Before you order a DNA Test or whole-genome analysis, you should probably beef up on some of those biology terms you have long forgotten. But worry not! This guide will lead you through all the terms you need to understand when getting the results from a direct-to-consumer genetic home test.
First Things First, What is DNA?
DNA is shorthand for deoxyribonucleic acid. This molecule holds all of the information your cells need to survive and reproduce. DNA is stored as chromosomes, and humans have 23 unique chromosomes. Each of these chromosomes contains the information necessary to produce various proteins, which work together in immensely complex networks to form a functioning body.
On each chromosome, there are multiple genes. Each gene is made of small molecules called nucleotides. There are only 4 different nucleotides used: adenine (A), guanine (G), taurine (T), and cytosine (C). The cell’s machinery reads these nucleotides in groups of three, called a codon. Each codon signals a different command to the cell’s machinery, including commands for “STOP”, “START”, and commands for each piece of the protein.
The codons together contain a replica of the base structure of a protein. Proteins are made up of many individual amino acids, which form together like a chain to make a functioning protein. There are only 21 amino acids, and the DNA nucleotide codons can call for each one specifically. These completed protein molecules then fold into unique shapes, and have a variety of functions. Some proteins copy DNA, some hold cells together, and some are enzymes, which allow the cell to control chemical reactions.
All together the genes on your chromosomes are referred to as your genome. Your genome encodes all of the proteins in your body, which in turn allow your cells to operate, grow, and reproduce. Though the process is much more complicated than this simple description, this is easy to remember. DNA makes protein, proteins complete cellular tasks.
When someone gets their DNA tested, scientists are actually reading the genetic code, down to the nucleotide sequence. Though there are only 23 unique chromosomes, you get one copy of each chromosome from each parent. This gives you two copies of each gene. This is important, because each copy can have minor variation. These different versions of the gene are known as alleles. These alleles form slightly different shapes of the proteins being created, which can result in differences in function. By learning which alleles you carry, you can learn about how your genetics may affect your health and livelihood.
How Can Scientists Read DNA?
To read your DNA, the laboratory will first need a sample. To get a DNA sample, most labs request a simple cheek swab. To do this, you simply drag a cotton swab across the inside of your cheek. Your cheek cells will slough off onto the swab, and from those cells, scientist can extract your DNA.
The cheek cells are washed off the swab, and go through the process of DNA isolation. During this process, the cell membranes are washed away, along with other cellular components. This leaves only DNA molecules behind. To analyze the contents of DNA, scientists must employ the Polymerase Chain Reaction, commonly called PCR.
Polymerase is a special protein which can replicate DNA. Using this protein, scientists can add a little heat and some free nucleotides. This allows polymerase to replicate your DNA. This is important, because only a small amount of DNA was collected from the sample. After many rounds of this process, the laboratory will finally have enough material to start analyzing your DNA.
To do this, they first cut the DNA into small, recognizable chunks. Then, they sort the chunks based on size, weight, and electrical charge. From these properties, they can tell which chromosome the genetic material belongs to, and which genes it contains. Finally, the scientists will use advanced computers to “read” the chunks by identifying the individual nucleotides it contains. From this string of nucleotides, scientists can make some interesting conclusions about your DNA.
Things Scientists Learn by Reading DNA
There are several different areas which might be analyzed by a DNA test. Primarily, testing companies are trying to identify which alleles of each gene you actually carry. This is mainly done on autosomal chromosomes. These chromosomes, different from your sex chromosomes, carry the majority of information your body needs. The laboratory will analyze these genes to determine which alleles you carry, and the diseases and character traits those alleles might lead to.
When scientists analyze the Y-chromosome (Y-DNA) of males or the mitochondrial DNA (MtDNA) of females, they are analyzing your relatedness to ancestral groups. The male Y-chromosome is passed from father to son, and goes largely unchanged over time. Likewise, DNA found in the mitochondria (a small energy-producing organelle within cells) passes from mother to offspring relatively unchanged over time. By comparing your DNA in these segments to others, the laboratory can identify which ancestral populations of humans your ancestors belonged to.
Regardless of whether scientists are looking at autosomal or sex chromosomes, they are looking for the same small things. Within the human population, each gene is composed in basically the same form. However, as time drags on and the DNA is replicated and copied, it can start to accumulate mutations. Most of the time, these mutations are small single nucleotide polymorphisms (SNPs). This simply means that in the chain of many nucleotides, a single nucleotide is replaced with another.
These small genetic variations allow scientists to categorize and track DNA through time, as well as identify certain alleles without reading and translating the entire genetic code. Scientists can identify the SNPs within your DNA, and can identify which alleles you are carrying based on the SNPs present. Sometimes, the SNP will not alter the function of the end protein. These are known as silent mutations. Other times, the new nucleotide will accidently end the protein short, known as a nonsense mutation. The mutation can also be mostly innocuous, changing the protein only slightly. This is known as a missense mutation. By understanding the normal gene, scientists can anticipate how these mutations may affect the function of your proteins.
Similar to these small genetic markers are short tandem repeats (STRs). Unlike SNPs, these short repeats contain many nucleotides, but serve as unique markers within the DNA. STRs are commonly used in criminal DNA tests, as unique markers to identify a person by. The FBI, for instance, uses a person’s unique nucleotide sequence in 13 different areas to identify a person with almost perfect accuracy. These short repeats can also be used to identify various alleles or genetic conditions.
The laboratory will assemble all of these things, and build a working picture of your DNA. Their report should give you insights into which alleles you carry, and how your particular DNA sequences may affect your health.
Things You Might Learn from a DNA Test
There are many important things you might learn from a DNA test. First and foremost is a term known as carrier status. Some genetic diseases, such as cystic fibrosis, only afflict patients when that person has two copies of the disease-linked gene. In some cases, people can live normal lives while still carrying around one copy of the malfunctioning gene. These people don’t have the disease, but are known as carriers. Doing a genetic test will likely inform you of your carrier status for several genetic diseases.
In a similar line, many genes offer a resistance to certain diseases, based on the actions of the protein their produce. For instance, sickle-cell anemia is genetic disease, but it also stops the growth of the organisms which cause Malaria. Laboratories can now test for several genes that are known to have relationships with various disease.
The report from your genetic test will likely contain a variety of other genetically influence traits, and the specific alleles you carry. The ability to taste a certain bitter chemical is one example. With certain alleles, you can taste the chemical. With other alleles, you cannot. Similarly, your report might show you alleles pertaining to lactose digestion (the sugar within milk) and caffeine metabolism. These traits biochemical reactions which are influenced in part by your genetics.
Further, your blood type is determined genetically. Your blood type is actually a series of protein which attach to the surface of blood cells, allowing your body to recognize them. By reading your DNA, the laboratory will be able to give you an advanced look at exactly which proteins are being produced.
Lastly, information from your sex chromosomes can determine many things about your ancestry. They may test your maternal or paternal haplotype. A haplotype is a genetic identity shared by large groups of people. Ancestry tests compare your DNA to the DNA profiles of the earliest humans, as they migrated from Africa. Because Y-chromosomes and mitochondrial DNA go relatively unchanged over time, the laboratory can identify roughly when your ancestors migrated from Africa, all the way to around 200,000 years ago. They can also identify if your ancestors interbred with Neanderthals, an extinct but separate species.
Now, What Do You Do With This Information?
Knowing your genetics is only one small step to complete health. You may receive some potentially devastating news. Maybe you have a gene which increases your risk of cancer. But don’t freak out yet.
More important than your genetics alone is a concept called epigenetics. Your epigenetics are your genetics, plus in the environment you put them in. This is extremely important, more so than your genetics alone.
As an example, let’s follow two people on their journey through life. Let’s say that as babies Marcy has a gene that increases her risk of breast cancer, while Ted does not. Given only this information, it is easy to say that Marcy has a higher risk of breast cancer. But that is not even the start of the story.
Marcy lived an outstanding life. She ate a whole-foods, plant-based diet and exercised regularly. Ted was not so nice to his body. He smoked a pack of cigarettes almost every day, and regularly ate fried fatty foods. Now, which person is more likely to get cancer? Results from cancer studies would claim Ted has a much higher risk.
You see, regardless of the genes you inherited, a much more important factor is your lifestyle. As a point of fact, the BRCA gene was hailed after it was found as the “genetic cause” of cancer. Yet, as the years have gone by since its discovery, its importance has dwindled. Not only have scientists found other genes that may be associated with breast cancer, they have also found that the BRCA gene is present in less than 20% of breast cancer cases. That means that 80% of the time, the patient did not have the BRCA gene, but still got cancer.
Your epigenetics are therefore a much larger factor in your overall health, compared to your genetics alone. Sometimes, DNA testing companies will refer to Nutrigenetics, a field that looks at your nutrition in respect to your genetics. This can help yield insights into your personal biochemistry which may help you make the healthiest decisions.
Thanks for explaining that testing can give us insight into our DNA sequences and how they may affect our health. My daughter is learning about evolution in school, so I’ve been curious about any advances that may have been made in the study of DNA sequencing and mutations. I’m glad I read your article because it was interesting to learn how testing can be used to gain a complete understanding of an individuals DNA sequencing.