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Genetic Testing Guide

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Denis Law
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 all 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:

  1. 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 (your XX or XY chromosome)—to build a better picture of your genetic ancestry and ethnic composition.
  2. Mitochondrial DNA (mtDNA) – This test scans your mitochondrial DNA, which is inherited directly from your mother. These tests can trace your ancestry through your maternal lineage (your mother’s family tree) dozens of generations back to give you a great idea of your heritage and can help you discover aspects such as migration patterns, interesting ancestries, and more. Both men and women can take this test.
  3. Y-DNA – As opposed to your mitochondrial DNA (the X chromosome), 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 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 atoms that make up each bit of your DNA, which are chained together into a double helix (a sort of twisted ladder)—that act 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.

Y-DNA

When testing kits mention your “Y-DNA”, what they are referring 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 is your “sex chromosome”—the one usually described by an XX or XY. Women inherit two X chromosomes, 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. Your Y chromosome contains the information about your paternal lineage (your father’s line) back through hundreds and even thousands of years. More importantly, your Y-DNA can be used to provide supporting evidence of a biological relation, although it is limited by only providing a part of your ancestry picture.

X-DNA

The other half of the sex chromosome is the X chromosome (sometimes referred to as X-DNA). Much like Y-DNA your X-DNA contains the genetic information passed down by your biological mother and her mother before that. This is an important way to determine your ancestry, to prove a blood relation, and to understand where your family and your identity come from. Generally, X-DNA tests are more often used in conjunction with other tests, as they only give you a partial look at your ancestry (your mother’s side), and can be more useful for people with a Y chromosome, as the X chromosome almost always comes from a biological mother.

What is Autosomal DNA Testing?

Unlike X-DNA and Y-DNA tests, which focus exclusively on your sex chromosome, an autosomal DNA test (or atDNA) looks at the other 22 pairs known as autosomes. These tests can provide a much broader picture of your ancestry, since they are scanning DNA that is shared from both your biological father and mother. This means that when labs sequence your genotype, they can compare it with a massive database of other DNA samples and give you a more comprehensive view of your ancestry, your ethnic composition, and in some cases even your family’s migration history dating back up to six generations. If you’re simply seeking to learn more about your ancestry and build your family tree, an atDNA test may represent your optimal choice.