Introduction

Have you ever wondered what makes you, YOU? 

Every living thing, from tiny bacteria to humans, is built from a special code hidden inside its cells. 

This code is called DNA, and its discovery changed science forever. 

Let’s take a journey to uncover its secrets!

The First Clues – Mendel’s Peas

Before scientists discovered DNA, a monk named Gregor Mendel laid the foundation for our understanding of heredity. Living in the 1800s, Mendel was fascinated by how traits, such as flower color and seed shape, were passed down from one generation to the next.

To investigate this, he conducted carefully controlled experiments with pea plants in the garden of his monastery. 

From these observations, Mendel formulated the laws of inheritance, which explained how traits are passed from parents to offspring in predictable ways.

By crossbreeding plants with different characteristics, he observed that traits followed specific patterns over generations. 

He discovered what we now call dominant and recessive traits, for example, a yellow seed might appear in one generation, disappear in the next, and then reappear in later plants.

Miescher and the Mysterious "Nuclein"

In 1869, a scientist named Friedrich Miescher discovered a strange substance inside white blood cells. He called it nuclein. 

He didn’t know it, but he had just found DNA!

Although he did not understand its role, his discovery laid the foundation for future breakthroughs in molecular biology. It was only later, as scientific techniques advanced, that researchers determined nuclein was primarily composed of DNA—the molecule that serves as the blueprint of life.

In 1944 Oswald Avery and his research team used a bacterium that could cause pneumonia, which came in two forms: a smooth and a rough form, which differs one from the other since the smooth form of the bacterium had a protective coat that made it virulent (disease-causing), while the rough form lacked this coat and was harmless. 

They observed that when they treated the heat-killed smooth bacteria with enzymes that destroyed proteins, the bacteria still transferred their deadly characteristics to the rough bacteria. However, when they used enzymes that destroyed DNA, the transformation didn’t occur. 

The Key Experiment – Avery’s Discovery

Avery and his team concluded that DNA, not proteins, was the molecule responsible for carrying genetic information from one generation to the next. This was the first real proof that DNA carried genetic information, a revelation that would change the course of biology forever.