DNA (Deoxyribonucleic acid)

Have you ever wondered what makes a daisy a daisy and not a dandelion. Or why you have your dad’s curly hair or your mom’s brown eyes. The answer is a secret, a tiny instruction book hidden deep inside every living thing, from the tallest redwood tree to the smallest buzzing bee. I am that instruction book. I am the recipe that tells a kitten how to grow whiskers and a caterpillar when to build its chrysalis. I look like a super-long, twisting ladder, a spiral staircase so tiny you would need a powerful microscope to see me. The rungs of my ladder are made of special pairs of letters that form a secret code. This code contains every single detail for building and running a living thing. That includes you. I hold the recipe that tells your body how to grow, what color your hair should be, and even whether you can roll your tongue. I am the blueprint for you. People call me DNA, which is much shorter and easier to say than my full name, Deoxyribonucleic acid.

For thousands of years, I was one of the world's biggest mysteries. Humans knew that children looked like their parents, but they had no idea how those instructions were passed along. I was invisible, hiding in plain sight inside every cell. Then, on a chilly day in 1869, a Swiss scientist named Friedrich Miescher was studying cells from bandages when he noticed something new. He found a substance he had never seen before and called it 'nuclein'. He didn't know it then, but he was the very first person to see me. He had found the instruction book, but he didn't know how to read it. Decades passed, and more scientists began to study me. By the 1940s, they had proved that I was the one carrying all of life's instructions, but they still had a giant puzzle to solve: what did I look like. My shape was the key to understanding how I worked. The biggest clue came from a brilliant chemist named Rosalind Franklin. In the early 1950s, she used a special X-ray machine to take a picture of me. Her most famous picture, which she called 'Photo 51', was a bit blurry, but it clearly showed that I was a spiral. Another scientist, Maurice Wilkins, showed her photo to two other scientists, James Watson and Francis Crick. When they saw that X-shaped pattern in the photo, they knew they were close to solving the puzzle. Using her picture as their guide, they built models out of metal and wire until they finally got it right. On April 25th, 1953, they announced to the world that they had discovered my secret shape. I was a 'double helix', a beautiful and perfect twisting ladder.

Once scientists understood my double helix shape, it was like they had found the key to a secret library. They learned how to read the letter-pairs on my rungs, and this changed the world forever. Can you imagine all the amazing things I help people do now. I help doctors understand why some people get sick and how to create medicines to make them better. I help detectives solve crimes by matching tiny, invisible pieces of me left behind at a crime scene to the person who was there. I'm a time traveler, too. Scientists can study me in the bones of animals that lived thousands of years ago, like giant woolly mammoths, to learn what they were like. One of the biggest projects ever was called the Human Genome Project. For years, scientists from all over the world worked together to read the entire human instruction book for the very first time, finishing their map in 2003. Now, they can look at my code to find the recipes for all sorts of things. I am the thread that connects you to your parents, your grandparents, and all of your ancestors. I connect you to every living thing on the planet. I am the story of life, and you are a unique and wonderful part of it.