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Mutation rates
A mutation is not a common event, but the rate at which markers mutate, as you may know, is the subject of variance and debate. Some of the difficulties are:
1) Each marker has a different individual mutation rate. Some mutate slowly, some fast, and some at a medium rate.
2) Individual marker mutation rates vary from family to family
3) Individual marker mutation rates vary between Haplotypes (wide groupings of individuals of the same ancestral origin)
4) Different testing companies include different markers in their tests. For example there are a larger number of fast mutating markers in the FTDNA 37 marker test, than the Genebase 44 marker test. Thus the average mutation rate of FTDNA's 37 marker test (approx 0.0041, or 0.41%) is higher than the average mutation rate of Genebase's 44 marker test (approx 0.0027, or 0.27%)
5) Some studies have small sample sizes and this does not always provide reliable data
How do we cut through this to arrive at values for marker mutations that are meaningful?
There are tens of thousands of test results and more being added all the time. The good news is that studies are revealing mutation rates which are broadly consistent. For example, a slow mutating marker may have a variance between different studies, but it will still be a slow mutating marker. By the same token a fast mutating marker in one study does not suddenly become a slow mutating marker in another, it still remains a fast marker across different tests.
We have taken results for individual markers from as many sources as possible, from wide private studies to published testing company data, and then for each individual marker taken the average of all sources. So for each marker we have a specific mutation rate which is based on a massive amount of data (some 75-100,000 results). See our mutation rate database. With such a database, the calculation of the most common recent ancestor becomes much more reliable. In fact, using our data we conducted an analysis of our predicted TMRCA, and compared it to the actual TMRCA where this was known. In 75% of cases, our prediction of the TMRCA was accurate.
The database is constantly being refined, but at the moment, the Genebase 44 marker test has an average mutation rate of approx 0.0027, or 0.27%, and the 67 marker test, approx 0.0041, or 0.41%. If you use a different company than Genebase, then you can still use the data for each marker and using your company’s specific markers, overlay this data and calculate an average mutation rate for your particular test