Autosomal DNA Q&A

The classification is based on the present-day allele frequencies in groups that have been divided somewhat arbitrarily. There is no guarantee that the frequencies have remained constant, and so this classification system cannot be applied to the past. If and when there are millions of individual autosomal DNA samples from some epoch in the past, it would be possible to draw small, random, representative populations from among the millions and set up a corresponding, somewhat arbitrary scheme of ethnic classification for that past epoch. But not until then.  (Source)

What results might be expected on autosomal testing conducted on two first cousins?

A scientific study, "STR markers for kinship analysis" by S. Wilkening et al. illustrates that its much more difficult "to identify first cousins (third-degree relatives, who share 1/8th of their DNA on the average). If there are only two people tested, 123 markers only get you a 90% chance of detecting a first-cousin relationship. However, the inclusion of more family members helps considerably." (Source)

Can autosomal testing reveal a marker value shared by a large percentage of participants and would that marker value have a likely geographic origin?

If you're referring to the CODIS-type markers, most values can probably be found in most populations, just in differing percentages. You can look up the raw data for sample populations in OmniPop.
     If two people share the same value, it doesn't necessarily mean they inherited it from a common ancestor. CODIS markers mutate at a rate similar to the Y-STR markers, so the two people could be "Identical by State" or IBS. Sharing a SNP is a stronger indication of common ancestry (being "Identical by Descent" or IBD). SNPs have a very low mutation rate, and we sometimes treat them as Unique Event Polymorphisms, mutations that have occurred only once in all of human history (undoubtedly an exaggeration, but still a useful starting point).  (Source)

What is Omnipop?

Omnipop is a publicly accessible database created by Brian Burritt of the San Diego Police Department.  Omnipop contains primarily CODIS markers which are not "selected to be 'Ancestry Informative Markers' they were chosen because they can, in combination, uniquely identify an individual" (Source)

For more info, visit and/or add your atDNA results to:
DNAPrint Log
DNA Tribes Log

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