Punnett squares and hybrid crosses: how Mendelians learned their trade by the book

Abstract

The rapid reception of Gregor Mendel's paper ‘Experiments on plant hybrids’ (1866) in the early decades of the twentieth century remains poorly understood. We will suggest that this reception should not exclusively be investigated as the spread of a theory, but also as the spread of an experimental and computational protocol. Early geneticists used Mendel's paper, as well as reviews of Mendelian experiments in a variety of other publications, to acquire a unique combination of experimental and mathematical skills. We will analyse annotations in copies of Mendel's paper itself, in early editions and translations of this paper, and in early textbooks, such as Reginald Punnett's Mendelism (1905) or Wilhelm Johannsen's Elemente der exakten Erblichkeitslehre (1909). We will examine how readers used copies of such works to reproduce the logic behind Mendelian experiments, either by recalculating results, or by retracing the underlying combinatorial reasoning. We will place particular emphasis on the emergent role of diagrams in teaching and learning the practice of Mendelian genetics.

Detection of maternal carriers of common α-thalassemia deletions from cell-free DNA

“…frequencies or medians). Punnett Square was used to estimate population genotype and phenotype frequency 23 .…”

Practicing virology: making and knowing a mid-twentieth century experiment with Tobacco mosaic virus

“…This sort of closer reading and (re-) interpretation is integral to science practice. For example, Staffan Müller-Wille and Giuditta Parolini inspected copies of Mendel’s pea breeding manuscript, finding that readers “actively engaged with the text” by “rehearsing calculations and by employing Mendel’s notation system” (Müller-Wille & Parolini, 2020 , p. 157). The annotations and underlining revealed what the reader “deemed most important” (Müller-Wille & Parolini, 2020 , p. 153).…”

“…For example, Staffan Müller-Wille and Giuditta Parolini inspected copies of Mendel’s pea breeding manuscript, finding that readers “actively engaged with the text” by “rehearsing calculations and by employing Mendel’s notation system” (Müller-Wille & Parolini, 2020 , p. 157). The annotations and underlining revealed what the reader “deemed most important” (Müller-Wille & Parolini, 2020 , p. 153). Today, genetics students learn to use Punnett’s square for visualizing the outcome of genetic crosses of dominant and recessive genes.…”

“…Today, genetics students learn to use Punnett’s square for visualizing the outcome of genetic crosses of dominant and recessive genes. This “interplay between text and image” (Müller-Wille & Parolini, 2020 , p. 163) and annotation, for us, was an important part of a process that revealed Holmes’ ideas, to identify experimental materials and methods, and to design complementary experiments. Later, we repeated this process as a tool to troubleshoot possible errors in reworking the pepper experiment.…”

“…Later, we repeated this process as a tool to troubleshoot possible errors in reworking the pepper experiment. As Müller-Wille and Parolini write, this “active engagement” is a fundamental aspect of research “alongside the observations conducted at the lab bench and the experimental garden” to interpret and gain “practical knowledge” (Müller-Wille & Parolini, 2020 , pp. 164, 165).…”