Generally, a genealogical DNA test might use either autosomal STRs or autosomal SNPs. However, testing companies do not currently offer autosomal STRs tests that use enough STR markers for genealogy. Some ethnic population matching products use them. The preferred choice for both genealogy and ethnic population matching is microarray chips that use hundreds of thousands of autosomal SNPs.
Like Y-DNA STRs, autosomal STRs are counts of repeated genetic code. As autosomal DNA recombines each generation, the number of markers shared with a specific ancestor is reduced by half each generation.
Like mtDNA and Y-DNA SNPs, autosomal SNPs are changes at a single point in genetic code. Autosomal DNA recombines each generation. Therefore, the number of markers shared with a specific ancestor decreases by half each generation. Most testing companies overcome this by using technologies that include around 700,000 autosomal SNPs.
There are currently two types of matching processes used.
The first is haploblock matching. This process counts the number and size of matching runs of DNA from one point to another. It then computes the likely number of generations between two people.
The second method is biogeographical analysis. This method seeks to match individual SNP values’ frequencies in reference populations to match geographic origins.
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