Wilhelm Johannsen

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Danish botanist and geneticist (1857–1927)

Johannsen was born in the Danish capital Copenhagen. On leaving school in 1872 he became apprenticed to a pharmacist as his father could not afford university fees. From his work in Danish and German pharmacies, Johannsen taught himself chemistry and developed an interest in botany. In 1881 he began work under Johan Kjeldahl in the chemistry department of the Carlsberg laboratories, investigating dormancy in seeds, tubers, and buds.

In 1892 Johannsen became lecturer at the Copenhagen Agricultural College. On reading Francis Galton's Theory of Heredity he was impressed by experiments demonstrating that selection is ineffective if applied to the progeny of self-fertilizing plants. Johannsen repeated this work using the Princess bean, but found that selection did work on the offspring of a mixed population of self-fertilizing beans. It was only when plants were derived from a single parent that selection had no effect. He called the descendants of a single parent a ‘pure line’ and argued that individuals in a pure line are genetically identical: any variation among them is due to environmental effects, which are not heritable. In 1905 he coined the terms genotype to describe the genetic constitution of an individual, and phenotype, to describe the visible result of the interaction between genotype and environment.

Johannsen explained his ideas in On Heredity and Variation (1896), which he revised and lengthened with the rediscovery of Gregor Mendel's laws and reissued as Elements of Heredity in 1905. The enlarged German edition of this work became available in 1909 and proved the most influential book on genetics in Europe. In the same year Johannsen proposed the term genes to describe Mendel's factors of inheritance. Johannsen's research, with its emphasis on the quantitative variation of characters in populations and the application of statistical methods, played a major role in the development of modern genetics from 19th-century ideas.

In 1905 Johannsen became professor of plant physiology at Copenhagen University and was made rector of the University in 1917. He spent his later years writing on the history of science.

Danish botanist and geneticist who was a pioneer in the field of experimental genetics.

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Wilhelm Ludvig Johannsen
Born	3 February 1857(1857-02-03) Elsinore, Denmark
Died	11 November 1927 (aged 70) Copenhagen, Denmark
Nationality	Denmark
Fields	Genetics Plant physiology
Institutions	University of Copenhagen
Alma mater	University of Copenhagen
Known for	proving the constancy of the genome defining gene, genotype and phenotype

Wilhelm Johannsen (3 February 1857 - 11 November 1927) was a Danish botanist, plant physiologist and geneticist. He was born in Copenhagen. While very young, he was apprenticed to a pharmacist and worked in Denmark and Germany beginning in 1872 until passing his pharmacist's exam in 1879. In 1881, he became assistant in the chemistry department at the Carlsberg Laboratory under the chemist Johan Kjeldahl. Johannsen studied the metabolism of dormancy and germination in seeds, tubers and buds. He showed that dormancy could be broken by various anesthetic compounds, such as diethyl ether and chloroform. In 1892, he was appointed lecturer at Royal Veterinary and Agricultural University and later became professor of botany and plant physiology. He taught plant physiology^[1]. His most well-known research concerned so-called pure lines of the self-fertile common bean. He was able to show that even in populations homozygous for all traits, i.e. without genetic variation, seed size followed a normal distribution. This was attributable to resource provision to the mother plant and to the position of seeds in pods and of pods on the plant. This led him to coin the terms phenotype and genotype. His findings led him to oppose contemporary Darwinists, most notably Francis Galton and Karl Pearson, who held the occurrence of normal distributed trait variation in populations as proof of gradual genetic variation on which selection could act^[2]. Only with the modern evolutionary synthesis, was it established that variation needed to be heritable to act as the raw material for selection. The terms phenotype and genotype were created by Wilhelm Johannsen and first used in his paper Om arvelighed i samfund og i rene linier^[3] and in his book Arvelighedslærens Elementer^[4]. This book was rewritten, enlarged and translated to German as Elemente der exakten Erblichkeitslehre^[5]. It was in this book Johannsen introduced the term gene. This term was coined in opposition to the then common pangene that stemmed from Darwin's theory of pangenesis. The book became one of the founding texts of genetics. Also in 1905, Johannsen was appointed professor of plant physiology at the University of Copenhagen , becoming vicechancelor in 1917. In December 1910, Johannsen was invited to give an address before the American Society of Naturalists. This talk was printed in the American Naturalist^[6]. In 1911, he was invited to give a series of four lectures at Columbia University^[7]

Miscellaneous

Corresponding member of the Academy of Natural Sciences of Philadelphia (elected 1915).

References

1. ^ Warming, Eug. & W. Johannsen (1895) Den almindelige Botanik (General Botany): En Lærebog, nærmest til Brug for Studerende og Lærere. 3rd edn, Kjøbenhavn. 4th edn by Warming and Johannsen 1900-01). German edn 1907-09: Lehrbuch der allgemeinen Botanik (from the 4th edn, by E. P. Meinecke). Berlin, Borntraeger. 667 pp.
2. ^ Roll-Hansen, Nils (1979) The Genotype Theory of Wilhelm Johannsen and its Relation to Plant Breeding and the Study of Evolution. Centaurus 22 (3): 201–235
3. ^ Johannsen, W. (1903) Om arvelighed i samfund og i rene linier. Oversigt over det Kongelige Danske Videnskabernes Selskabs Forhandlinger, vol. 3: 247-270. German ed. Erblichkeit in Populationen und in reinen Linien (1903) Gustav Fischer, Jena scanned fulltext
4. ^ Johannsen, W.L. (1905) Arvelighedslærens elementer (The Elements of Heredity). Copenhagen.
5. ^ Johannsen, W. (1909) Elemente der exakten Erblichkeitslehre. Gustav Fischer, Jena. scanned fulltext
6. ^ Johannsen, W. (1911) The Genotype Conception of Heredity. American Naturalist 45 (531): 129-159.
7. ^ Anon. (1911) Professor Johannsen's Columbia Lectures. Science N.S. 34 (876): 484.

• Anker, Jean (1932) Wilhelm Johannsen, pp. 177-180 in: Meisen, V. Prominent Danish Scientists through the Ages. University Library of Copenhagen 450th Anniversary. Levin & Munksgaard, Copenhagen.
• Roll-Hansen, Nils (1983) The Death of Spontaneous Generation and the Birth of the Gene: Two Case Studies of Relativism. Social Studies of Science 13 (4): 481-519.
• Kim, Kyung-Man (1991) On the Reception of Johannsen's Pure Line Theory: Toward a Sociology of Scientific Validity. Social Studies of Science 21 (4): 649-679.

External links

• Wilhelm Johannsen Centre for Functional Genome Research
• Image gallery
• 6 min silent mowie showing Johannsen in action as teacher and scientist

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