Genetic Testing Guide
DNA testing has become a popular way for families and individuals to learn more about themselves and their history. Today, you can learn a lot about your ancestry by simply ordering a test online and sending it back to obtain quick results.
Genetic tests can help you discover your ancestry and familial origins, and they can even help you understand your health and body by highlighting any genetic conditions you may have a predisposition for.
However, even though genetic testing seems to be the easiest thing to do, the science behind it can be a little confusing to understand, and even overwhelming when you’re trying to determine why you want a test. Before you dive into selecting a test, it’s worth understanding the different types of DNA tests available, what they scan for, and what the results can mean for you.
The Types of DNA Tests Available
Although there are multiple types of DNA tests today, most home testing kits feature three types:
- Autosomal DNA (atDNA) – This is the most common type of DNA test available on the market today, and it is also the broadest. The test scans your autosomes—the 22 chromosome pairs in your DNA that aren’t related to your sex chromosomes ( XX for females or XY for males)—to build a better picture of your genetic ancestry and ethnic composition.
- Mitochondrial DNA (mtDNA) – This test scans your mitochondrial DNA, which is inherited directly from your mother. These tests can trace your ancestry through your direct maternal lineage (your mother’s mother’s mother etc.) dozens of generations back to give you a great idea of your heritage. This type of test can help you discover aspects such as migration patterns, interesting ancestries, and more. Both men and women can take this test.
- Y-DNA – As opposed to your mitochondrial DNA, Y-DNA tests scan your paternal lineage through the Y chromosome. The benefits are similar to mtDNA tests, but the big difference is that Y-DNA tests are only available to males, as women don’t possess a Y chromosome. Even so, you can have a male relative take the test and compare your results to theirs.
Additionally, some companies also offer medical screening tests that can teach you about your genetic health and highlight any conditions or anomalies that may impact future well-being. These tests highlight genetic markers in your genotype that indicate a higher probability of inheriting or even developing certain conditions and illnesses.
However, it’s worth noting that these results are not conclusive proof that you’ll develop any condition you have a predisposition to. Before radically altering your lifestyle and choices, share your results with your physician to better understand what they mean for you.
What is DNA Sequencing?
DNA is made up of millions of nucleotides—small groups of chemicals that make up each bit of your DNA. They are chained together into a double helix (a sort of twisted ladder)—that acts as an instruction book on how to make and maintain your body.
Most of our DNA is largely the same as everyone else’s, but there are enough distinctions and mutations (also known as alleles) to make us unique. However, simply reading the nucleotides in a genome won’t reveal much if you don’t know the order in which they’re positioned. To understand a person’s genotype, tests must first map out their genome in the right sequence.
This process, known as DNA sequencing, examines strands of your genetic code to map out the order of your nucleotide bases (adenine, or “A”; cytosine, or “C”; guanine, or “G”; and Thymine, or “T”). Once sequenced, labs can compare your results with existing samples and their databases to find genetic markers similar to yours which can then tell them more about your ancestry.
When testing kits mention your “Y-DNA”, what they are referring to is the genetic information stored in your Y chromosome. When humans are conceived, they receive 23 base pairs of chromosomes. 22 of these pairs are known as “autosomal” DNA, while the 23rd pair determines your sex.
Women inherit two X chromosomes (one from each parent), while men inherit an X chromosome from their mother and a Y chromosome from their father. This means that women don’t have a Y chromosome, and thus can’t take a Y-DNA test. The Y chromosome contains information about your paternal lineage (your father’s line) back through hundreds and even thousands of years.
More importantly, Y-DNA can be used to provide supporting evidence of a biological relation between men, although it is limited by only providing a part of your ancestry picture.
Unlike the 23 pairs of chromosomes found in the nucleus of our cells, mitochondrial DNA is an entirely different kind of DNA found outside the nucleus. Everyone has mtDNA but only women pass in on to the next generation. When you get a close match to another person on an mtDNA test, you and that person MUST share a common maternal line ancestor.
Unfortunately, mtDNA mutates slowly, so that common ancestor could be recent or may have lived hundreds of years ago before genealogical records. A common use of mtDNA testing is to see if two people share a common female ancestor in their direct maternal lines or not.