An example of a partial integral gene drive (IGD) developed by Hoermann and colleagues (2021). Separate mosquito strains were generated containing sequences for (A) the anti-Plasmodium effector peptide Scorpine (Sco, orange) fused to the somatic gene peritrophin1 (Aper1, green). Guide RNA (gRNA, red) is encoded by an artificial intron in Sco. As Cas9 (blue) is not present, the construct is inherited at Mendelian rates, allowing field testing in the absence of drive. (B) Cas9 (blue), driven by the vasa promoter (E. Marois, unpubl data). (C) Crossing the strains produces offspring carrying both the Sco payload and Cas9, allowing Sco to drive, as the homologous allele can be cleaved (black triangle) to initiate homing.