Saturday, October 4, 2014

Understanding genetic testing for genealogy

Since I majored in genetics in university and my one true passion is family history, you'd think I'd be all over genetic testing for genealogy purposes. But I'm not. I actually had to look at this article on Wikipedia to figure out what kinds of tests they run. But let's start at the beginning. DNA.

Basic genetics

1. All of your cells contain your DNA.
2. Each cell has DNA that is organized into 46 different strings called chromosomes.
3. There are only 23 different types of chromosomes, so you have two copies of each type of chromosome.
Depiction of a chromosome, organized DNA
4. Genes are sections of the string of DNA that send signals to the cell. The order (sequence) of the DNA building blocks determines the signals sent.
5. Most of the DNA is not genes. These "extra" sections are more likely to vary from person to person.
6. New DNA mutations that can be passed down through generations are rare, but do happen over time.
7. Half of your chromosomes come from one parent, half from the other.
8. Some of the chromosomes that your parent gave you came from one of your grandparents and the rest came from the other grandparent (not necessarily half and half, though).
9. The Y chromosome can only be passed from father to son. X chromosomes can be passed down from either parent.
10. Mitochondrial DNA is separate from your main DNA and can only be passed from mother to child.

Applications for genealogy 

Close up depiction of DNA 
Your genetic information comes from your ancestors. All human DNA is 99.9% the same, but there are lots of places where that 0.01% could differ. If you can compare your DNA to someone else's, the similarities and differences should allow you to guess how closely you are related. 

There are certain locations on the DNA strands where mutations (changes) are known to have occurred. (Basically, we know where some of that 0.01% is.) It would take much too long to look at all of the DNA, so we can see if two people are related by testing how similar their DNA is at some of these known locations. 

This kind of testing has been going on for some time in the form of paternity testing. Genetic testing for genealogy is like a paternity test that compares your DNA to a list of potential cousins instead of a list of potential fathers.

Types of tests

There are three broad types of genetic tests for genealogy.

1. Testing the DNA in the normal (autosomal) chromosomes. This test includes DNA from both of your parents. You can't tell which of the results come from which side of your family, but hopefully you would be able to contact some of your potential cousins and work together to find out. This is the most comprehensive kind of test because it includes DNA from almost all of your chromosomes, so even though the results may be confusing, they are probably the most accurate.

2. Testing the Y chromosome. This test includes DNA passed from father to son only, so your father's father's father's etc. line.This test is great because you know precisely which of your ancestors it applies to, but there are only a few known locations to test on the Y chromosome, so the results are not very comprehensive. (If you are a girl, you have to get a male in your family to take the test for you because you don't have a Y chromosome).

3. Testing the mitochondrial DNA. This test includes DNA passed from mother to child only, so your mother's mother's mother's etc. line. As with the Y chromosome test, the results are precise but not comprehensive.

Close up depiction of DNA

The quality of the test depends on two main factors:

1. How many and which of the known locations are tested. 

There are lots of known locations to test and even more that we don't know about. The lab will probably only choose a few locations to test in order to keep costs down. They don't have the ability to test locations that they don't know about.

2. How many people the test is compared to.

You may not have much information about the people they are comparing you to. Genetic genealogy is only as valuable as the other people who take the test. In fact, the first person to take the test gets no value from it until they can be compared to someone else.


Will genetic testing replace records-based genealogical research? Nope. They're not comparing you to a bunch of potential ancestors that you can just add to your tree (though that is possible if you can find DNA from a potential ancestor); they're comparing you to a bunch of potential cousins who are currently alive. You still have to find the ancestors yourself, though you may have some valuable help from your new-found cousins. You may also find out that you have roots somewhere you never thought to look. You're not going to get any names or stories about your ancestors back from the lab.

So is it worth it? I don't know. It depends on what you're looking for and how stuck you are. I don't think I'd do it because I usually find lots of available records on my ancestors. If I didn't have any information on my genealogy at all or if I were super rich, maybe. Genetic testing for genealogy is a cool idea, but I think it sounds more interesting than useful.

Would you be interested in genetic testing?

Photocredits: cooldesign, dream design, and Victor Habbick

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