Wilhelm Ludvig Johannsen (February 3, 1857 - November 11, 1927) was a Danish botanist. In 1909, he coined the word gene (using the Greek for "to give birth to").

1857 births | 1927 deaths | Danish botanists | Botanists Geneticists

Born in Copenhagen, the son of an army officer, Johannsen was apprenticed to a pharmacist in 1872 and worked in Denmark and Germany, passing his pharmacist's exam in 1879. Two years later he was appointed assistant in the chemistry department at the Carlsberg laboratory under the famous chemist Johan Kjeldahl (1849-1900). Here Johannsen investigated the metabolism of dormancy and germination in seeds, tubers, and buds. In 1892 he was appointed lecturer at Copenhagen Agricultural College and eventually became professor of botany and plant physiology. Johannsen's most notable experiments concerned his so-called 'pure lines' of the self-fertile princess bean, Phaseolus vulgaris. Studying the progeny of self-fertilized plants, he selected the character of bean weight and found that both the lightest and the heaviest beans produced progeny with the same distribution of bean weights, i e they were genetically identical. He concluded that the variations in bean weight were due to environmental factors and he introduced the terms genotype (for the genetic constitution of an organism) and phenotype (for the characteristics of an organism that result from the interaction of its genotype with the environment). Johannsen favoured the view of de Vries that inheritance was determined by discrete particulate elements and abbreviated de Vries's term 'pangenes' to 'genes'. Johannsen's Arvelighedslaerens elementer (1905; 'The Elements of Heredity') was later (1909) rewritten, enlarged, and translated into German to become one of the founding texts of genetics. In 1905 Johannsen was appointed professor of plant physiology at Copenhagen University, becoming rector in 1917. Genetics was born in the first years of 1900 with the discovery that hereditary characters are carried by molecules which are physically present on chromosomes. These molecules of heredity – the genes – are responsible for the visible structures of the organisms but do not enter into those structures, which means that in every cell there are molecules which determine the characteristics of other molecules. In 1909, Wilhelm Johannsen concluded that this distinction is similar to the difference which exists between a project and its physical implementation, and represents therefore a dichotomy of the living world which is as deep as the Cartesian dichotomy between mind and body.

In order to distinguish the two types of molecules Johannsen called them genotype and phenotype, but such a dualism was almost universally rejected. At that time it was thought that proteins were responsible for both the visible structures and the hereditary characters, and all features seemed therefore reducible to a single type of molecules. The reality of the genotype-phenotype distinction was experimentally proved only in the 1940s and 50s, when molecular biology discovered that genes are chemically different from proteins, and, above all, when it became clear that genes carry linear information whereas proteins function through their three-dimensional structures.

The genotype-phenotype duality is therefore a dichotomy which divides non only two different biological functions (heredity and metabolism), but also two different physical quantities (information and energy). It is at the same time the most simple and the most general way of defining a living system, and has become the founding paradigm of modern biology, the scheme which has transformed the energy-based biology of the 19th century into the information-based biology of the 20th. Who's Who in the Twentieth Century, Oxford University Press. Systema Nature.

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