Personal Genetics: DNA, SNPs, GWAs, and Haplotypes
Ask Science explains the different elements of our genetic make-up. How do they work together to determine our traits? Click to find out.Â
Chances are, you or someone you know has had their genome analyzed by one of the many personal genome testing services. You probably also heard that the FDA recently ordered that one of those companies, 23 and Me, stop providing health reports for those tests due to some issues they had with the way those results were presented.
Whether you think the FDA was right or wrong about this, let’s take a look at what kind of information goes into these tests, and what you can and can’t learn from them.
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DNA 101
As I’ve mentioned on several past episodes, the genetic information you have comes from two sources, your mother and father. For the majority of people, every cell in your body has 23 pairs of chromosomes. One set comes from your mother, and one from your father.
Each of those chromosomes is a very long string of DNA made up of four different types of molecules called nucleotides. Those nucleotides are Guanine, Cytosine, Thymine, and Adenine. Each chromosome has between 40 million and 250 million of these nucleotides.
When we talk about a DNA sequence, what we are usually referring to is a long list of letters that represent that long list of nucleotides. Usually, the nucleotides are abbreviated to G, C, T, and A, respectively.Â
By themselves, these nucleotides don’t really do anything. However they contain the instructions that tell your cell how to build proteins, RNA, and other molecules it needs to keep your body running smoothly.Â
When genetic sequencing was first in its heyday, scientists believed that by looking at your genetic sequence, they would be able to figure out everything about you, from your eye color to your IQ to how likely you were to get a certain disease. Unfortunately, things turned out to be not quite that simple…..
SNPs, GWAS, and Haplotypes, Oh My!
Before we look at some of those issues, though, let’s look at the type of information these personal genetic testing services provide.
First, they don’t give you your entire DNA sequence. Instead, they provide you with a list of SNPs. A SNP (usually pronounced “snip”), which stands for “single nucleotide polymorphism,” is a single location in your DNA which has been shown to be different for different people.Â
For example, at a certain place on chromosome number 16, there is a gene called ABCC11. The proteins encoded by this gene do various things, but scientists discovered that a single nucleotide in this gene dictates whether or not your earwax is wet or dry.Â
This location (given the handy name of “rs17822931”) usually contains either the nucleotide Cytosine (C) or Thymine (T). Now, remember that you have two copies of chromosome 16 – one from mom, and one from dad. If both copies contain Thymine at that location, you get dry earwax. If you have a Cytosine at that location in either copy of chromosome 16, then you belong to the wet earwax club.Â
Now you might be wondering, how on earth did scientists figure that out? Well one way scientists try to associate different SNPs with what they cause is through a technique called a Genome Wide Association Study, or GWAS.Â
In these types of studies, scientists get a big group of individuals and divide them into two groups.: those that have the condition they’re looking for, and those that don’t. Then they look at as many SNPs as they can in each person and try to identify patterns.Â
So if everyone in the dry earwax group has a certain nucleotide at a certain location (scientists say that these people have the same allele,) then scientists can say that the SNP is associated with the condition they are studying.Â
Note that all we can do with a GWAS is associate a SNP with a condition. We can’t say that having the SNP causes the condition, or even that having the SNP makes you more likely to have a condition.Â
One more topic I want to mention briefly today is something called a “haplotype.” A Haplotype is a group of SNPs that tend to always stick together, down through the generations. For example, the dry earwax SNP I mentioned earlier belongs to a haplotype that is common in people of Asian ancestry, particularly Chinese and Korean ancestry.
Conclusion
ConclusionSo now you know more about DNA, SNPs, GWAS, and Haplotypes. Next week, we’ll take a look at what all of this has to do with personal genetic testing.Â
If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.comcreate new email. If you liked today’s episode, you can become a fan of Ask Science on Facebook or follow me on Twitter, where I’m @QDTeinstein.
Photos of male scientist and female scientist courtesy of Shutterstock.
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About the Author
Dr. Lee Falin earned a B.S. in Computer Science from the University of Illinois, then went on to obtain a Ph.D. in Genetics, Bioinformatics, and Computational Biology from Virginia Tech.Â
