Figure 1

A model of how overlapping functions in a gene family might obscure thermotolerance phenotypes. Single and double mutants of the HSFA1 transcription factors have no thermotolerance phenotypes [21, 23], presumably because they still cross a response threshold before the phenotype is assayed. Triple and quadruple mutant phenotypes are detected because they do not cross the threshold. A system that allows the kinetics of the response to be monitored could uncover these single and double mutant phenotypes.