From Mendel's Peas to CRISPR: A Short History of Genetics

What happened?

The monk was Gregor Mendel, an abbot at a monastery in Brno (in what is now the Czech Republic), who spent roughly seven years, from 1856 to 1863, cross-breeding pea plants in the monastery garden. He tracked simple, visible traits — seed shape, pod color, flower position — across generations, growing an estimated 28,000 to 30,000 plants by hand. Mendel found that traits didn’t blend together the way most naturalists of his era assumed. Instead, they were passed down as discrete units, later called genes, following predictable ratios. Cross a purebred yellow-pea plant with a purebred green-pea plant, and the next generation wasn’t yellow-green — it was yellow, with green reappearing, unblended, a generation later. Mendel published his results in 1866 in the Proceedings of the Natural History Society of Brno, a journal with limited circulation. The paper drew almost no attention and was essentially ignored for the rest of his life.

It stayed ignored until 1900, when Dutch botanist Hugo de Vries, German botanist Carl Correns, and Austrian agronomist Erich von Tschermak-Seysenegg each rediscovered the same patterns in their own breeding experiments — and each, in the course of writing up their findings, stumbled onto Mendel’s decades-old paper already describing them. (A fourth researcher, American wheat breeder William Jasper Spillman, reached similar conclusions around the same time.) Genetics as a formal field was born not from Mendel’s original publication, but from its rediscovery a generation later.

The next leap came in a cramped attic lab at Columbia University nicknamed the “Fly Room.” In January 1910, biologist Thomas Hunt Morgan was breeding thousands of ordinary red-eyed fruit flies (Drosophila melanogaster) when a single white-eyed male appeared among them. Morgan bred it and tracked how the white-eye trait passed to future generations, discovering that it traveled specifically with sex — a signal that genes weren’t abstract accounting units but physical objects, riding along chromosomes inside the cell. That single fly helped anchor the chromosome theory of heredity, for which Morgan won the 1933 Nobel Prize in Physiology or Medicine.

Four decades later, in 1953, James Watson and Francis Crick described the double-helix structure of DNA, the molecule genes are made of, building on X-ray diffraction data produced by Rosalind Franklin and Maurice Wilkins. From there, genetics accelerated fast: scientists learned to read the DNA code (sequencing), then to read an entire human genome. The publicly funded Human Genome Project, launched in 1990, produced an essentially complete sequence of human DNA by April 2003 — two and a half years ahead of its own schedule.

The most recent turn arrived in 2012, when biochemists Jennifer Doudna and Emmanuelle Charpentier described how to repurpose a bacterial immune system called CRISPR-Cas9 into a programmable tool for cutting DNA at a chosen spot — effectively a pair of molecular scissors that could edit a genome on command. They won the 2020 Nobel Prize in Chemistry for it, the first Nobel awarded to an all-woman team.

Why was it strange?

The strangeness isn’t any single event — it’s the rhythm. Twice, the field’s biggest ideas sat unnoticed in plain sight for years before anyone recognized their importance: Mendel’s paper gathered dust for 34 years, and Morgan actually started his fly experiments in 1908 hoping to disprove Mendelian inheritance, not confirm it. He was a skeptic who became convinced only after the evidence — one odd white-eyed fly — forced his hand. Genetics has repeatedly progressed by researchers stumbling onto answers that were, in hindsight, already sitting in a journal, a breeding cage, or a bacterium’s immune system.

What did scientists learn?

Together, these episodes built the modern understanding of heredity in layers: Mendel showed that traits are inherited as discrete units following statistical rules, not blended like paint. Morgan showed those units (genes) have a physical address, on chromosomes inside cells. Watson, Crick, Franklin, and Wilkins showed what the units are made of — a double-stranded molecule that can copy itself. The Human Genome Project showed what a complete set of human genetic instructions actually looks like, base by base. And Doudna and Charpentier showed that a system bacteria evolved to fight off viruses could be redirected to make precise, deliberate edits to that code. Each layer depended on the one before it.

How does it affect us today?

Mendelian ratios still underpin basic genetic counseling and crop breeding. Genome sequencing, radically cheaper since the Human Genome Project, is now routine in cancer diagnosis, prenatal screening, and ancestry testing. CRISPR-based tools are already approved to treat sickle cell disease and are in clinical trials for cancers, inherited blindness, and other genetic conditions — though most therapies remain expensive, narrowly targeted, and still under long-term safety study rather than being broadly available cures.

Fun fact

Mendel’s original pea-plant data was so mathematically clean that statistician Ronald Fisher argued in 1936 it was suspiciously close to perfect — a puzzle still debated by historians of science, some of whom suspect unconscious bias in Mendel’s assistants rather than fraud.

Sources

• Mendel, G. “Experiments on Plant Hybridization” (1866), Proceedings of the Natural History Society of Brno — full text via MendelWeb
• National Human Genome Research Institute, “1910: Fly Room” — genome.gov
• National Human Genome Research Institute, “International Consortium Completes Human Genome Project” (2003) — genome.gov
• The Nobel Prize, “The Nobel Prize in Chemistry 2020 – Popular Information” — nobelprize.org
• Britannica, “Thomas Hunt Morgan” — britannica.com