The Long Road to the Scissors: A Century of Gene Editing Prelude

The Brno August heat pressed down on the monastery walls like a damp wool blanket, the scent of ripening peas and thyme curling through the stone corridors. Gregor Mendel, a 33-year-old Augustinian abbot with round wire-rimmed glasses perpetually sliding down his nose, knelt in the dirt between the rows of his experimental plants, his fingers stained green from pod sap. For eight years, he had planted 28,000 pea plants, cross-pollinating them by hand with a tiny paintbrush, counting every round and wrinkled seed, every yellow and green pod, every tall and short vine. No one in Brno, not even the other monks, understood what he was doing. To them, he was just the quiet abbot who spent more time in the garden than in the pulpit, the man who had once failed the teaching certification exam because he could not control a rowdy classroom of village children.

On a gray afternoon in 1865, he stood at the podium of the Brno Natural Research Society’s meeting room, reading a paper titled “Experiments on Plant Hybridization” to a room of 40 farmers, teachers, and amateur naturalists. He explained how the traits of pea plants did not blend, as most people believed, but separated cleanly across generations: a cross between a yellow-pod plant and a green-pod plant did not produce yellowish-green pods, but only yellow or green, in a precise 3:1 ratio. The audience murmured politely, then left to discuss the price of wheat and the latest church gossip. Mendel’s paper was published in the society’s obscure local journal, sent to leading botanists across Europe, and almost universally ignored. The great German botanist Karl Wilhelm von Nägeli wrote back to say his data were too perfect to be real, surely the product of wishful thinking rather than careful counting. Disheartened, Mendel abandoned his pea experiments, turned to administrative work as abbot, and died in 1884, buried in the monastery cemetery with no marker noting his role as the father of genetics. His paper would sit unread for 35 years, until three European botanists working independently—Hugo de Vries, Carl Correns, and Erich von Tschermak—stumbled on it, replicated his experiments, and finally gave his laws of inheritance the recognition they deserved. By then, the man who had first mapped the rules of heredity was long gone, his pea seeds burned in a monastery fire decades after his death.

The delay in recognizing Mendel’s work was not a failure of observation, but a failure of context: 19th-century biology had no framework for discrete, particulate units of inheritance, no language for the idea that traits were carried by invisible, unchanging entities passed from parent to offspring. The same would prove true for the next 80 years of genetic research: every step toward understanding the molecular basis of heredity was taken in the dark, by scientists who could not see the final shape of the puzzle they were assembling. The first piece of that puzzle would not fall into place until 1944, when a gruff, unassuming Canadian-American bacteriologist named Oswald Avery stepped onto a stage at the Cold Spring Harbor Laboratory and announced that he had proven DNA, not protein, was the molecule of heredity.

Avery’s proof came from a simple, brutal experiment with pneumonia-causing bacteria. The smooth, virulent strain of *Streptococcus pneumoniae* had a polysaccharide capsule that let it evade the immune system; the rough, non-virulent strain lacked this capsule, and could not cause disease. When Avery and his colleagues Colin MacLeod and Maclyn McCarty ground up smooth strain bacteria, extracted their molecular components, and added each component separately to cultures of the rough strain, only the DNA extract turned the harmless rough bacteria into deadly smooth ones. The result was undeniable: DNA alone carried the information to build the capsule, the trait that determined whether the bacteria would live or die. But the scientific establishment refused to believe it. Proteins were complex, made of 20 different amino acids, and clearly capable of carrying information; DNA was a simple molecule of just four repeating nucleotides, a “stupid molecule” as the prominent protein chemist Alfred Mirsky called it, incapable of holding the complexity of life. Avery, a man who hated the spotlight and rarely spoke at conferences, was vilified in scientific meetings, dismissed as a sloppy experimentalist who had failed to eliminate protein contamination from his DNA extracts. He would die in 1955, never seeing his discovery win the Nobel Prize it deserved, his colleagues recalling that he spent the last years of his career alone in his lab, repeating his experiment over and over, as if trying to convince himself he had not made a mistake. “I almost began to believe those who said I was wrong,” he wrote in a letter to his brother in 1945, “until I saw the result for the third time, and knew I could not have been wrong.”

The proof that would silence the critics came not from a bacteriologist, but from a 23-year-old graduate student named Rosalind Franklin, working in a lab at King’s College London. Using X-ray crystallography, a technique that bounces X-rays off the regular, repeating structure of molecules to produce a diffraction pattern that can be decoded into a 3D structure, Franklin produced the sharpest image of DNA ever captured: Photograph 51, a fuzzy cross-shaped pattern that proved DNA was a double helix, with the two strands running in opposite directions. Franklin was a meticulous, uncompromising scientist who refused to share her data with her lab mate Maurice Wilkins, and who had no interest in the race to decode DNA’s structure being waged by an American postdoc named James Watson and a British physicist named Francis Crick. But without her permission, Wilkins showed Photograph 51 to Watson and Crick in early 1953. Within weeks, Watson and Crick built their famous double helix model, with the two sugar-phosphate backbones on the outside and the four nucleotide bases (adenine, thymine, guanine, cytosine) paired in the middle, A always with T, G always with C, a perfect zipper that could both store information and replicate itself. On April 25, 1953, their one-page paper was published in *Nature*, alongside papers from Franklin and Wilkins that provided the experimental proof for the structure. Franklin would die of ovarian cancer in 1958, four years before Watson, Crick, and Wilkins won the 1962 Nobel Prize for the discovery, her contribution erased from the official narrative for decades.

The night their paper was published, Watson and Crick walked to the Eagle pub in Cambridge, ordered pints of bitter, and clinked glasses. “We have found the secret of life,” Crick announced, to the amusement of the other patrons. It was a boast, but not an empty one: the double helix was not just a pretty structure, it was a blueprint. If genes were made of DNA, and DNA was a sequence of four bases that encoded the instructions for building every protein in every living thing, then in theory, if you could read that sequence, you could rewrite it. The 20 years after the double helix discovery were a frenzy of decoding that code: in 1961, François Jacob and Jacques Monod discovered the first gene regulatory element, the lac operon, proving that genes were not just static blueprints, but were turned on and off by specific DNA sequences. In 1966, Marshall Nirenberg and Heinrich Matthaei cracked the genetic code, proving that every three consecutive DNA bases (a codon) corresponded to one of the 20 amino acids that make up proteins. By 1970, biologists had a complete dictionary of the genetic code, and the first tool to cut DNA: the restriction enzyme.

Hamilton Smith and his graduate student Kent Wilcox discovered the first restriction enzyme, HindII, in 1970, while studying the bacteria *Haemophilus influenzae*. Smith noticed that when he added DNA from a different strain of bacteria to *H. influenzae* cultures,