Finding Genetic Relatives that Have Your Variant Using Ancestry Data
In this Article
- Why Should I Find Genetic Relatives?
- How Do I Find Genetic Relatives?
- What Does Shared DNA Have to Do with Variants?
- How Do I Locate My Variant?
- How Do I Use the Tools Provided by Ancestry Websites?"
Why Should I Find Genetic Relatives?"
Identifying genetic relatives using ancestry DNA tests gives you the opportunity to connect with others who might have your variant. Ancestry DNA tests can help you find people who share similar stretches of DNA with you, and are thus considered to be your genetic relative.
Depending on the DNA you share, genetic relatives might benefit from seeking similar genetic testing and preventative care that you have received. Ancestry tests are not likely to test for a specific disease variant, though. While ancestry DNA tests identify relationships between family members, there are other companies who provide clinical DNA tests that more confidently identify disease variants, and thus are better measures of inherited risk of disease. Therefore, once you have identified at-risk genetic relatives through ancestry DNA tests, it is important that they pursue further medical testing and advice from health care providers.
Once you find genetic relatives who might have inherited a disease variant, you can connect with them.
How Do I Find Genetic Relatives?
There are several companies that do ancestry DNA testing and provide tools for finding genetic relatives. AncestryDNA, MyHeritageDNA, and 23andMe are among the largest and best known. These tests usually do not directly test family-specific disease variants, instead they look at common genetic variants called single nucleotide polymorphisms (SNPs) that are spread across the whole human genome. Even though they do not directly test for your specific variants, the DNA results can help identify relatives who have the same family-specific risk variant.
Communicating with relatives identified through DNA testing may be challenging. The news of possible genetic risk may be known or may be completely unexpected. Please see carefully consider our suggestions and example scripts before proceeding.
Because ancestry tests look for SNPs spread across the genome, they can show who inherited the same large blocks of DNA a common ancestor. We say that there is identity by descent (IBD) for DNA you share with your relatives, because you have inherited the same identical stretch of DNA from the same ancestor. If you share the block of DNA surrounding your variant with a relative, it is much more likely that the relative has the same variant as you. All close relatives share at least some DNA with each other. Finding out who might share a specific variant can be challenging though, as relatives get more distant the chances that they share a specific piece of DNA with you gets smaller and smaller.
Tools offered by various websites allow you to compare DNA across different family members, including yourself.
IMAGE: GENERIC SHARED DNA
The picture above displays chromosomes 5 and 6 for multiple genetic relatives. In this example, seven relatives each had ancestry DNA testing and were identified as sharing DNA. Seven versions of each chromosome are displayed with shared regions highlighted; each version corresponds with each of the seven relatives. This information can be used to assess possible inheritance of a disease variant. The double helix represents the known location of a disease variant, located on on chromosome 5. With this DNA information, these relatives can see which segments of DNA they share. This is usually plotted by chromosome. Each person with a shared DNA segment is colored differently, so that you can easily see who is who.
You can see that the relatives colored orange, dark blue, red, and yellow share the segment of interest on chromosome 5. Relatives colored purple, green and light blue also share DNA, but not at the spot on chromosome 5 where the variant is. Ancestry DNA tests are very unlikely to test for, or display, disease variants. Accordingly, in order to use these tools for connecting about your variant with genetic relatives, you must manually identify the location of your variant. Once you locate your variant, you can find genetic relatives, and connect with them about possible disease risk.
DNA testing companies can show which genetic segments you share with different relatives in different ways. Detailed instructions on how to find this information from different companies is listed below. Before communicating with others about shared risk, it is important to consider how those people may react to learning about this risk. It is also important to understand that people can sometimes chromosomal segments without sharing the same variant.
For more information and guidance about making these connections, read about how to connect with genetic relatives here.
What Does Shared DNA Have to Do with Variants?
If you have identified one or more relative has your variant, you will all share the DNA around that variant as well. Everyone else in your family who has the variant will share the surrounding DNA with everyone else who has the variant. People who do not share the surrounding DNA will not have the variant. This is a good way to find out who does not have your variant, as well as finding out who might have your variant.
It is possible that someone shares a segment that looks like it has your variant, but does not. Usually this is because you have two copies of each chromosome, one from your mom and one from your dad. Sometimes it looks like someone shares the same copy, but they share the copy your inherited from the other parent. Sometimes a relative unexpectedly shares copy from another distant relative that lived before the variant happened. Everyone is connected, if you go back far enough. Some people share random segments for DNA from very distant relatives. One should never assume that because someone shares a specific segment, that they are guaranteed to have a medically important variant. Knowing about shared DNA increases the chances that you share a variant, but it is always important to recommend clinical testing to confirm any suspected risk.
IMAGE: BRIAN AND ALEJANDRO
In the example above, Brian and Alejandro share a segment on chromosome 2 between position 149270710 and 171907571. The variant they are interested in is at chr2:160000000, which is between 149270710 and 171907571. This shows that is on this shared segment. There are two other relatives have an overlapping segment (highlighted in blue and green) these two are likely to share the same variant. Segments can get smaller each generation, so you do not expect them to be exactly the same size. Alejandro and Brian look more closely and find out Brian inherited the variant from his mother. The relative with the segment on chromosome 2 highlighted in blue also shares this DNA with Alejandro and Brian’s mother, so she is likely to have the same variant. The relative with the segment highlighted in green shares this segment with Brian and his father, so she is unlikely to have the variant that Alejandro and Brian are looking for.
It is always important to recommend confirmatory medical testing if you suspect someone has your variant. People can share a segment of DNA without having the same risk variant. In most cases, if someone shares a segment where your variant is they have about a 50% chance of having your variant. This is because you have two copies of each gene, one from your mom and one from our dad. If the variant came from your mom, the relative may be sharing the copy of the gene that you got from your dad. In rare cases the connecting ancestor lived before the mutation that caused the variant happened. In this rare case shared genomic segments do not necessarily mean that a relative has the variant.
There are several suggestions and examples here about how to communicate risk with people who you suspect share genetic risk.
How Do I Locate My Variant?
Find out the genomic location of your variant. Sometimes this is on your report, listed as a chromosome and a long number. If it is not, one way to find genomic location is to look for your variant on ClinVar. You can search ClinVar using any name for your variant, and it will return a chromosome and genomic location. ClinVar willth have 2 genomic locations (Assembly GRCh38 and GRCh37). GRCh37 is the one that is used most often and will be closest to the GEDMatch location.
IMAGE: CLINVAR SEARCH
Once you understand your variant’s location, you can look for this location in shared DNA amongst genetic relatives. Remember, if someone looks like they share the segment where your variant is, they have about a 50% chance of having your variant. You have two copies of each gene, and they may be sharing the other copy of the gene.
If someone share a DNA segment with you and also shares the same segment with other people who you know have your variant, the probability that person has the variant is higher.
How Do I Use the Tools Provided by Ancestry Websites?
The following tools, which all have slightly different features and directions, are available to find shared DNA with genetic relatives. They can be used to check if shared DNA overlaps with your variant’s location:
- You will need to have ancestry genetic data from some company. GEDMatch does not do testing itself. It was built to DNA results from many sources to help people find each other through shared DNA.
- If you have received ancestry genetic data, both you and the other person who has your variant should download DNA data. Instructions for downloading raw data files can be found at Ancestry, MyHeritage, and 23andMe.
- Sign up for GEDMatch. Use the "'one-to-one' compare" tool (video tutorial about how to use this tool). Look for matches that span the genomic location of your variant. On the 2D viewer, the numbers on the bottom are in millions of bases, so chr3: 37,042,537 would be on chromosome 3 at about 37M. In general, ignore pink and blue segments, as these are more likely to be background relatedness from very distant relatives.
- If there is match that is larger than 20 cM at the coordinates of your variant, then it is very likely that you inherited the variant from the same ancestor.
- If you want to look for more relatives you can pay $10 and try the one-to-many comparison tool. This allows you to look for anyone in the GEDMatch database shares a specific segment of DNA.
- Remember people can share a segment of DNA without having the same risk variant. In most cases, if someone share a segment where your variant is they have about a 50% chance of having your variant. It is always important to recommend confirmatory medical testing if you suspect someone has your variant.
- If you were tested using a different company, like AncestryDNA or 23andMe you may be able to upload your DNA data and find people who have done MyHeritageDNA testing.
- After you have your DNA data in the MyHeritage system, on the DNA page click “Tools.”
- One of the tools is “Chromosome Browser.” Select this tool.
- You will now see a list of all genetic relatives in the MyHeritage system.
- You can compare your chromosomes to up to seven other relatives.
- After you have your DNA data in the 23andMe system, on the 23andMe ancestry page click “Find your matches” in the DNA Relatives section.
- You will need to decide what to share and opt in to sharing DNA information with relatives.
- In the page that shows DNA relatives, select a relative. Below the place where you see the shared DNA you have you will see a link to “View DNA Comparison” – Click that link.
- You will now see a list of all genetic relatives. You can select up to 5 additional relatives to compare in addition to the initial relative you selected. Make sure to select yourself as one of the relatives.
- You will get a plot that shows which DNA segments you share with each of these relatives mapped on each of 23 chromosomes. Below the shared segment there are details of the start and end positions of the shared segments. You can go through your relatives 5 at a time looking for people who share the segment with your variant.
- Look for the ThruLines tool in the DNA menu. This will show people who share DNA with different specific ancestors.
- If you already know which parent, grandparent, or great-grandparent had your variant, you can look for others who are descended from the same ancestor.
- If you know someone else who shares your variant and also has AncestryDNA results, you can find them on ThruLines by looking for a common ancestor. If you click o that person ThruLines will list common relatives that both of you share DNA with. This is not all of your common relatives, just those that you both share some DNA with. However, the people listed could share any DNA segment, not necessarily the DNA segment with your variant.
- In order to find if people have the segment with your variant using ThruLines, you would need compare lists and look for people that share DNA with two or three other relatives that you know have the your variant.
Step by Step Guide to Check for Shared DNA with GEDMatch
For an overview, here is a guide about how genetic matching with DNA SNP kits works.
Step by Step Guide to Check for Shared DNA with MyHeritageDNA
Step by Step Guide to Check for Shared DNA with 23andMe
Step by Step Guide to Check for Shared DNA with AncestryDNA
Ancestry DNA does not have a feature that lets users find out which individual segments of DNA they share with relatives yet. If you want to try this you can download your AncestryDNA raw data file and upload it to GEDMatch or MyHeritageDNA. (See the step by step guide to GEDMatch and MyHeritageDNA above for more instructions on what to do after that).
If you want to use AncestryDNA to find relatives with your variant, the information that it gives you about relationships can help.