The CRS and the RSRS

Before we talk about the new Reconstructed Sapiens Reference Sequence, RSRS, let’s talk for a minute about the current comparison model, the Cambridge Reference Sequence, also known as the CRS or rCRS.

When analyzing mitochondrial DNA, your results are compared to the results of an anonymous individual whose DNA was sequenced in 1981 at Cambridge University.  This set of results which has become the standard is called the Cambridge Reference Sequence, or CRS.  Everyone else’s DNA is compared against theirs, and the differences (mutations) duly noted.

What this means is that for comparison purposes, the current state of their mitochondrial DNA in 1980 is considered “normal” and any differences are then considered “mutations.”

All DNA testing companies as well as academia use this model, but this is changing.  Enter, the RSRS.  What is the RSRS?

The Reconstructed Sapiens Reference Sequence or RSRS

In April, 2012, a groundbreaking, watershed, paper was published by Dr. Doron Behar and 8 other authors titled “A “Copernican” Reassessment of the Human Mitochondrial DNA Tree from its Root.”

You can read the paper and download the supplementary data at this link:  http://www.cell.com/AJHG/abstract/S0002-9297(12)00146-2

Previous to this new paper, mitochondrial DNA results have always been reported by comparing your mtDNA to the Cambridge Reference Sequence.  This has been problematic for a number of reasons, but let’s just look at one example.

Mutation 16519C is present in just about everyone.  In fact, in more than half of the people.  So what this really means is that it’s not really a mutation in the people who carry 16519C, it really was a mutation in the anonymous person who is the Cambridge Reference Sequence.  But since they did not carry 16519C, it’s reported as a mutation in the rest of us.  However, it’s really the “normal” state of the DNA, or what we call the ancestral state.  And it’s relatively useless when comparing your results to others because nearly everyone has it.

What Dr. Behar has spent years doing is going back in time, genetically, and reconstructing what we believe the original “mitochondrial Eve” looked like, at least in terms of her mitochondrial DNA.  He could do that because he took the time to sort through each haplogroup, taking him back in time to the ancestral state of all of the mutations, in other words, before they happened.

The result is something called the Reconstructed Sapiens Reference Sequence, or RSRS.

Why does this matter to you?

Today, when people at other companies are still using the older CRS, it doesn’t matter much, but it will in time as other companies adopt the new model too. It means that your reported mutations change. The RSRS is much more accurate and allows for a uniform naming of the various haplogroups from an ancestral base.  Your haplogroup name may and probably will change between the two.  Today, they are still the same on your personal page at Family Tree DNA, but in the future, they won’t be.

There may be a time during the transition where you’ll need to know if you’re using CRS or RSRS numbers.  Fortunately, for Family Tree DNA clients, you’re being provided with both, so you’ll be able to use either one or switch back and forth, as needed.

Haplogroup Name Changes

Whether or not the new reference sequence becomes widely accepted or not, this project by Dr. Behar has very successfully found many new subgroups of haplogroups.  In some cases, the haplogroups got shuffled a bit as to where their branch lives on the tree, based on new discoveries.  In my case, I have a new letter appended to my former haplogroup name, J1c2 to J1c2f, but for others, the change is significant.  Today, on the Family Tree DNA pages, the haplogroup names remain the same, but the updated names will be added in the future.

mtDNA Community

If you can’t wait (I couldn’t) to find about your haplogroup name changes, you can follow the instructions on the mtDNA Community tab.  We will talk about the mtDNA Community in a future blog.

34 thoughts on “The CRS and the RSRS

  1. Roberta, I hope you cover the mtDNA Community tab as soon as possible. I want to understand it before I upload anything to it including security, etc.

      • The mtDNA Community tab is missing on both of my mtDNA results. There also is no added explanation on the help page for the RSRS results.

      • The My Community tab is only available for people who took the full sequence test. Did you? Also, I discovered that there is no additional help for the RSRS page. For now, it sends you to the My Community site. I’m sure Family Tree DNA will add to their FAQ library soon. However, this is one reason I blogged about it.

  2. On my results I have the Revised Cambridge Reference Sequence for the HVRI and HVRS. My haplogroup is the same. Should it change?

  3. I noticed the “Private Mutations” listed in the papers submitted that defined a haplogroup. Will these private mutations eventually be used to define subclades? If so, how many submissions must be submitted before a subclade is defined?

    • That is a great question Larry. The old rule used to be three unrelated (as in not known to be related) matches constituted a subclade, but I think now that there are so many more full sequences, that rule either has or will need to change. Part of it depends on whee the mutations land on the tree branches. In other words, to some extent, it depends of “when” the mutation occured. Sometimes parallel mutations do actually occur in completely diffeent lines. The insertion mutations at locations 309 and 315 are a great example of that. I think now they are looking more for groups of mutations rather than single location mutations to define haplogroup branches.

  4. Roberta thanks for your response. I did not take the Full Sequence test, I only tested HVR1 and HVR2 so that explains the missing tab.

    By the way, I did find the article you referenced – ‘A “Copernican” Reassessment of the Human Mitochondrial DNA Tree from its Root’ informative.

  5. Roberta, I transfered my data to the site by mtDNA HVR1 and HVR2 and haplogroup sequence gave L2a1c1 Ftdna complete the transfer became L2a1c1a is normal this happen?

  6. Hello Roberta! Changing the mtDNA haplogroup change the ethnicity of a person or remains as before the change there? Mean when he was L2a1c1 the history of this haplogroup remains the same after the change?

    • The history of the haplogroup remains the same. What will change is the twig on the branch of the tree. Of course, you know now that I said that, there will be at least one exception:)

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    • The CRS and the RSRS are two different ways of looking at the same data. The Copernican is one of the words in the paper that I referenced that provides dates for haplogroup births. One of us is confused:) Maybe both.

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  12. If the CRS standard did not have a mutation on “its” DNA that everyone else has then I am assuming that this “anonymous” individual from the CRS is from a very old human sample in whom the mutation had not yet arisen?

    • It was a sample of a living person in 1980. If you’re referring to 16519C, it’s actually the opposite. That person did have a mutation at that location, but since it’s the reference for the rest of us now, it looks like we all had that mutation, when we don’t. The RSRS resolves that problem.

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