Tuesday, November 22, 2011

The Simple Way to Understand Genetic Genealogy Tests, Part 2

In part one of this series we discussed mitochondrial DNA and how it mutates (changes) so slowly that there are almost no changes over genealogical time periods, which would be the last 700 years when surnames and vital records have been commonly maintained.

However, the y-chromosome does mutate much more frequently. In fact if you are looking at 67 markers on the y-chromosome, the mutation rate is about 100 times the rate of mutation of the mitochondrial DNA.

If you wish to think of these markers as a hand of cards, about one changes in each four times the cards are dealt. However, an easier way to visualize these changes is to imagine a slot machine with 67 wheels turning, not the three wheels on the machine illustrated. Only about every 4 times you pulled the lever would you get a change in one wheel—corresponding to a marker on the y-chromosome. You would be pretty much guaranteed a change with 9 pulls of the lever.

Not only that, the change would be such that it could easily be seen as the offspring of the original!

For this reason, y-DNA testing is the most widely used genetic test for genealogy purposes. We know that males carry their father’s same y-chromosome, with the occasional one-mutation change.

This property of the y-chromosome allows us to see which men are related to each other within a genealogical time frame and how closely they are likely related along their paternal line. It is of great use to establish lines of descent when records are not available that accurately trace the movements and offspring of our ancestors. However, it requires a sample from a male, and samples (and hopefully genealogies) from other men who turn out to be related.

Lalia Wilson for the Taylor surname project

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