The Full Breadth of Mendel’s Genetics

Abstract

Gregor Mendel’s “Experiments on Plant Hybrids” (1865/1866), published 150 years ago, is without doubt one of the most brilliant works in biology. Curiously, Mendel’s later studies on Hieracium (hawkweed) are usually seen as a frustrating failure, because it is assumed that they were intended to confirm the segregation ratios he found in Pisum. Had this been his intention, such a confirmation would have failed, since, unknown to Mendel, Hieracium species mostly reproduce by means of clonal seeds (apomixis). Here we show that this assumption arises from a misunderstanding that could be explained by a missing page in Mendel’s first letter to Carl Nägeli. Mendel’s writings clearly indicate his interest in “constant hybrids,” hybrids which do not segregate, and which were “essentially different” from “variable hybrids” such as in Pisum. After the Pisum studies, Mendel worked mainly on Hieracium for 7 years where he found constant hybrids and some great surprises. He also continued to explore variable hybrids; both variable and constant hybrids were of interest to Mendel with respect to inheritance and to species evolution. Mendel considered that their similarities and differences might provide deep insights and that their differing behaviors were “individual manifestations of a higher more fundamental law.”

Mendel’s pea crosses: varieties, traits and statistics

“…Mendel’s genetical studies have received a considerable amount of attention since the 150th anniversary of his 1865 lectures and 1866 paper [1, 2, 3, 4, 5, 6]. This attention broadly sought to understand Mendel’s work and intellectual position, but did not directly discuss his experimental plans nor seek to resolve the controversy, initiated by Fisher [7], concerning the statistical analysis of Mendel’s data.…”

How Political Repression Stifled the Nascent Foundations of Heredity Research before Mendel in Central European Sheep Breeding Societies

“…Soon this society became an important melting pot creating a multicultural and interdisciplinary scientific community, which shaped pre-Mendelian heredity research [41]. Sheep breeders, factory owners, businessmen, economists, and academics in Brno-united by their common interest in wool-began discussing how they might increase production and quality [42]; [43] (p. [57][58][59][60][61][62][63][64][65][66][67][68][69][70]. They were seeking a scientific basis for breeding by drawing knowledge from several fields to unify them into one interdisciplinary study.…”

“…[53]. With this statement he formulated a research question, which later motivated Gregor Mendel in his experiments with peas and hawkweed [54][55][56][57][58][59][60]. Towards the end of 1837, Nestler published a paper "Heredity in Sheep Breeding" in which he wrote: "The terms species and race in the animal kingdom correspond precisely with the term species and variety in the plant kingdom.…”

How Mendel’s Interest in Inheritance Grew out of Plant Improvement

“…Based on detailed analysis of Mendel’s letters to Nägeli, we have recently argued that the traditional interpretation that the Hieracium crossing experiments were intended to repeat the Pisum experiments, and therefore frustrated Mendel, is wrong (van Dijk and Ellis 2016). With Hieracium , Mendel moved to wild species and more clearly to fundamental research.…”

“…While Mendel had produced ca . 200 Hieracium hybrids, this had been a huge effort involving many thousands of hand emasculations and cross-fertilizations (van Dijk and Ellis 2016), so he realized that he had to make many more artificial fertilizations to obtain a sufficient number of hybrids to analyze the numerical relationships between the different types or “members of the series.” This was virtually impossible because the emasculation of the tiny flowers had to be done with lens-concentrated light, which already had almost ruined his eyesight.…”