DNA Beginnings: What is a Match?

Earlier than we consider matches at every of the 4 main distributors, FamilyTreeDNA, MyHeritage, Ancestry and 23andMe, let’s focus on what a DNA match is, what it means, and what it does NOT imply.

A Match to One other Individual

Every of the 4 main distributors, however not another distributors, present matches to you and different people of their database.

This instance from FamilyTreeDNA exhibits my mom’s match listing itemizing me as her closest match, together with a equipment I uploaded from Ancestry once I was not too long ago updating upload/download article instructions for my readers. You don’t have to add a number of kits to distributors.

Each vendor’s match listing seems completely different, as is the data they supply. We’ll cowl every vendor’s match listing individually in future articles on this DNA Beginnings sequence.

Every vendor has completely different standards for matching, however in essence, utilizing that vendor’s match standards – your DNA and the DNA of an individual you match are equivalent on a piece of DNA of a vendor-defined size.

Every of these distributors identifies the individuals who match one another and opt-in to matching in a technique or one other,

Whenever you signal on to your account at every vendor, you’ll see a match listing. Every of these individuals on that listing match your DNA:

  • At or above the vendor-defined centiMorgan (cM) threshold. You’ll be able to read more about centiMorgans here.
  • At or above the vendor-defined SNP threshold, which means the quantity particular person contiguous matching places.

Every vendor has their very own thresholds and inside algorithms that outline matches. For instance, a match of 8 cM with 1500 SNPs refers to each the size of the match (cM) and the density of places inside that phase of DNA that match between two individuals. Solely matches above every vendor’s threshold seem in your match listing.

Matches smaller than or beneath these vendor thresholds are thought-about much less more likely to be legitimate matches, so are excluded and don’t seem in your match listing.

Imputation Impacts Matching

Completely different distributors take a look at their clients’ DNA on completely different DNA chips:

  • Completely different chips take a look at a special quantity of DNA, however usually roughly 700,000 SNP places
  • That 700K places of DNA may be in numerous places in your genome

In different phrases, simply because two distributors each take a look at 700,000 places doesn’t imply they take a look at the identical 700,000 places.

Even the identical vendor will, over time, implement completely different DNA testing chips or modify the SNP places examined on the identical chip.

These completely different chips, chip variations and SNP places will not be totally suitable with one another, so the distributors use a method often known as imputation to stage the taking part in subject between non-identical information.

That is notably related for distributors that settle for uploads from different distributors.

On this instance, we’ve 3 distributors and 10 completely different SNPs, or DNA places.

  • Vendor 1, on their first Model 1 chip, examined places 1-8.
  • Vendor 1, on their second V2 chip, examined places 3-10.

Due to this fact solely 6 places, 3-8, have been “frequent” between these two completely different chips utilized by the identical vendor.

  • Vendor 2, on but a special DNA testing chip model (V3) examined places 1-4 and 7-10.
  • Vendor 3 on chip model V4 examined places 2-5, 7, 8 and 10.

There are solely 4 places out of 10 examined by all of the distributors’ chips.

If the seller’s match standards is that 10 places in a row should match, then none of those individuals will match one another.

Generally variations happen due to chip variations, and generally a distinction happens as a result of a location doesn’t learn nicely for some cause.

As a way to compensate for the variations in DNA places examined/reported, a method known as imputation is broadly used.

Imputation makes use of scientific likelihood methods to fill within the blanks based mostly on DNA that usually neighbors or “travels with” the nucleotides or DNA values, (T, A, C or G), discovered within the buyer being examined.

Imputation permits all of these blanks to be stuffed in for all clients for every of these 10 places, assuming the “lacking DNA” is near examined DNA places.

It’s due to imputation that clients can obtain their uncooked DNA information from one vendor and add to a different for matching, despite the fact that the distributors don’t use the identical precise chip.

Generally imputation is inaccurate. Matching may be affected in each instructions, which means that some individuals will probably be on one another’s match lists who truly don’t match on a specific phase. Others would truly match if all of these places have been examined.

The best high quality matches are between individuals who examined on the similar vendor, on the identical chip or at two completely different distributors who use precisely the identical chip. Nevertheless, that’s typically not potential and isn’t throughout the management of the client.

False Optimistic Matches

This interprets to, “You’re a match however not likely” and is a headache for genealogists.

False constructive matches present as a match between two individuals on their match lists, however they aren’t truly legitimate matches for family tree.

  • A false constructive match might happen because of imputation, in fact.
  • A false constructive match might additionally happen as a result of the 2 individuals match as a result of a part of the DNA of their mom and a part of the DNA of their father at these places simply occurs to mix to seem as a match.

For functions of those examples, presume that every of those matches exceeds the seller’s match standards so can be proven in your match listing.

In our instance, Individual 1 and Individual 2 match in any respect 10 places, in order that they would seem on one another’s match lists.

Nevertheless, if we might see the DNA of Individual 2’s dad and mom, we’d see that Individual 2 DOES match Individual 1, however is NOT a legitimate match. Individual 3 inherited the primary 5 DNA places from their mom and the second 5 DNA places from their father.

Whereas Individual 2 technically is a match to Individual 1, they aren’t a reputable match as a result of the phase of DNA that matches doesn’t descend from the identical dad or mum. Which means that the DNA didn’t descend in a single piece from ONE ancestor, however clearly descended in items from two ancestors – one maternal and one paternal.

Due to this fact a technical match that isn’t a genealogical match as a result of the DNA is inherited partly from each dad and mom is called a false constructive and is alleged to be Equivalent by Likelihood, or IBC. You’ll be able to read about IBC matches here.

False Unfavourable Matches

A false unfavorable match is simply the alternative. False negatives happen when two individuals are NOT reported on one another’s match lists once they truly would match if the entire DNA on the varied required places have been examined, learn and reported precisely. In different phrases, if imputation weren’t needed.

  • False negatives may be attributable to imputation not working as precisely as we’d hope. Imputation is a likelihood software, and it’s not excellent.
  • False negatives can be attributable to differing match thresholds at completely different distributors.

For instance, if one vendor experiences matches at 6 cM and above, and a second vendor experiences matches at 8 cM and above, the identical two individuals who match at 7 cM will match on the first vendor, however not on the second.

The one approach you’d ever learn about a false unfavorable match, as a result of they aren’t reported, if in the event you merely occur to match at a vendor who permits smaller thresholds.

Additionally, remember the fact that every vendor creates their very own imputations algorithms, so two completely different distributors utilizing imputation on the identical file could produce completely different outcomes.

Figuring out Legitimate Matches

So, how would possibly you establish which matches are literally legitimate matches?

That’s an incredible query.

There are helpful “hints:”

  • In case your dad and mom have examined, a legitimate match will match one among your dad and mom on that very same phase of DNA. In case your match does NOT match one among your dad and mom, it’s a false constructive match and invalid for family tree.
  • If solely one among your dad and mom has examined, and your match does NOT match the examined dad or mum, you may’t presume that individual mechanically matches your different, non-tested dad or mum. That match might match your non-tested dad or mum, or may very well be IBC.
  • If neither of your dad and mom have examined, examine to see in case your match additionally matches shut relations who’ve examined, however not your descendants. For instance, if a match additionally matches your aunt or uncle, or first cousins, that will increase the likelihood that the match might be legitimate.
  • The bigger the match, the extra doubtless it’s to be a legitimate match. For instance, matches within the 6-7 cM stage are IBC about half the time. By the point you’re evaluating matches on the 20 cM stage for a single phase, they’re correct nearly on a regular basis.

Remember the fact that every matching phase have to be confirmed individually, and never each vendor shares the places of the segments that match.

So What Is a Match?

  • A match is an individual who’s discovered in your match listing at one of many main distributors.
  • A match at one vendor is probably not in your match listing in the event you each have DNA at one other frequent vendor resulting from varied causes together with the seller’s match standards, imputation or file compatibility points.
  • A match could also be false constructive, or IBC which isn’t an correct match for family tree. That is very true for smaller phase matches.
  • A false constructive match can happen due to inaccurate reads, imputation or as a result of your match is equivalent by probability.
  • The bigger an identical phase of DNA, the extra doubtless it’s to be an correct match which means you and your match share a standard ancestor.
  • One of the simplest ways to inform in case your match is legitimate is to match your match to each of your dad and mom as nicely.

A match is just not a assure that you just share a standard ancestor except you might be matching to shut relations. You gained’t match a detailed relative if the match is just not legitimate.

What About You?

What’s your plan to confirm that your matches are legitimate?

Have your dad and mom examined their DNA? Both of each dad and mom?

If that’s the case, ask on your dad and mom to add their DNA with you to every vendor the place you add your individual outcomes.

At every vendor, you’ll have completely different matches. That’s precisely why we fish in a number of ponds.

I at all times work with my closest matches first, as a result of I’m the more than likely to have the ability to simply determine our frequent ancestor.

Find your closest identified relations from each your mom’s facet and your father’s facet at every vendor. These individuals will probably be extraordinarily useful for our subsequent article about shared matches.



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