Complex sentence: In November 2015 an American research group demonstrated that an "Anopheles stephensi" with genetic modifications could be rendered incapable of transmitting malaria, and that 99.5 percent of the mutant mosquitoes' offspring were also immune.
Split into simpler sentences: In November 2015 an American research group showed that an "Anopheles stephensi" with an adjusted gen, could not pass down malaria anymore. Besides of that 99.5 percent of the offspring of the mutant mosquitoes were also immune.