How to read what your DNA says about your body, your past, and your people
Have you ever been curious about those DNA tests that promise to tell you where your ancestors came from or what health risks you might carry? I was. I spit in a tube, mailed it off, and a few weeks later—boom—pages and pages of data.
It said my ancestors’ originated in different parts of Europe and Asia, and it showed me about 1,500 cousins who I never heard of. Then there was all this extra stuff about genetics. Cool… but also confusing. I didn’t know what I was really looking at. What’s a G:G? What’s a SNP? What even is a gene?
So, I decided to dig deeper. This is the first post in a series where I break down what I learned about genetics —starting from the absolute basics. I took Biology and Anatomy classes, and studied a lot on the internet. But I forget, easily, so this is also a refresher for me, too.
The “Big Book of You“
Think of your DNA like a giant, detailed book—the book of you. Maybe we don’t think about it too much, but books are structured in specific ways to allow us to understand the information inside. The book is made up of individual letters, grouped into words; which are grouped into sentences; and they are grouped together in chapters — a hierarchy of pieces of information that make sense when they all go together.
So, DNA has the equivalent of 4 letters (ATGC), and words (triplets), sentences (genes), chapters (chromosomes), and the whole book (DNA). And just like a book, tiny changes in the letters arrangement can make a big difference in the meaning—or maybe no difference at all.
DNA was kind of discovered as early as the 1860s, but it was only in the 1950s that the important double-helix structure was understood. And it wasn’t until 2001 that the first human genome was mapped and published. We’ve come a long way since then, the cost of testing has come down a lot, and we now know a lot about what DNA does, and how it is mapped out. But we do not know everything, a lot more to discover. The mystery of life is an ongoing field of study. And we can all be part of it at this point.
So What Is DNA, Really?
DNA stands for deoxyribonucleic acid (yeah, big word—but don’t worry, you don’t have to memorize it). It’s the molecule that carries the instructions for building and running your body. Every cell in your body (except red blood cells) has a full copy of this same instruction manual inside of it. The DNA is located in the nucleus of the cell — nuclear DNA.
There’s a second kind of DNA inside cells that most people don’t know about — inside important structures called mitochondria. These are small biological machines that convert fuel into energy. You inherit your mitochondria from your mother’s egg.
Nuclear DNA and mitochondrial DNA together are called the human genome, the library of humanity.
How Can I Read What Is Inside My DNA?
DNA is made up of four basic “letters,” and these letters that scientists use are stand-ins for small molecules called nucleotides. You know this already, but molecules are groups of atoms, the smallest bits of chemicals, arranged in specific ways. Like hydrogen and oxygen combine to make water, and sodium and chloride combine to make salt. These special or chained together into strands of DNA.
- A (adenine)
- T (thymine)
- G (guanine)
- C (cytosine)
If you ever saw or heard of a sci-fi movie named “GATTACA,” that title is a play off of these letter sequences. It’s an interesting film, about class differences created between people of natural human births vs. people who are designed with “genetic perfection.” A very real ethical dilemma to think about as the future comes zooming at us.
Nucleotides pair up in a special way: an A always pairs with a T, and a G always pairs with a C — like AT or TA, or GC or CG. These nucleotides are then ordered into chains, one next to the other, to form two long strands of letters that contain a kind of coding, like a programming language. The strands of DNA will naturally twist into a shape called a double helix. Think of it as a like a really long ladder, if you twisted it counter clockwise over and over, with the pairs of letters as the rungs, and a sugar-phosphate “backbone” as the side rails that hold everything together. 🧬
Nucleotides on their own aren’t very meaningful—they’re like letters without words. But when they’re grouped into sets of three—like ATC, GGA, or CTC—they form the basic “words” of the genetic code. These triplets are called codons when they’re copied into a usable form.
That usable form is called RNA—a working copy of the DNA used to build proteins. One small difference: RNA uses the letter U (uracil) instead of T (thymine). There are good biological reasons for this—some having to do with chemistry and stability—but I also like to think it helps keep RNA and DNA from getting mixed up.
From DNA to Genes to You
DNA is broken up into 23 different parts, like chapters of a book — 22 body chromosomes (autosomes) and 1 sex chromosome (allosomes). This is where the genetics company called 23AndMe got its name. Actually, you have 23 pairs of chromosomes — one full set of instructions from your mother, and another full set from your father. This is important to know, and we’ll come back to this in a minute. But all together, it takes about 6.4 billion individual nucleotides to explain how to make a human being. All living animals, plants and microbes on Earth have DNA, but the number of chromosomes and nucleotides differs significantly. For comparison, dogs have 39 pairs and cats have 19 pairs of chromosomes, compared to people’s 23.
Within each chromosome are individual genes—shorter sequences that tell your body how to make proteins. Proteins are molecules that do most of the heavy lifting in your body, providing structure and performing tasks. They build muscles, digest food, fight infections, and so much more. You’ve got about 20,000 to 25,000 genes, spread out across your 23 pairs of chromosomes.
But here’s the kicker: Most of your DNA isn’t made of genes. In fact, only about 1–2% is! The rest plays other roles we’re still learning about—like regulation, timing, and structure.
Is DNA a Protein?
Nope. DNA is DNA — a type of molecule, not a protein. It does carry the instructions for making proteins. Think of DNA as the recipe, and proteins as the product of the recipe.
What’s an SNP, and Why Should I Care?
When I got my DNA test back, I got to the scientific section, and saw it had a database of mysterious entries, like “rs123456: G/G” and I had no idea what it meant. Turns out, this is an example of an SNP (pronounced “snip”), short for Single Nucleotide Polymorphism.
An SNP is a specific spot in the DNA chain where humans often have a tiny variation in one letter. Maybe most people have an A there, but you might have a G instead. These little changes gives humanity variety and make us each a unique person — with some genes being linked to traits like eye color, or health conditions like diabetes.
Every SNP sits at a specific locus (location) on a chromosome—kind of like saying, “Look on page 3, paragraph 2, word 5 of the Book of You.”
What Causes Variations Between People?
Ah, this is where the inheritance and pairs of DNA from each parent are important.
When your body is making sex cells — either a egg in a woman or a sperm in a man, it is creating a package that contains DNA to make the next generation. But the package only contains half of what is required — it needs the other half to start the baby constructing process.
What is interesting about egg and sperm creation is that a special process called called recombination happens. This is where parts of your two different sets of DNA are randomly mixed together to create a new set of DNA. For example, a man’s sperm may contain more instructions about his father’s eyes, and his mother’s nose. That’s a simplification, but the point is that the sperm receives one full set of information and instructions to carry to the egg, but it is a nearly random mixture of the father and mother. Which is why full siblings will look a bit different in height or hair, and other characteristics that might affect health, metabolism or even personality.
The sperm set is called a paternal haploid, and the egg set is the maternal haploid. Together, the form a new diploid genome. Only in maternal twins or triplets, for example, will siblings be the same diploid.
However, as a person lives, and they are exposed to various different environmental factors over the years — ie. infections, toxins, nutrients, radiation — there will be small genetic changes happening to a person. So then, no two people are ever exactly alike, even if you cloned them, the way gene expression and mutations happen is left to inevitable circumstance.
Am I a Mutant?
Yes—technically, you are. But don’t picture the X-Men just yet. In biology, a mutation simply means a change in your DNA sequence. And every human being carries dozens—if not hundreds—of these changes compared to the reference human genome.
Some of these mutations were inherited from your parents. Others may have appeared in your body for the first time—de novo mutations, which can happen during the formation of sperm or egg cells, or even as your cells divide over time. These changes can come from a variety of sources, including:
- Errors in DNA replication (your cells copy DNA billions of times throughout life)
- Environmental exposures (like UV rays from sunlight, cigarette smoke, or pollution)
- Chemical processes inside your body (normal metabolism can generate reactive molecules that damage DNA)
What kinds of mutations are we talking about?
There are several types:
- Point mutations – a single letter in the DNA sequence is swapped for another (like changing a word in a sentence)
- Insertions and deletions (indels) – one or more letters are added or removed
- Copy number variants – chunks of DNA are duplicated or deleted entirely
- Structural variants – large sections are rearranged, flipped, or even moved to other chromosomes
Most mutations don’t do much. They may land in parts of the genome that aren’t involved in making proteins or regulating genes. Some do influence traits—like whether you can digest milk as an adult, how you process certain medications, or whether your hair curls. And a few mutations can cause disease—but these are usually rare or require a combination of other genetic and environmental factors.
So, should I worry?
Probably not. Mutation is part of life. It’s what fuels evolution, diversity, and even innovation in nature. Without it, there would be no new traits, no adaptation to changing environments—and no humans at all.
Even identical twins—who start out with nearly identical DNA—will accumulate different mutations as they age. Each cell in your body even carries a slightly different set of mutations, thanks to the natural process of cell division. That means your liver cells might not be genetically identical to your skin cells.
So yes, you’re a mutant. But so is everyone else. It’s not a flaw—it’s part of what makes you unique.
What Is “Gene Expression”?
If your DNA is the instruction manual for building and running your body, then gene expression is the process of actually using those instructions.
Think of each gene as a recipe in a massive cookbook. Gene expression is like deciding which recipes to cook, when to cook them, and how much of each dish to make.
Not every gene is turned “on” all the time in every cell. Your cells choose which genes to express based on their cell type, functional purpose, environment, and what the body needs at the moment. This is what allows your eye cells to behave differently from your liver cells—even though they all carry the same DNA.
How does it work?
- Transcription
First, the cell copies the DNA instructions for a gene into a temporary message called RNA. This step is like copying a recipe onto a notepad so you don’t spill tomato sauce on your big fancy cookbook. - Translation
Next, the RNA is used to build a protein—a molecule that does real work in your body. Proteins can form structures (like hair or muscle), carry signals (like hormones), speed up reactions (like enzymes), or protect you (like antibodies).
Together, transcription and translation are the two main steps of gene expression.
Why does it matter?
Gene expression helps explain why:
- Identical twins can look or act slightly different
Even with identical DNA, their gene expression patterns may diverge over time due to life experiences, environment, and randomness. - You might carry a disease-causing mutation and never get sick
If a gene isn’t being expressed in the tissue where the problem would happen, the mutation might not have any noticeable effect. - Drugs work differently for different people
Genes involved in breaking down medications may be expressed at higher or lower levels depending on your DNA and environment. - Traits can change over time
Some genes switch on during puberty. Others may quiet down with age, stress, or lifestyle changes. Your gene expression shifts with you.
Normally, all of this works pretty well, but sometimes it goes horribly wrong. Children can be born with genetic defects that cause disease. Cells can become cancerous. Allergies can come and go. Autoimmune disorders can become permanently damaging. Endocrine organs can send out hormonal signals that affect mood, thoughts, appearance, and metabolic function.
So, researchers are looking for ways to control gene expression—not just to prevent disease, but possibly to enhance human health and function. Maybe you’ve heard of CRISPR and Cas9, two powerful tools that can potentially edit genetic code and regulate gene activity.
At the same time, marketers are also pushing products you may have come across—like nutritional supplements or probiotics—that claim to “hack” your gene expression. Most of these are ineffective or not scientifically sound, so it’s important to stay critical and consider the source. This is an exciting field with remarkable breakthroughs, but also full of big promises and questionable conclusions.
My own knowledge is still a work in progress, and I thank you for reading. I hope you found this interesting—and I’ll be back soon with a look at genetic testing and what it can reveal about who we are.
