Plant Phenotypes as Distributions: Johannsen's Beans Revisited

Area of Science:

• Genetics
• Plant Biology
• Evolutionary Biology

Background:

• Wilhelm Johannsen's early 20th-century experiments established the phenotype-genotype distinction, a cornerstone of classical genetics.
• The concept of phenotype has remained largely unchanged since Johannsen's work.
• Applying Johannsen's phenotype concept to modular, nonunitary plants requires reevaluation.

Purpose of the Study:

• To reexamine the application of Johannsen's phenotype concept to modular plants.
• To investigate Johannsen's use of arithmetic means to represent plant phenotypes.
• To propose an updated concept of phenotype for nonunitary organisms.

Main Methods:

• Revisiting Wilhelm Johannsen's bean breeding experiments.
• Applying modern statistical tools to analyze historical data.
• Analyzing seed weight variability and transgenerational effects within pure lines.

Main Results:

• Johannsen's core conclusion on heredity is supported.
• Two ancillary conclusions are falsified: pure lines are not homogeneous regarding seed weight variability, and transgenerational effects exist.
• Johannsen's representation of phenotypes as arithmetic means is challenged.

Conclusions:

• The canonical notion of individual plant phenotypes as arithmetic means should be replaced.
• Phenotype should be understood as a dual property encompassing central tendency and variability.
• This dual phenotype concept offers a unifying framework for nonunitary organisms.