In what process do male and female reproductive cells join during sexual reproduction?

Answer 1

Male sperms are left in the vagina of the female from where they travel to the fallopian tubes. If the ovum (=egg) is present in the fallopian tube then the fertilization occurs.

Following events occur during Fertilization:

A layer of glycoproteins and plasma proteins is removed enzymatically when the sperms reach the uterus. Cholesterol molecules are lost from the plasma membrane of the head region of sperms. This loosens the membrane in that region. Further, the calcium ion intake of sperms increases. All these events are collectively termed as capacitation.

When the sperm reaches the secondary oocyte(the state of the egg) , the acrosomal reactions starts. The cell membrane surrounding the acrosome ruptures, releasing the hyaluronidase and Proteases. These enzymes create a path for the sperms, through the granulose membrane, that surrounds the egg. Further an acrosomal enzyme digests the zona pellucida layer that also surrounds the egg. Membrane of a sperm fuses with the membrane of the egg. The zona pellucida layer is now thickened by the action of cortical granules present in the egg. Thickening prevents any other sperm from fusing with egg. This is called as cortical reaction. The egg completes its cell cycle (as it is arrested in Meiosis II) and the second polar body is formed that immediately degenerates.

The nuclei of the sperm swells and chromatins are now less tightly coiled. The nuclei of the sperm and egg are called pronuclei. Both the pronuclei fuse and the fertilization is complete as a zygote is formed.

Answer 2

Fertilization