"Double mutants" refers to organisms or individuals that have two different or additional genetic mutations compared to the normal or wild-type organism. Full definition
Further, B6 Fabp4 and ApoE double mutant mice show improved lipid metabolism and decreased susceptibility to atherosclerosis compared to B6 - ApoE single mutant mice. (jax.org)
First, increased endoderm specification in toddler; lefty2 double mutants does not alleviate toddler mutant defects (Figures 1 and 2). (elifesciences.org)
(B) In contrast, embryos from torY9 psqrum double mutant females show terminal defects resembling the psqrum single mutant phenotype. (genetics.org)