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What is Phasing in DNA Results?

Has anyone ever suggested that you phase your DNA? In this post, learn what phasing is in DNA results, and how you can use this technique to learn more from your DNA matches.

Phasing is one of those terms that sounds hard to do, and perhaps even like a complicated scientific term, but it really isn’t. Once you are done reading this article, you will have a new tool in your genealogy toolbox.

What is Phasing in DNA Results

Before we get started with the discussion about phasing, it is important to know that all humans have two copies of all 23 of their chromosomes. One copy of every chromosome came from our mother, and the other copy came from our father.

Our maternal and paternal copies of each chromosome contain genetic information that our parents inherited from their ancestors through their parents. This means that our DNA is full of information from both sides of our family because it is inherited in essentially equal parts from both mom and dad.

We can see the results of all of this genetic data in our results from autosomal DNA testing companies like Ancestry, 23andMe, and MyHeritage, through our ethnicity estimate and DNA matches.

Even though we know that one copy of each chromosome came from our maternal line and the other from the paternal ancestors, it is challenging to figure out exactly which copy of each chromosome came from which parent. This is where phasing comes into play.

What is the definition of phasing in DNA results

Explained simply, phasing in DNA results means sorting the copies of each chromosome into two distinct maternal and paternal sets. This phrase is most often used to describe assigning alleles, which are contained on our chromosomes, to DNA that is inherited through the process of recombination.

As you read earlier in this article, each copy of our chromosomes is inherited from our mother and father and is made up of DNA that was inherited from their parents. A child only inherits 50% of each of their parent’s DNA, which means that both mom and dad’s two copies of every chromosome must be recombined into a brand-new copy for the child.

The DNA that is included in the unique copy of the each chromosome passed down to the child is randomly selected during a process called “recombination”.

The process of recombination is very interesting because it explains why we do not share DNA with all of our ancestors, or share DNA with all of our relatives. While we inherit 50% of our parents’ DNA, there is 50% left behind that we don’t inherit.

The information contained within our two copies of each chromosome inherited from our parents can help us explore our ancestry in two different ways. Our ethnicity estimate can help us learn where in the world our ancestors may have lived during their lives, and our DNA matches can help us learn more about specific ancestors as well as other people in our family tree.

Without the ability to phase our chromosome copies into maternal and paternal groups, however, we are limited in what we can learn from our DNA. Fortunately, there are several methods, tools, and strategies that we can employ to phase our chromosomes for ethnicity data and to sort DNA matches.

Parental phasing of DNA matches

Parental phasing of DNA matches is a pretty simple concept, even though the name sounds technical. All it means is to sort DNA matches, or our genetic relatives, into paternal and maternal groups.

By sorting our DNA matches into groups, we can more easily identify where to look for a common shared ancestor with each individual DNA match. Once we know how we are related to our DNA match, we can add them and their ancestors to our family tree and potentially learn more about unknown ancestors.

Sounds pretty good, right?

The other benefit of phasing our DNA matches is that it helps eliminate false DNA matches. Sometimes we can share small “coincidentally identical” DNA segments with other people, but by sorting our matches into groups of people who also share DNA with our parent, we can reduce the chance that we are researching matches who are not really related to us.

Do any DNA testing companies phase matches automatically?

If your parents have also tested their DNA with the same company that you have, then you are able to see “phased”, or sorted, matches on your DNA match list. I have included brief instructions on how to “phase” your matches for each company below.

Phased matches by parent on Ancestry

If you and one or both of your parents have taken a DNA test on Ancestry, then you can view your matches automatically phased by parent on your DNA match list. Click “Groups” at the top of your list, and then you should be able to choose “Mother’s side” or “Father’s side”.

Once you choose a parent, then the matches will automatically filter out to only show you those matches who are related to you on that side of your family.

If you don’t have a parent that has tested, but you do have a close relative, such as an aunt, uncle, grandparent, or half-sibling, you can view your shared matches on Ancestry. This is not exactly the same as phasing by parent, but it performs a similar function.

Phased matches by parent on 23andMe

If you and one or both of your parents have taken a DNA test on 23andMe, you can filter your list to include only those matches who also share DNA with your mother or father. This option is on the left side of the screen (desktop view).

Simply choose “Mother’s side” or “Father’s side”. Then, you will be able to see a list of your DNA relatives who also match the selected parent shown in order by strength of relationship.

Phasing on Gedmatch

Gedmatch is a site that has many DNA analysis tools that we can use to learn more about our ancestors. There is a utility on the site that allows users to phase their DNA matches by parent if they have access to the DNA data of at least one parent.

Many of the tools are free, but the Phasing tool is only available for Tier 1 subscribers.

Gedmatch is not a DNA testing site, so we must download our DNA from the company that we tested with and upload our data file to Gedmatch to access the tools. This is a fairly quick process, and we can begin using the tools almost right away.

The DNA file of our parent or parents must also be uploaded to Gedmatch in order to use this tool.

Phasing of ethnicity data

Phasing of ethnicity data, or determining which copy (i.e. maternal vs. paternal) of our chromosome matches the regions on one’s ethnicity estimate, can help us figure out where in our family tree we might need to look to find an ancestor who passed down DNA matching specific regions of the world to us.

The ethnicity estimate is one of the most popular regions that people take DNA tests, since it is an easy-to-understand snapshot into where our ancestors came from. However, it can be tricky to know for sure which region came from which parent.

This is where the phasing of ethnicity or ancestry information comes in handy. It can be a bit tricky to figure out, however, which leads many people to ask whether it can be done automatically.

For example, why can’t the DNA testing companies just figure this out for us?

Automatic phasing of ethnicity information by parent

Ancestry is currently offers the only DNA test that can automatically sort our ethnicity data by parent if they have not taken a DNA test. This allows you to see exactly how much DNA matching each region on your estimate came from each of your parents, even if your parents have not tested their DNA.

This is done for every customer and is visible on the Ethnicity Inheritance or SideView results on your DNA Story, which is page where you can see your detailed ethnicity estimate. This information is visible even for those customers who tested their DNA years ago, so definitely check to see your updated results if you haven’t looked at them in a while.

Can you phase ethnicity data manually?

Yes, with a bit of research and time, you can figure out which portions of your chromosomes came from specific ancestors. This information can help you identify which copy of each chromosome came from your mother and father.

This strategy of DNA research is called chromosome mapping. A very neat website named DNA Painter allows us to “paint” our chromosomes with this segment data to help us visualize our two copies of each chromosome and identify which segments were passed down from specific ancestors.

Some companies, such as 23andMe, allow you to download ethnicity inheritance data by segment. DNA Painter allows us to import this data into our chromosome map.

This may allow some researchers to determine ancestry inheritance by chromosome copy.

Conclusion

I hope that this post has helped you understand everything that you needed to know about the basics of phasing, and how you can use it to learn more about your DNA results. It’s great for looking at your ethnicity estimate in greater detail, as well as exploring your DNA matches more efficiently.

If you have any questions about something that you read in this post, or if you would like to ask a specific question about phasing, I would love to hear from you in the discussion below.

Thanks for stopping by today!

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Shelley S

Wednesday 21st of September 2022

Would you say the Leeds Method and Genetic Affairs and such grouping methods "phase" your matches?

Mike Barry

Monday 15th of August 2022

Thank you for the informative article about Phasing autosomal DNA results, it was a good high level view. However as an experience researchers fluent in the use and manipulation of the various types of DNA test now available, I think that some important technicalities were omitted, in that the reason that we even have to think about phasing is that the testing companies do NOT sort the two results per base into paternal or maternal. Yes its true that Gedmatch has some useful tools and the phasing tool being one, BUT you can only use the resulting kit within Gedmatch, i.e. no down loading to use else where, or just to understand what they have done. The best situation for a starting point in a family is to test both parents and as many of your siblings that you can, but as also mentioned missing parent & child phasing is a useful tool as well and many people searching for lost or unknown bio parents can use this method to separated a known parents contributions both donated and Non donated, AND the donated from the missing parent, finally the child subject will also have a resultant phased kit made up from each parents donated 50%. So if you missed the process the missing parent kit will only be 50% from one phasing process, and this is where the subjects sibling come in, for each extra child phased then the percentage of the unknown parents donations increases significantly. Going back to the known full family scenario, of both parents being tested then the three individuals will have a phased kits as the out come. Some of the benefits of using phased kits in matching were mentioned, and even if you can't get the kits out of Gedmatch then having them there is a good thing. If you are interested to know more and actually do your own phasing it is straight forward to do in MsExcel given some caveats like the best outcome will be from results from the same generation of testing equipment at the same testing company, and in excel you are comparing on a line by line basis so the bases need to be the same before proceeding. There are now alternative on line Genertic Tools available and I would recommend Kevin Borland's on line offering, which will also accept the 50% phased kits for the missing parent situation. Lastly it is possible to get nominal 50% kits into Gedmatch as a research kit, BUT you can only compere with single other kits, but the one to one outputs are useful. I hope this has expanded the discussion a little more.

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