins may also not be in this tree.

It is a representation of the people that you share DNA with but does not cover legitimate blood relatives who you do not share genetic connections with.

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  • " What is a Genetic Family Tree?". NameCensus.com. Accessed on October 5, 2022. https://namecensus.com/blog/what-is-a-genetic-family-tree/.

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