Sardinia Signature

PCA Based Ethnic Origins – Part 6, Genealogical markers

It is day six, and we are back to genealogy. The only thing that is going to change PCA ethnic origins into a meaningful product for genealogists and even for personal ancestry enthusiasts is to use markers that date to the genealogical and historic time frames.

Microarray chip based tests like they sell at Ancestry, 23andMe, and Living DNA are samples of our genomes tested with known variants. Most of those variants are common to at least 5% of the human population around the world. Some are selected to be between 1% and 5% of the human population. That means they have been around for a long time.

  • No private variants.
  • No family variants.
  • No genealogy variants.
  • No historic time-frame variants.
  • Very few Bronze Age variants.

The variants on a microarray chip date to the first farmers who spread agriculture 10,000 years ago, to the Out-of-Africa travellers 50,000 to 70,000 years ago, and even back to early stone age ancestors who predated modern humans. On most microarray chips, some medical variants (mutations) are included. These are often the youngest markers on the chip.

If we want to find if we have ancestry from the British Isles with great certainty, then we need genetic markers that are only found in the British Isles. This is not going to be easy. As most of us know from Y-DNA and mtDNA Haplogroups, the people of the British Isles have been in near continuous movement with wars and migrations since the first settlers arrived there. Maybe we need a more realistic goal.

If we are going to determine if someone’s genetic ancestry is consistent with origins in the British Isles in the past 250, 500, and 1000 years, then we need markers that art 250, 500, and 1000 years old. If we are going to use SNPs, then we need to use the results from Whole Genome tests. Those can be personal or from public data-sets (1K Genomes etc.).

That is a lot of testing. Up front, it sounds expensive. Yet, testing much like it is how we as genetic genealogists created the mtDNA and Y-DNA trees we have today.

Are there other ways? Perhaps. Perhaps, it is time for us to stop determining ethnic origins using PCA. Perhaps, it is time for us to use segment matching, autosomal STRs, or something else?

In the next few posts, I will go over each of those, and some common misconceptions about ethnic origins testing.

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