Xcode Life And 23andme Ancestry: Admixture Calculation

A common aspect of a typical genetic ancestry report is understanding the population labels that match your DNA. This is expressed as a percentage value as many of you may have seen in your 23andme ancestry reports. When a report shows a relatively high percentage composition for a specific population then it is common to assume that you may have a recent ancestor from that population. A quick look at how companies come to these conclusions can help in understanding these results.

Ancestry testing companies use admixture mapping method for gene mapping. Different companies have a different technique. Companies like Xcode Life focus on South Asian ancestry while 23andme ancestry is mostly for the European population. While most companies rely on admixture, some have proprietary algorithms that utilize machine learning for their analysis.

23andme ancestry analysis method

23andme ancestry genetic testing uses a proprietary algorithm that determines your most recent ancestral location (within the last 3-5 generations). Following are some of the highlights of the 23andme ancestry analysis method:

• Their classification tool considers markers that match the majority of the references that are labeled for the whole segment ignoring the markers that form a smaller proportion of the segment.
• Using a smoothing technique (described in detail here –http://www.eurasiandna.com/2017/02/07/23andmes/), 23andme further reduces the minor admixture. Smoothing involves removing the minor population markers that appear intermittently along the length of a segment with many of the major population markers.
• When this method is used, genetic inputs that are older than around 500 years ago are hidden.
• However, in their reports, it is common to see someone from Iran being assigned 98% Middle Eastern and person from Pakistan getting a 98% South Asian even though both of them have a common ancestor dating not too long ago in the past.
• The main reason for this is that companies like 23andme and AncestryDNA focus on recent genealogical time frames.

Xcode’s ancestry analysis method

• Xcode’s method of ancestry analysis is different from 23andme’s method. Also, refer to an earlier blog that details the population labels that Xcode uses.
• We do not employ the smoothing algorithm. This means we do not ignore the minor admixtures just because they are eclipsed by the major admixtures in a segment.
• Hence our reports give ancestry information way beyond 500 years.
• The reports are based on publicly available databases that have been accumulated from studies published in peer-reviewed journals. It is constantly updated to keep up with the latest findings.
• Expanding the list of ethnic groups under each population is on the roadmap.

It is extremely important that you understand the reference populations used in the classification, how population labels were determined, and what classification algorithm was used to determine your ancestry reports.