The Genotype-Phenotype Map: Origins, Properties, and Evolutionary Consequences

Abstract

Describing and understanding the relationship between genotypes and phenotypes, or the genotype-phenotype map, is of long-lasting interest in genetics and evolutionary biology. My dissertation focuses on understanding the origins, properties, and evolutionary consequences of genotype-phenotype maps. In Chapter 2, using yeast morphological traits, I showed that most traits are affected by a small proportion of genes, many of which have small effects while a few have large effects. To explain why many phenotypic effects are small, in the rest of Chapter 2 as well as in Chapter 3, I studied yeast morphological traits, yeast gene expression traits, and E. coli reaction flux traits and found evidence supporting the hypothesis of adaptive genetic robustness. In Chapter 4, by comparing the evolutionary rates of phenotypic traits of varying importance, I found evidence for that yeast morphological traits have evolved generally by adaptation while yeast gene expression traits have evolved largely neutrally. In Chapter 5, using yeast morphological traits, I found that increasing mutational correlation generally facilitates phenotypic evolution when the correlation is low, but constrains it when the correlation become very high. Thus, an intermediate level of mutation correlation is most conducive to phenotype evolution. In Chapter 6, using E. coli gene expression level traits and E. coli reaction flux traits, I found that genetic changes tend to reverse plastic changes when a population adapts to a new environment, suggesting that phenotypic plasticity does not generally serve as a steppingstone to genetic adaption. To sum up, this dissertation highlights the importance of incorporating genotype-phenotype maps into the study of evolution, identifies influential factors in phenotypic evolution, and thus deepens our understanding of general principles of evolution.