Science history: ‘Father of modern genetics’ describes his experiments with pea plants — and proves that heredity is transmitted in discrete units — Feb. 8, 1865
Milestone: Discovery of the principles of inheritance
Date: February 8 and March 8, 1865
Or: Brno, in today’s Czech Republic
WHO: Gregor Mendel
On a cold February day, an Augustinian friar described his experiments in breeding garden plants – and gave birth to the field of modern genetics.
Gregor Mendel was an Austrian priest who spent eight years cultivating and crossing over 28,000 pea plants (Pisum sativum) in the garden of the St. Thomas Monastery in Brno (formerly Brünn), painstakingly recording details of the plants’ descent.
Mendel was actively discouraged from further research. His bishop laughed every time Mendel told him about his scientific experiments, according to a letter his abbot Cyril Napp wrote to him. in 1859.
“He asked me if I thought [sic] it seems normal for a man of your intellectual level to toil in a pea field, delving into the germinal tendencies of peas. He suggested that the propagation of peas was a subject less worthy of your curiosity than, say, the writings of the Church Fathers or the Doctrine of Grace. My dear brother Mendel, as sympathetic as I am to your research [sic]we cannot afford to make the monastery the laughing stock of the diocese. »
But Mendel was undeterred in his research – not because of a deep interest in plants, but because he wanted to reveal the principles of heredity.
He had chosen to study the plants of this unassuming legume for several reasons. First, pea plants reproduced quickly and well in both pots and in soil, according to one study. Monograph from 1866 he wrote about his research. Second, they seemed to have clear traits that they passed on to their offspring – like pink, white or red flowers – and the hybrids were perfectly fertile.
Finally, “accidental impregnation with foreign pollen, if it occurred during the experiments and was not recognized, would lead to completely erroneous conclusions,” he writes.
He identified several distinct traits to track – such as the color of the peas and their pods, the position of the flowers and the length of the stems – then cross-referenced those with different characteristics. Then he let each distinct type of plant “self-reproduce” for two years, demonstrating that the traits continued to be passed on to offspring.
Then he crossed these plants and crossed the resulting hybrids. He painstakingly mapped out all the ways traits were inherited, designating each parent’s different traits with simple labels like Aa, Bb, and Cc.
By analyzing the mathematical patterns of each subsequent generation, he deduced the basic principles of inheritance. First, he noted that certain traits were passed down in discrete units, or “particles”: if you cross a green pea plant with a yellow pea plant, you get either green or yellow offspring, not yellowish green.
He also concluded that certain traits were inherited in a “dominant” pattern. For example, if plants bred for generations to have only smooth seeds were crossed with those that had wrinkled seeds, the result would be the same. the offspring would still have smooth seeds.
When Mendel crossed hybrids, he noticed something strange: Most of the plants appeared smooth, but about a quarter appeared wrinkled. He deduced that the wrinkled trait was instead transmitted in a “recessive” manner and that the trait actually came from the grandfather plant’s generation.
Mendel was not content to study one “particle” at a time. He also crossed hybrid plants for two different traits and learned that each trait was transmitted separately, which is now known as the principle of segregation.
Mendel’s work was not recognized during his lifetime. And although Mendel is often known as the “father of genetics,” the term “genetics” was not coined until the early 1900s, when English biologist William Bateson rediscovered Mendel’s forgotten work and awareness of its primordial significance.
Soon after, some argued that Mendel’s data were “too good to be true“, and that he had to fabricate his results. 2020 study put this idea aside, showing that given the seeds available at the time, what Mendel knew, and how seeds were then classified, his results were in fact what was expected.
Decades later, research revealed that inheritance is not as simple as Mendel’s pea plants suggest: Some genes are inherited in a sex-linked manner, and other traits have incomplete “penetrance,” meaning they don’t always manifest themselves in the same way. And in early 2026, research found that some pathogenic genes that we thought were dominant do not work as we thought, which could call into question some of the fundamental principles of Mendelian inheritance.
