The phrase "to fertilize the egg" means to join or combine a sperm cell and an egg cell in order to start the development of a baby or embryo. Full definition
Twenty healthy mouse pups were born after fertilised eggs from the treated ovaries were implanted into surrogate mothers (Proceedings of the National Academy of Sciences, DOI: 10.1073 / pnas.1001198107). (newscientist.com)
The other genes it contains are important for production of fully mature, motile sperm capable of fertilising an egg in the normal way. (newscientist.com)
Scientists are also able to track individual proteins as fertilised egg cells divide. (oru.se)