HAWGOOD FAMILY DNA STUDY
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What does DNA testing tell us?
Ancestral DNA testing will tell us whether parties tested are related and will provide the most likely generation gap, or what is known as the TMRCA - time to most recent common ancestor.
How do the results tell us how far apart we are related?
Put simply, if the markers all match then those tested are very closely related. If a marker does not match, this is known as a mutation, and the more mutations that exist, the further apart those being tested.
As a rule of thumb, in the Genebase 44 marker test, there would be on average a mutation on just one of the markers every 250 years for each person tested. In a 67 marker test, there would be on average a mutation every 100 years. For those mathematically minded, the extra 23 markers are faster mutating markers, which proportionally brings down the average time period for a mutation.
Using the number of mutations and the average expected mutation rate, we can calculate the statistically likely generation gap between 2 parties being tested.
A word of caution on the maths - and more on this later. The calculation to the most recent ancestor rests on the average mutation rate and there is a great deal of debate and confusion on this topic. Early studies (Walsh 2001) indicated a rate of 0.0020, or 0.2%, but later studies has shown mutation rates of 0.0040, or 0.4%. Some more recent data indicates rates in excess of 0.5%.
The existence of more recent higher mutation rates is very easy to explain. Walsh studied only slow mutating markers, and the results were valid for these markers. More recent studies have used many more markers than Walsh, and these markers have higher mutation rates, which raises the average. Between testing companies, the average mutation rates will also vary as different markers are tested. Using accurate mutation rates is key as if the wrong ones are used, for example applying Walsh 0.2% rates to what are in fact fast mutating markers, the estimate of the most common recent ancestor will be wildly out.
Ancestral DNA testing will tell us whether parties tested are related and will provide the most likely generation gap, or what is known as the TMRCA -
How do the results tell us how far apart we are related?
Put simply, if the markers all match then those tested are very closely related. If a marker does not match, this is known as a mutation, and the more mutations that exist, the further apart those being tested.
As a rule of thumb, in the Genebase 44 marker test, there would be on average a mutation on just one of the markers every 250 years for each person tested. In a 67 marker test, there would be on average a mutation every 100 years. For those mathematically minded, the extra 23 markers are faster mutating markers, which proportionally brings down the average time period for a mutation.
Using the number of mutations and the average expected mutation rate, we can calculate the statistically likely generation gap between 2 parties being tested.
A word of caution on the maths -
The existence of more recent higher mutation rates is very easy to explain. Walsh studied only slow mutating markers, and the results were valid for these markers. More recent studies have used many more markers than Walsh, and these markers have higher mutation rates, which raises the average. Between testing companies, the average mutation rates will also vary as different markers are tested. Using accurate mutation rates is key as if the wrong ones are used, for example applying Walsh 0.2% rates to what are in fact fast mutating markers, the estimate of the most common recent ancestor will be wildly out.