Spermatozoa surface membrane and that of the oocyte

Spermatozoa swim strongly in the direction of the oocyte and through the outer layers (Heffner and Schust, 2010). The underlying attraction of the spermatozoa towards the egg should be chmotactic (Heffner and Schust, 2010).

b) Name of stage: Capacitation
Brief explanation:
The spermatozoon swim towards the egg and collide with it. Normally several spermatozoa attach themselves to the egg (Heffner and Schust, 2010). Contact of the spermatozoa with the zona pellucida triggers the acrosome reaction (Heffner and Schust, 2010).

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c) Name of stage: Penetration
Brief explanation:
Aided by the acrosome enzymes they dissolve the egg membrane allowing the spermatozoon entry to penetrate the zona pellucida (Heffner and Schust, 2010). It’s just the head containing the nucleus and middle of the spermatozoa that go inside the flagellum is left outside (Heffner and Schust, 2010).

d) Name of stage: Cortical reaction
Brief explanation:
Fusion of the spermatozoon surface membrane and that of the oocyte triggers the cortical reaction (Heffner and Schust, 2010). Cortical granules harden the zona pellucida, stopping any other spermatozoa from entering (Heffner and Schust, 2010).

e) Name of stage: Fusion
Brief explanation:
The spermatozoon nucleus is currently inside the ovum (Heffner and Schust, 2010). Formation of a diploid zygote is now underway as the nuclei of the ovum and spermatozoon fuse (Heffner and Schust, 2010).

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