Changes

[[Image:Fertilization histology.jpg|right|thumb|250px|<small><center> Electron Scanning Micrograph of Spermatozoa in the Uterine Horn.  Copyright RVC 2008 (Courtesy of John Bredl (RVC))</center></small>]]

[[Image:Fertilization histology.jpg|right|thumb|250px|<small><center> Electron Scanning Micrograph of Spermatozoa in the Uterine Horn.  Copyright RVC 2008 (Courtesy of John Bredl (RVC))</center></small>]]

* When the spermatozoon completely penetrates the zona pellucida and reaches the perivitelline space, it settles into a bed of '''microvilli''' formed by the oocyte plasma membrane.

* When the spermatozoon completely penetrates the zona pellucida and reaches the perivitelline space, it settles into a bed of '''microvilli''' formed by the oocyte plasma membrane.

* Oocyte plasma membrane fuses with the '''equitorial segment''' and the fertilizing spermatozoon is engulfed.  

* Oocyte plasma membrane fuses with the '''equitorial segment''' and the fertilizing spermatozoon is engulfed.  

**Brought about by a fusion protein that is inactive prior to the [[Copulation_-Sperm_in_the_Female_Tract_-_Anatomy_%26_Physiology|acrosome reaction]].

**Brought about by a fusion protein that is inactive prior to the [[Sperm in the Female Tract - Anatomy & Physiology|acrosome reaction]].

* Nucleus of the spermatozoon is within the oocyte cytoplasm.

* Nucleus of the spermatozoon is within the oocyte cytoplasm.

* Sperm nuclear membrane disappears.

* Sperm nuclear membrane disappears.

''N.B: Although sperm mitochondria enters the Ooctye cytoplasm, they carry a ubiquitin signal.  They are subsequently destroyed by Ubiquiitinase and do NOT contribute to mitochondrial DNA.  Therefore mitochondial DNA is entirely from the maternal side.''

''N.B: Although sperm mitochondria enters the Ooctye cytoplasm, they carry a ubiquitin signal.  They are subsequently destroyed by Ubiquiitinase and do NOT contribute to mitochondrial DNA.  Therefore mitochondial DNA is entirely from the maternal side.''