Chapter 22 - The Study of Phenotypic Variability: An Emerging Research Agenda for Understanding the Developmental—Genetic Architecture Underlying Phenotypic Variation

Abstract

This chapter deals with variability at a specific level, the organismal phenotype. The study of variability at the phenotypic level is concerned with how the architecture of development structures the translation of genetic variation and environmental effects into phenotypic variation. This is important because natural selection acts on phenotypes, but the results are interpreted and transmitted from generation to generation at the genetic level. It is interesting precisely because the relationship between variation at the genetic level and variation at the phenotypic level can be very complex. If the relationship between genetic and phenotypic variation were straightforward, the study of development would be largely irrelevant to evolutionary biology. Getting at the developmental genetic basis for variability is different from the developmental genetic basis of phenotypic variation in specific developmental contexts. The study of the evolutionary developmental biology of variation is still at a very early stage, but its conceptual framework is well developed. The study of the developmental basis for phenotypic variability addresses a higher level of abstraction in that it deals with the tendency of developmental systems to change, amplify, or reduce the expression of genetic variation at the phenotypic level. This area of study is difficult because variability arises from emergent properties of complex developmental systems. Understanding how variability arises from developmental systems requires approaches that focus on the patterns and nature of the interactions among elements in the system.