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Hugo De Vries (1848—1935) Dutch plant physiologist and geneticist

 

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Wilhelm Ludvig Johannsen

(1857—1927)


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(1857–1927)

Danish geneticist who introduced the terms phenotype, genotype, and gene, and was one of the founders of modern genetics.

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.


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