A key question in biology is how genetically identical cells achieve varied appearances and behaviors. These distinct cell states are realized by variations in gene expression within certain cells in the population; different genes are turned “on” or “off” in these cells. These variations in gene expression can lead to different phenotypes within a population of genetically identical cells. For example, variations in gene expression can lead some cells in a population of genetically identical bacteria to become antibiotic tolerant while other cells in the population remain suspectable to antibiotics. This project will address how variations in gene expression lead to important phenotypic changes in bacteria. To complement the research, an interactive series of lessons on mathematics in biology will be developed for high school students. These lessons will be distributed through a series of teacher workshops. Irreversibility, hysteresis, and multistability in cell state have been quantitatively studied in a handful of specific bacterial systems — B. subtilis sporulation, the lac repressor, and the lysis-lysogeny switch are now classic examples. Here, the investigators seek to expand the understanding of these concepts to the genomic scale: the investigators will examine the time scales of reversibility, and the prevalence of irreversibility, following transient repression of all genes with known function in E. coli. To accomplish this, the investigators will develop a new r