## Derived vs Ancestral

3

If an SNP is "not derived", then its considered negative and "ancestral". What does "ancestral" mean in this context?

Wouldn't an "ancestral" result be better than a derived result as I assume "ancestral" means inherited and "derived" means calculated or determined by heuristic approaches.

I've not seen those terms used for SNPs. Can you give us a link to a site that is using them? – lkessler – 2017-10-16T01:23:59.120

for IKessler- see https://www.familytreedna.com/learn/y-dna-testing/big-y/big-y/

– pdrh – 2017-10-16T01:52:57.290

Thanks but doesn't answer my question. – pdrh – 2017-10-16T03:17:26.367

2

You need to learn how the SNP values are named and what they mean. The short answer is that the SNP is particular base in the DNA. It has it's own "address" from one of the ends of DNA helix. SNP's value is the aminoacid located in this position. We made so-called reference genome for convenience. It is described as chain of SNPs with strictly fixed value corresponding to one particular common ancestor of all mankind. The selection of this reference genome is relative. When we will have more data we can change the SNPs value in it to correlate with new information and new conditions.

So in this view the "ancestral" term becomes clear. It means that this particular address in DNA contains the same value as in this reference DNA. If one of your ancestors had the mutation the SNP value will be different because the different aminoacid will be found in this place. It is "derived" SNP.

Unfortunately, sometimes very rare event happens: when back-mutation occurs. It means that the SNP changes it state from "derived" to "ancestral" and all your issue will have again the ancestral version. When we build BIG tree of relationships we try to analyze whole dataset to minimize this effect.

The simple answer also can be obtained via the link: http://forums.familytreedna.com/showthread.php?t=34800

Ancestral = unmutated version of an SNP
Derived = mutated version of an SNP


thanks for the lesson. This answer along with the included link explains these confusing terms well. The original nomenclature could have been made much simpler by using "mutated","unmutated ", and "untested". – pdrh – 2017-10-17T12:56:02.813

@pdrh I totally agree with you that the terminology is sometimes very confusing. But we have what we have :-) and we are forced to use existing language :-) – GEORG GAAL – 2017-10-18T06:51:01.290

FTDNA needs to do a better job explaining these terms in their glossary. Elsie did however in the link you provided. Thanks again. – pdrh – 2017-10-19T10:26:06.863