Part 3 - Admixture Proportions by Chromosome
Part 1 yet, you should do so first.
Admixture Proportions by Chromosome shows you your admixture proportions as broken down by individual chromosome; or, in other words, what percentages of each chromosome are most commonly found in which populations/ethnicity. This gives you a much more detailed view of where your DNA is most commonly found.
|Admixture proportions (or ethnicity percentages) broken|
down by chromosome
|My Eurogenes K13 results|
At the bottom it says "Number of SNPs eval" - this is just how many of your SNPs were used for the evaluation.
It doesn't show which particular segments each percentage is found on though, but that brings us to the next options.
Part 4 - Chromosome Painting and Reduced Size
Chromosome Painting is a visual representation of your admixture proportions not only by chromosome but by segments of each chromosome. The different colors show which segments of each chromosome were most similar with which populations. When there are overlapping colors on the same segment, it means that segment is found in more than one population. The higher the spike, the stronger the match to that population. So with segments where there are solid blocks of one color are more solidly found in only that population. Above is just a small portion of one of my chromosomes (7, I believe), as an example of the various populations that will show up for any given segment.
|Chromosome painting reduced size|
You may notice in either the full or reduced size that similar populations (though it's more noticeable in full), or neighboring regions, often spike and dip almost in unison with each other. This is because neighboring regions tend to share a lot of DNA and be genetically similar so when you see this, what you're seeing is that these portions of your DNA may be somewhat indistinguishable among two or more groups. This is important in understanding that not all DNA can be narrowed down to the more specific areas or countries that so many people wish it could, not with any reliability. It also illustrates why you might get results in a region that you have no known ancestry in when it neighbors a region you do have ancestry in.
|23andMe's chromosome painting|
As another example, below is also a graphic from 23andMe - it's not a part of your results from this company, it's just showing, in part, how they determine ethnicity. Their example uses the more detailed type of chromosome painting found at Gedmatch, and it is labelled to show the probability of each ancestry on one side with increasing percentages of likelihood. It can be found in their guide article on ancestry composition. Gedmatch's chromosome painting can be read the same way.
Disclaimer: Please note I am not a professional in the genetics industry, and it is difficult to find information particularly on some of the more advanced admixture tools on gedmatch. This is how I have come to understand the results and tools through my own experiences and research, but please, if someone more knowledgeable can correct me if I've misunderstood something, or can fill in some gaps, let me know by commenting below.