Work Step by Step
Fertilization Definition - is the process by which the male & female gametes fuse to form the Zygot. - it takes place usually in the ampullary dilated lateral part of the uterine ( fallopine ) tube a day or so of ovulation. Steps - the sperm enters the ovum which is in the stage of 2ry oocyte, by penetrating the following 3 covering of the ovum: 1- corona radiata. 2- zona pellucida. 3- cell membrane of the ovum. - penetration of the sperm is facilitated by the activity of the enzyme hyaluronidase which comes out from the head of the sperm. - it is only the head of the sperm which enters the ovum & the tail & other characteristic appearance are lost & it forms the male pronucleus. - at the same time, the 2nd meiotic division of the ovum is completed & the female pronucleus is formed. - the male pronucleus comes beside the female pronucleus & the 2 pronuclei enlarge & when they are of about equal size, they lose their membranes & fuse together to form the nucleus of the zygote. ( with the full somatic number of 46 chromosomes ). - the formed zygote is still surrounded by the zona pellucida. - the zygote then passes into prophase of the first mitotic division.