Guide to DNA Testing

By: Laura Ryan, PhD
Last Updated: July 27, 2018

We live in a fascinating time. Huge leaps forward in our understanding of how our genes function and continual advances in technology combine to make it easier than ever to gain unprecedented insights into our health, ethnicity and family history. According to an MIT study, the number of people who have taken DNA tests doubled last year to nearly 12 million people. And with prices dropping, we expect this number to continue to increase rapidly.

Illustrating various facets of DNA testing

Considering taking a direct-to-consumer test for yourself or a family member? The purpose of this guide is to:

  1. Give you a general understanding of what you can learn from DNA tests.
  2. Explain to you how DNA tests work.
  3. Show you some of your options you have for choosing a test provider.

And lastly, if you are looking for quick expert advice on which test is best for you, don’t worry—we did the research for you! If your interest is ancestry, we’ll tell you how to choose the best DNA ancestry test. Visit our separate health testing guide if your goal is to find the best DNA test for health.

On this page:

So what exactly can you learn from DNA tests?

Ethnicity estimates

Helps answer: Who am I and where did my ancestors come from?

By analyzing your DNA and comparing it with those of various regional sample groups from around the world, DNA tests can give you broad estimates of where your ancestors likely came from. Different companies can provide different levels of location accuracy, depending on how extensive their databases are, and how sophisticated their analysis is. For instance, here is a picture of my ethnicity estimates from AncestryDNA.

screenshot of ethnicity estimates from AncestryDNA

Ethnicity testing can provide highly accurate results on a continental level, and also on certain historically smaller and more genetically isolated groups, such as Native Americans or Ashkenazi Jews. However on a more local level the results become harder to decipher, as the free movement of people within continents has obscured differences between populations. For instance, it is easy to pinpoint a relatively small percentage of East African DNA in a European individual’s genome, but less simple to assign the majority of the DNA to a specific European country, such as France, Italy or Germany. While this ambiguity can be frustrating, location accuracy is constantly improving as more data is gathered by the service providers, and companies such as AncestryDNA now claim to be able to assign your origins to over 350 distinct regions around the world!

Genealogy

Helps answer: Who are my specific ancestors and living relatives?

DNA tests can help you identify relatives you never knew you had. The major testing companies have proprietary ‘relative-finding’ tools to help you. And DNA testing can help you identify recent and long-ago ancestors in your family tree. You may be surprised how far back into the past this can take you, especially if you find living relatives who are doing the same kinds of ancestry research! To learn more, visit our guide to DNA ancestry testing.

Health risks, wellness, and carrier status

Helps answer: Do I (or my children) face higher risks for certain diseases or other ailments?

By comparing your DNA with genetic markers detailed in scientific research and literature, certain DNA tests can help predict your risks of developing various health ailments, such as breast cancer, age-related macular degeneration, or Parkinson’s disease. Testing for health risk factors can provide truly invaluable information that may help you make better medical decisions or allow you to take preventative measures, but reports must also be interpreted with care, and it is wise to consider the implications of good or bad results before taking this kind of test.

Some companies such as 23andMe offer an additional service called a “Wellness report”. This report contains information that doesn’t indicate specific genetic conditions, but can help you understand how likely you are to experience deep sleep, your predisposition for addiction, your natural genetic weight, or your proclivity for lactose intolerance. This information can help to guide you in terms of your diet and lifestyle, but is also just really interesting and fun to review!

“Carrier status reports” are a little different, as they tell you if you are carrying certain genetic variant that usually does not affect your health, but could affect the health of your children. If both parents are carriers of a disease-causing variant, for instance a variant causing cystic fibrosis, there is a 1/4 chance that each of their children will inherit the disease. A word of caution—the information in these reports often needs to be taken with a grain of salt. But, nevertheless, it is helpful in giving you a heads up that you may want to consult a geneticist for certain high risks for serious ailments.

Visit our guide to DNA health testing in order to learn more.

Other traits

Helps answer: Am I likely to have fast twitch or slow twitch muscles? How sensitive am I likely to be from caffeine?

Satisfy your curiosity! “Traits reports,” such as the popular one by 23andMe, are more fun in nature and are created both by consulting scientific literature, and by determining how selected genetic markers that you have correlate with others who have taken the test and answered lengthy survey questions. For example, I personally have always sneezed after being exposed to direct sunlight when coming from a dark indoors room. It turns out that I have a relatively common genetic condition called photic sneeze reflex—yes, this is a true phenomenon. My son also has this and it is no longer a mystery. Other fun traits you can learn about include chin dimples, taste preferences, and even asparagus odor detection!

How do DNA tests work?

DNA and genes and chromosomes, oh my!

DNA, genes and chromosomes diagram

DNA in Eukaryote Cell by Magnus Manske, licensed under CC 3.0

Our bodies are made up of trillions of cells, the basic units of life. Within the nucleus and mitochondria of each cell there is genetic material called DNA (deoxyribonucleic acid), that controls almost every aspect of how a cell functions. DNA is often referred to as the “blueprint” of life, because as cells multiply, their DNA is the informational code that directs the development of new cells (similar to how building blueprints direct the construction of new buildings). Specific areas of DNA molecules contain sequences of code that determine traits that are passed down from parent to offspring, and these are called genes.

Chromosomes are long strands of DNA that contain many genes. With rare exceptions, humans have 46 chromosomes arranged in 23 pairs, where one chromosome from each pair is inherited from your mother, and the other from your father—this is where the testing company 23andMe gets its name. Hopefully our diagram illustrates how all these terms fit together.

DNA double helix and bases

DNA is a double-stranded molecule in the shape of a double-helix composed of a sugar-phosphate backbone, onto which are attached four different bases: adenine, thymine, cytosine, and guanine. The sugar and phosphate form the supporting DNA strands (shown in grey) and the bases form the inside pairs (shown in color). How the four bases are arranged spells out the language known as the genetic code, which determines who we are. Most genes can be thought of as recipes for making specific proteins. These recipes are replicated and passed down from parent to child, generation after generation.

The copying of the recipes, however, is not always perfect. Sometimes copy errors are made, and these errors are called mutations. Some mutations are harmful, and can cause severe disease, but many are neutral and contribute to the natural genetic variation we find between individuals. If such a mutation is passed down through the generations, and becomes prevalent to a certain degree in a population, it becomes known as a single nucleotide polymorphism (SNP, pronounced: “snip”). Of the over 3 billion base pairs in the human genome, around 10 million are SNPs. Essentially, this means that we share over 99.5% of our DNA; the 0.5% difference caused by accumulations of SNPs accounts for most of the variation between you and everyone else on the planet. Amazing!

As SNPs are heritable and vary between populations, comparing the SNPs that pop up frequently in one group of people vs another is how we can make educated guesses about where your ancestors came from, and what physical traits you are likely to have. DNA testing is simply the process of extracting your genetic code, focusing on what SNPs are present in your code, and telling you what traits, ethnicity, or disease risks are currently thought to be associated with those particular markers.

The DNA collection process

Submitting your DNA to a DNA test provider such as 23andMe or AncestryDNA is incredibly simple. You just have to submit your saliva or a swab from your cheek and the lab does the rest. The first step in the extraction process at the lab is to isolate the DNA so that it is in a purer form. Then, the DNA is placed into a machine where it is analyzed by a DNA genotyping chip. These chips target specific genetic markers, usually short DNA sequences surrounding SNPs. Once the sample is genotyped, the information is loaded into the data system and you are sent a report outlining what your DNA says about you.

Different types of DNA

One last thing that is helpful to understand is that the DNA in our bodies can be grouped into several different categories. We will cover here the three most common categories used for direct-to-consumer (DTC) DNA testing.

Autosomal DNA

We mentioned earlier that almost all humans have 23 pairs of chromosomes in the nucleus of most of their cells. Of these 23 pairs, 22 of them are made up of what we call Autosomal DNA. This means that the DNA contained on these 22 pairs of chromosomes is not integral to determining the sex of the individual. One copy of each of these chromosomes is inherited from one’s father and the other from one’s mother.

Why take this test and what are the limitations? Autosomal DNA forms the basis for most of the information we can learn from genetic testing, as it covers 22 of our 23 chromosome pairs, and can provide information about traits, ethnicity, ancestry and disease susceptibility/wellness. Autosomal DNA is inherited from both parents, and both men and women can have their autosomal DNA tested. Many genetic testing service providers focus solely on testing autosomal DNA, and it is by far the most common type of DNA analysis.

Y-chromosomal DNA (or Y-DNA/yDNA)

The “23rd pair of chromosomes” is unlike the other 22, and is often referred to as the sex chromosome pair. This pair determines whether you are genetically male or female. In almost all cases, a person inherits an ‘X’ chromosome from their mother, and either an ‘X’ or a ‘Y’ from their father (there are rare genetic disorders where we see other combinations). If your sex chromosomes are ‘XX’, you are genetically female, while if they are ‘XY’, you are male. Since only males have a Y-chromosome, this chromosome and its associated y-DNA is exclusively passed on from father to son.

Why take this test and what are the limitations? Y-chromosomal DNA testing is only available to men (as women do not have a Y-chromosome), and can allow male customers to gain great insight into the genetic ancestry of their father. Y-DNA is particularly useful for ancestral genetic testing because it does not undergo a rearranging process called recombination, unlike the other chromosomes, which are reshuffled and rearranged between each generation.

Women: do not despair! If a close male relative such as your father, brother, paternal uncle, or paternal male cousin were to have his genome tested, you can predict your own paternal lineage results from his reports.

Mitochondrial DNA (mtDNA)

illustration of mtDNA

Mitochondrial DNA is very unusual, as it comes not from the cell’s nucleus, but rather the cell’s energy-producing “factories” called the mitochondria. mtDNA is circular in shape and is only passed down from mother to child. Male children carry their mother’s mtDNA, but they do not pass it on to their children, who instead inherit it from their mother.

Why take this test and what are the limitations? Mitochondrial DNA makes up a tiny proportion of the human genome and does not tell you about traits you are likely to have, as it’s purpose is solely to govern the function of the cells’ energy producing centers. However it can still provide information regarding ancestry, and is particularly useful for this purpose. As mtDNA is inherited exclusively from your mother, and like yDNA does not undergo recombination, analysis of mtDNA allows genetic scientists to trace your maternal lineage back through potentially hundreds of generations. Both males and females can take mtDNA tests, but only to investigate the ancestry of their mother.

If you’re interested in learning more about mtDNA, take a look at reports concerning the widely publicized “3-parent baby” born in 2016, and at the concept of the “mitochondrial eve”.

Short summaries of the major DNA test providers

We directly review and give detailed comparisons of the major test providers HERE, but here’s a quick introduction to them all:

  Family Tree DNA AncestryDNA 23andMe MyHeritage LivingDNA TeloYears
Price See latest See latest See latest See latest See latest See latest
Our Overall Rating
Autosomal
Health Testing    
   
yDNA
 
 
 
mtDNA
 
 
 
Approx. Database Size 1 million 7 million 2 million 700K   Unknown
Accepts Data from Elsewhere
   
 
Genealogical Community
   

The "Big 3"

AncestryDNA

AncestryDNA is an offshoot of A ncestry.com, which has long been a destination for genealogy and family tree building. Your DNA test results can help you greatly in those genealogical pursuits, as can Ancestry.com’s huge community and database.

23andMe

Who says you can’t have it all? Not 23andMe, where you can learn about your ancestry and health with one test package. 23andMe offers all three types of direct-to-consumer test (autosomal, yDNA and mtDNA).

Family Tree DNA

Family Tree DNA is one of the oldest providers in the business, and their reputation among serious genetic genealogists is sterling. They provide a wide array of DNA tests at different prices for the purposes of learning all about your ancestry.

Other providers to consider

TeloYears

Like 23andMe, TeloYears offers DNA testing for both health and genealogical purposes. But TeloYears’ approach to health-related DNA testing is unique, focusing on telomeres—a particular component of your DNA—to give you information about how well you are aging and subsequently how vulnerable you are to developing age-related disease.

MyHeritage DNA

Like Ancestry.com, MyHeritage has been a go-to site for genealogists for quite some time, and more recently began offering DNA testing. They also deliver their results quickly!

LivingDNA

Are you pretty sure you’ve got ancestry from the British Isles? Are you a little Irish on days other than St. Patrick’s Day? LivingDNA’s ancestry testing delivers British Isles ancestry details with great micro-regional detail.

Third party databases

Third party databases are not testing companies, but rather places where you can upload your DNA testing data in order to connect with even more potential relatives and people whose research can help you with your own.

GEDMatch

The GEDMatch database continues to grow at breakneck pace. You may have heard about it recently as the database that helped California revive a cold case and catch the Golden State Killer.

Promethease

A health-focused reporting system that accepts data from any of the “Big Three” companies above. Using SNPedia (a wiki database of SNPs), Promethease offers to show you some of the health-related DNA information that other companies don’t show you.

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