Mendel, Gregor (1822–1884)

Gregor Mendel was an Augustinian monk and botanist who is considered the founder of genetics for having formulated a series of laws regulating the transmission of features through different generations of plants. In a series of experiments with peas during the 1850s and 1860s, he proved that characteristics such as size and color were combined independently in hybrid plants from different parents. He also demonstrated that there was a hierarchy in transmission of certain contrasting characteristics—for example, a crossing between a tall and a short pea plant always yielded tall—and that a given characteristic could be transmitted to further generations despite not being visibly shown in an offspring pea—two tall plants could yield a short one due to their ancestors. In the early 20th century, Mendel's laws were reinterpreted after a long period of oblivion and incorporated into the core of genetics, the discipline studying how genes convey features that are inherited in different species.

Mendel was born in a small town of the Austrian Silesia, currently part of the Czech Republic but in the mid-19th century belonging to the Austrian Empire. During his childhood, he combined animal and plant care at a family farm with formal education. His religious career started at age 21, when his family, unable to fund his studies, sent him to the Abbey of Saint Thomas in Brünn—now the city of Brno. Due to his intellectual potential, Mendel was allowed to attend the University of Vienna, where he studied physics, mathematics, and natural sciences.

The results of Mendel's degree were not fully satisfactory, due to his frail physical and psychological health. Three years after returning to Brünn (1856), he started his experiments with peas in an allotment belonging to the abbey and devoted to hybridization of agricultural variants. Mendel crossed different types of pea plants and observed the similarities and differences of their descendants. By repeating this operation various thousands of times, he obtained a large record of generations that allowed him to quantify the transmission of characteristics.

Mendel applied combinatorial mathematics to determine how often certain features—green or yellow color, round or wrinkled seeds—were transmitted over others to the offspring after the crossing of different plants. He concluded, from the frequencies of transmission, that there were dominant and recessive characteristics. The former were always preferentially transmitted, but recessive characteristics could be transmitted to further generations by the offspring despite remaining invisible during their lifetime. If, for instance, green color was a dominant characteristic and yellow was recessive, the offspring of a green and yellow plant would always be green, but could have yellow descendents.

The results of Mendel's experiments were published at the Proceedings of the Natural History Society of Brünn in 1866, after he presented them at the meetings of this society. However, the local nature of this publication, together with the state of the life sciences at that time, led Mendel's conclusions to go largely unnoticed. Only 7 years before, in 1859, Charles Darwin had published The Origin of Species and triggered an increasing debate on the mechanisms of evolution of different organisms, among them animals and plants. Despite Mendel being aware of this debate, he barely mentioned it in his paper, and this resulted in his laws not being connected with one of the main topics of late-19th-century life sciences. The growing opposition of religious institutions to Darwinism and evolution further obstructed this connection.

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