Gregor Mendel

Gregor Mendel discovered the basic principles of heredity through experiments with pea plants, long before the discovery of DNA and genes. Mendel was an Augustinian monk at St Thomas’s Abbey near Brünn (now Brno, in the Czech Republic). He studied natural sciences and mathematics at the University of Vienna, Austria, but twice failed to obtain a teaching certificate, instead becoming a part-time assistant teacher and carrying out research in plant breeding.

His most famous experiments were done between 1857 and 1864, during which time he grew some 10,000 pea plants. Pea plants are hermaphroditic, meaning they have both male and female sex cells and usually fertilise themselves. Mendel was able to cross-breed the plants by transferring pollen with a paintbrush. He meticulously recorded a range of characteristics for each plant, including its height, pod shape, pea shape and pea colour. When plants self-fertilised, these characteristics remained consistent in the offspring.

At the time, it was widely believed that heredity worked by blending the characteristics of parents, producing offspring that were in some way diluted. Mendel showed that when two varieties of purebred plants cross-breed, the offspring resembled one or other of the parents, not a blend of the two. He found that some traits are dominant and would always be expressed in a first generation cross, while others are recessive and would not appear in this generation. However, these recessive traits re-appear in the next generation if these first-generation plants self-fertilise.

Mendel hypothesised that parents contribute some particulate substance to the offspring which determine its heritable characteristics. We now know that these particles correspond to genes made of DNA. Without any knowledge of the molecules involved, Mendel was able to infer that heritable particles are separated into gametes – eggs and sperm – and that offspring inherit one particle from each parent.

Mendel was far ahead of his time, and his work was largely ignored for the next 35 years. In 1868 he was appointed as an abbot and, overwhelmed with administrative duties, had little time left to continue his research. Late in his career, he wrote: “My scientific work brought me such satisfaction, and I am convinced the entire world will recognise the results of these studies.” He died in 1884, aged 62.

In 1900, three scientists independently confirmed his work, but it was another 30 years before his conclusions were widely accepted. Then evolutionary biologists such as Ronald Fisher realised that Mendel’s laws of inheritance could explain how natural selection could make beneficial traits become more prevalent and eliminate negative ones. His work formed part of “the modern synthesis”, a reformulation of Darwin’s ideas based on the new understanding of genetics.