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.
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. On the Family Tree DNA pages, RSRS haplogroup names are displayed.
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