#Only 30% of my dna matches my father full#
For example, between 200 cM and 340 cM, the most probable relationship is Group E, but the full range for that group is 65–600 cM (see below). Note that the numbered ranges to the right of the graph mark regions where that group is the most likely one, not the full range for that group. Figure 5.2 from the AncestryDNA Matching White Paper edited to use the groups defined by the DNA Detectives chart. Here’s what the modified figure looks like.
To make the information easier to understand, I edited the image labels to use the groups from the DNA Detectives chart. They also misuse the word “meioses”, confusing people who aren’t familiar with the term as well as those who are.
Unfortunately, they used a logarithmic scale, which is a great space saver but is intuitive to precisely no one.
This graph was taken from the AncestryDNA Matching White Paper published 31 March 2016 (their Figure 5.2). Distributions of shared centimorgans for different relationship categories based on simulated data. Their graph is based on simulated data, rather than empirical (real) data, but as long as the model they used to do the simulations is reasonable, the data should be reliable. AncestryDNA’s Matching White Paper (31 March 2016) presents an informative graph (their Figure 5.2) that shows the likelihood of each group (the x axis) given the amount of shared DNA (the y axis). When you have a match in an overlap zone, the best approach is to consider the most likely group first. Someone who shares 1315 cM with you can only fall into Groups B or C, but someone who shares 100 cM could belong to Group E, F, or G, according to the DNA Detectives chart. Worse, the more distantly related the group, the broader the range of shared centimorgans relative to the average and the more overlap there is with other groups. Put another way, someone who shares 1315 cM with you could be in either group (and remember that each group includes multiple possible relationships). Notice another problem? The low end of the Group B range overlaps the high end of the Group C range. Group C can range from 575 cM to 1330 cM. That is, someone in Group B might share 1750 cM with you, but they could also share as little as 1300 cM or as much as 2300 cM, according to the DNA Detectives chart. To complicate matters, each group is defined not so much by an average or “expected” amount of shared DNA but by a range. The original chart is available in the files of the DNA Detectives Facebook group. Shared centimorgan ranges for different relationship groups. I will use the DNA Detectives group names in the rest of this post for ease of reference. In the two examples above, grandparent/child, aunt/uncle, and half sibling would be Group B, and great-grandparent/grandchild, first cousin, great-uncle/aunt/nephew/niece, or half-uncle/aunt/nephew/niece would be Group C. The DNA Detectives Facebook team has designed a nifty chart that categorizes relationships into groups based on the expected amounts of shared DNA. (In this case, you can narrow the possibilities using age.) Someone sharing 950 cM with you could be a great-grandparent/grandchild, first cousin, great-uncle/aunt/nephew/niece, or half-uncle/aunt/nephew/niece. Those relationships are indistinguishable based solely on the amount of shared DNA. For example, a woman who shares 1750 cM with you could be your grandmother, granddaughter, aunt, or half sister. Why not? One reason is that multiple different relationships can give the same patterns of shared DNA. Unfortunately, with the exceptions of identical-twin, parent–child and full-sibling matches, that’s simply not possible. The one thing we genealogists probably want most from our autosomal DNA matches is something they can’t give us: an exact relationship prediction based on shared DNA alone.