History dependent effects on phenotypic expression of a newly emerged gene

In this study, we investigate the history dependence of the penetrance of a newly emerged gene. Penetrance is defined as the percentage of individuals with a given genotype who exhibit the phenotype associated with that particular genotype. Here, we used the glutamine synthetase gene and its mutants with lower fitness as model genes. They were introduced into host cells of Escherichia coli deprived of the gene, and their penetrance was measured using the host having a different history: either with or without glutamine starvation. Results show that for all genes tested, the value of penetrance was higher when they were introduced into the host cell without starvation than that when introduced into the starved cell, demonstrating the history dependence of the penetrance of a newly emerged gene. In addition, genes with lower fitness showed lower penetrance, and the effect of the difference in fitness on gene penetrance also depended on the history of the host cell.