There are many cases of horizontal gene transfer involving eukaryotic cells, although usually the donor would be a prokaryotic cell or a virus. The bacterial r

There are many cases of horizontal gene transfer involving eukaryotic cells, although usually the donor would be a prokaryotic cell or a virus. The bacterial residents of mealybug have lost the ability to make crucial proteins, and instead rely on the mealybug to produce them. It never had those genes in the first place, obtaining them instead through HGT. It's thus posited that eukaryotic organelles such as mitochondria and chloroplasts transferred genes to their hosts as well.[0] [0]: https://www.quantamagazine.org/cell-bacteria-mergers-offer-clues-to-how-organelles-evolved-20191003/ https://www.quantamagazine.org/cell-bacteria-mergers-offer-c...