During gene insertion using microinjection, transgenes are added to the:
Male pronucleus
The egg and the sperm fuse to form a zygote.The zygote stage is very brief. In the zygote we have the male and female pronucleus.The transgene is added to the male pronucleus as it is bigger. After this, the male and the femal pronuclei fuse and further divide to form the embryo which is then implanted into a surrogate mother to develop further into a full fledged organism.