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 best-known research concerned so-called pure lines of the self-fertile common bean. He was able to show that even in populationshomozygous 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.
He created the terms phenotype and genotype, first using them in his book in German as Elemente der exakten Erblichkeitslehre (Elements of the exact theory of heredity).[3][4] This book was based in large part on Om arvelighed i samfund og i rene linier ("On heredity in society and in pure lines")[5] and in his book Arvelighedslærens Elementer.[6] It was in this book Johannsen also introduced the term gene.[7] 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.
^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.
^Johannsen, W. (1909). Elemente der exakten Erblichkeitslehre [Elements of the exact theory of heredity] (in German). Jena, Germany: Gustav Fischer. p. 123. Johannsen distinguished between an organism's outward appearance (which he designated as its "phenotype") and its inherent genetic heritage (which he designated as its "genotype"). He stressed that an organism's appearance need not correspond exactly to its genetic heritage. So on p. 123 he defines "phenotype": "Darum könnte man den statistisch hervortretenden Typus passend als Erscheinungstypus bezeichnen oder, kurz und klar, als "Phaenotypus". 1) … Ein gebener Phaenotypus mag Ausdruck einer biologischen Einheit sein; er braucht es aber durchaus nicht zu sein. 1) Von φαίν-ομαι, scheinen." (Therefore one could designate the statistically prominent type appropriately as a type of appearance or, clearly and concisely, as a "phenotype". 1) … A given phenotype may be an expression of a biological unit; but it definitely need not be so. 1) From φαίν-ομαι, to appear.)
^Johannsen, W. (1909). Elemente der exakten Erblichkeitslehre [Elements of the exact theory of heredity] (in German). Jena, Germany: Gustav Fischer. p. 130. Johannsen coins the term "genotype" on p. 130, where he stresses the distinction between phenotype and genotype: "Die Art, wie die Phaenotypen sich manifestieren, … der abgeleitete Begriff genotypischer Unteschied wird uns aber vielfach von Nutzen sein." (The way that the phenotype manifests itself, whether it shows itself by traits that [can be] examined qualitatively or quantitatively, says absolutely nothing beforehand about the genes. Very conspicuous phenotypic differences could show themselves where no genotypic difference is present, and there are also cases where in the case of genotypic variety, the phenotypes are alike. Thus it is precisely of the greatest importance to separate clearly the concept of phenotype (a type of appearance) from the concept of genotype (one might say a type of plan). We will admittedly not be able to operate with this latter concept – a genotype just does not appear in pure form ; the derived concept of a genotypic difference will, however, often be of use to us.)
^Johannsen, W.L. (1905) Arvelighedslærens elementer (The Elements of Heredity). Copenhagen.
^Johannsen, W. (1909). Elemente der exakten Erblichkeitslehre [Elements of the exact theory of heredity] (in German). Jena, Germany: Gustav Fischer. p. 124. From p. 124: "Dieses "etwas" in den Gameten bezw. in der Zygote, … – kurz, was wir eben Gene nennen wollen – bedingt sind." (This "something" in the gametes or in the zygote, which has crucial importance for the character of the organism, is usually called by the quite ambiguous term Anlagen [primordium, from the German word Anlage for "plan, arrangement ; rough sketch"]. Many other terms have been suggested, mostly unfortunately in closer connection with certain hypothetical opinions. The word "pangene", which was introduced by Darwin, is perhaps used most frequently in place of Anlagen. However, the word "pangene" was not well chosen, as it is a compound word containing the roots pan (the neuter form of Πας all, every) and gen (from γί-γ (ε)ν-ομαι, to become). Only the meaning of this latter [i.e., gen] comes into consideration here ; just the basic idea – [namely,] that a trait in the developing organism can be determined or is influenced by "something" in the gametes – should find expression. No hypothesis about the nature of this "something" should be postulated or supported by it. For that reason it seems simplest to use in isolation the last syllable gen from Darwin's well-known word, which alone is of interest to us, in order to replace, with it, the poor, ambiguous word Anlage. Thus we will say simply "gene" and "genes" for "pangene" and "pangenes". The word gene is completely free of any hypothesis ; it expresses only the established fact that in any case many traits of the organism are determined by specific, separable, and thus independent "conditions", "foundations", "plans" – in short, precisely what we want to call genes.)
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. JSTOR284846
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. JSTOR285343
