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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.
