Ignore the precision (to 2 decimal places). I showed that because I wanted to highlight the nonzero African ancestry percentage which I will talk about in more detail some other day.
The ancestry painting also shows you the segments on your chromosomes and which ancestral group you inherited them from. Here’s an image showing mine:
Does this mean I am 91% European and 9% Asian? Not quite! My results are about typical for someone from Punjab.
Also, the results depend on which reference populations were used as the exemplar European, Asian and African populations.
23andMe takes advantage of publicly available data for four populations studied extensively via the International HapMap project (hapmap.org). That project obtained the genotypes for 60 individuals of western European descent from Utah, 60 western African individuals from Nigeria, and 90 eastern Asian individuals, 45 from each of Japan and China. Because the two eastern Asian populations are geographically near one another and relatively similar at the genetic level, 23andMe combines these to form a single eastern Asian reference population. For more information on why these regions were used, please see (Why are these three populations used?)
So they are comparing your DNA segments to those of the three populations from the HapMap dataset. Using more reference populations would give you more fine-grained results (which is something I plan to do in my Harappa Ancestry Project).
Using the technique described by Eurogenes, you can check which chromosomal segments are classified as European (C), Asian (A) or African (Y). Here are my results for chromosome 9:
The number of Asian segments on my homozygous chromosome 9 makes me doubt that it comes from my Egyptian great-grandmother. May be it’s from my great-grandfather.
The African segments are on chromosome 8:
I need to do ancestry painting on my own in more detail.