Before the fusion of the spermcell and the oocyte in the tuba uterina the spermcell has to undergo two processes, capacitation and the acrosomal reaction. Capacitation of the spermcell takes place during its stay in the female tract. It consists of removing the semen fluids around the spermcell The acrosomal reaction only occurs very near the oocyte
After penetrating the corona radiata and the zona pellucida the membranes of the oocyte and the spermcell fuse.
The oocyte ends its second meiotic division. There are now two pronuclei in the cell, a male and a female one, who are both haploid. Their DNA joins into a diploid zygote after which the first cleavage can commence.
