Model organism containing a mutation in a pathway (e.g., metabolic or signal transducing) that does not itself cause a change in phenotype, but makes the organism more sensitive to another change elsewhere in the pathway.
Source:
PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 803 (https://doi.org/10.1515/pac-2015-1202)