Plant Phenotypes as Distributions: Johannsen's Beans Revisited.

AbstractIn the early twentieth century, Wilhelm Johannsen's breeding experiments on pure lines of beans provided empirical support for his groundbreaking distinction between phenotype and genotype, the foundation stone of classical genetics. In contrast with the controversial history of the genotype concept, the notion of phenotype has remained essentially unrevised since then. The application of the Johannsenian concept of phenotype to modularly built, nonunitary plants, however, needs reexamination. In the first part of this article it is shown that Johannsen's appealing solution for dealing with the multiplicity of nonidentical organs produced by plant individuals (representing individual plant phenotypes by arithmetic means), which has persisted to this day, reflected his intellectual commitment to nineteenth-century typological thinking. Revisitation of Johannsen's results using current statistical tools upholds his major conclusion about the nature of heredity but at the same time falsifies two important ancillary conclusions of his experiments-namely, the alleged homogeneity of pure lines (genotypes) regarding seed weight variability and the lack of transgenerational effects of within-line (within-genotype) seed weight variation. The canonical notion of individual plant phenotypes as arithmetic means should therefore be superseded by a concept of phenotype as a dual property, consisting of central tendency and variability components of organ trait distribution. Phenotype duality offers a unifying framework applicable to all nonunitary organisms.

A special role for the genotype? Some comments on Keith Baverstock: "The gene: An appraisal".

There is at present uneasiness about the conceptual basis of genetics. The gene concept has become blurred and there are problems with the distinction between genotype and phenotype. In the present paper I go back to their role in the creation of modern genetics in the early twentieth century. The terms were introduced by the Danish botanist and geneticist Wilhelm Johannsen in his big textbook of 1909. Historical accounts usually concentrate on this book and his 1911 paper "The Genotype Conception of Heredity." His bean selection experiment of 1900-1903 is generally assumed to be the source of his genotype theory. The present paper examines the scientific context and meaning of this experiment, how it was received, and how the genotype theory became securely established by the early 1910s. I argue in conclusion that the genotype/phenotype distinction, which provides the empirical basis for Johannsen's gene, was scientifically well founded when introduced and still is. Keith Baverstock's criticism does not consider the force of the bean selection experiment at the time and as a paradigm for following investigations of heredity.

The many lives of experiments: Wilhelm Johannsen, selection, hybridization, and the complex relations of genes and characters.

In addition to his experiments on selection in pure lines, Wilhelm Johannsen (1857-1927) performed less well-known hybridisation experiments with beans. This article describes these experiments and discusses Johannsen's motivations and interpretations, in the context of developments in early genetics. I will show that Johannsen first presented the hybridisation experiments as an additional control for his selection experiments. The latter were dedicated to investigating heredity with respect to debates concerning the significance of natural selection of continuous variation for evolution. In the course of the establishment of a Mendelian research program after 1900, the study of heredity gained increasing independence from questions of evolution, and focused more on the modes and mechanisms of heredity. Further to their role as control experiments, Johannsen also saw his hybridisation experiments as contributing to the Mendelian program, by extending the scope of the principles of Mendelian inheritance to quantitative characters. Towards the end of the first decade of genetics, Johannsen revisited his experiments to illustrate the many-many relationship between genes and characters, at a time when that relationship appeared increasingly complex, and the unit-character concept, accordingly, became inadequate. For the philosophy of science, the example shows that experiments can have multiple roles in a research programme, and can be interpreted in the light of questions other than those that motivated the experiments in the first place.

The plant breeding industry after pure line theory: Lessons from the National Institute of Agricultural Botany.

In the early twentieth century, Wilhelm Johannsen proposed his pure line theory and the genotype/phenotype distinction, work that is prized as one of the most important founding contributions to genetics and Mendelian plant breeding. Most historians have already concluded that pure line theory did not change breeding practices directly. Instead, breeding became more orderly as a consequence of pure line theory, which structured breeding programmes and eliminated external heritable influences. This incremental change then explains how and why the large multi-national seed companies that we know today were created; pure lines invited standardisation and economies of scale that the latter were designed to exploit. Rather than focus on breeding practice, this paper examines the plant varietal market itself. It focusses upon work conducted by the National Institute of Agricultural Botany (NIAB) during the interwar years, and in doing so demonstrates that, on the contrary, the pure line was actually only partially accepted by the industry. Moreover, claims that contradicted the logic of the pure line were not merely tolerated by the agricultural geneticists affiliated with NIAB, but were acknowledged and legitimised by them. The history of how and why the plant breeding industry was transformed remains to be written.