Definition
DNA is a long chemical molecule that holds all the information a living thing needs to grow and live. A gene is a meaningful blueprint unit inside that DNA that makes a specific product the body needs, such as a protein or RNA. Traits like blood type are shaped by the action of genes like these.
A Giant Library and One Cookbook Inside It
Picture a library with thick books lined up as far as you can see. All the long paper tape stored on its shelves is the giant substance called DNA. Inside every cell in your body, a strand of DNA is packed in, tightly twisted. It is too thin to see, but stretched out it would be about 2 meters long.
But the whole tape is not used at once. One part of the tape holds a recipe for making a specific part, like "how to make insulin." Another part holds "how to make a protein that helps blood clot." A stretch of DNA that holds meaningful information for making a protein or RNA is what we call a "gene."
So DNA is the name of the material itself, like the paper or tape with writing on it. A gene is a unit of information, like a meaningful story or recipe written on that paper. Like a library and a single book, the two point to different things.
A Code of Life Written in Just Four Letters
A computer stores every photo and video using just two digits, 0 and 1. In the same way, living things record all their life information with just four chemicals. These four letters are called adenine (A), thymine (T), guanine (G), and cytosine (C), the four kinds of bases.
The order in which these four letters line up completely decides the shape and use of the protein that gets made. For example, three letters together pick out one amino acid (a basic building block of proteins). These blocks link up in a long chain to make your muscles, skin, and digestive enzymes.
Amazingly, it's not just people. The dandelion by the road, the squirrel in the forest, and even bacteria too small to see all keep life going with the same four-letter chemical code.
A Little More Precisely
It's easy to think "DNA is all protein blueprints." But in human DNA, the stretches that directly carry protein information make up only about 1 to 2 percent (around 1.5 percent). Even inside a gene, there are stretches with no protein information (introns). Some genes make only RNA. Most of the rest does not make proteins directly.
In the past, this remaining part was sometimes called useless junk. But as science advanced, we learned that some of it works as a precise control system, switching genes on and off to decide when and how much they work. Still, how much of it truly has a function is still debated.
Also, having the same genes does not mean living exactly the same way. Depending on what you eat and the environment you live in, which gene switches are on or off can change. The field that studies this is called epigenetics.
Common misconceptions
DNA and genes are exactly the same word.
DNA is the chemical that holds life information (the whole long thread). A gene is a functional stretch of information within that thread that makes a protein or RNA.
100% of human DNA is filled with protein blueprints.
Only about 1 to 2% (around 1.5%) of all DNA directly carries protein information. Some of the rest does jobs like controlling how genes work.
Where you meet it
Identical twins look alike because they split from a single fertilized egg and share DNA with nearly the same base sequence.
Like the DNA stretches that hold the recipe for the enzyme making melanin, the pigment behind hair color, a single trait can involve several genes working together.
In one sentence
DNA is a long chemical ladder that holds all of life's information, and a gene is a meaningful recipe inside that ladder for making a specific protein.