Researchers implanted two sperm in an egg with its nucleus removed and modified the sperm with epigenome editing, turning certain genes on and off. Mammalian reproduction usually needs one sperm and one oocyte (egg) to create a zygote that develops in the womb until it becomes a new organism. Earlier this year, researcher Yanchang Wei at Shanghai Jiao Tong University in China succeeded at creating mouse embryos from two sperm cells that were implanted into an egg after its nucleus had been removed. Related Story Scientists Grow Mouse Embryos in Space“Mammals are diploid creatures,” Wei said in a study recently published in PNAS. In another type of androgenesis, both a sperm and egg form a zygote, but the genome of the female is eliminated.