Hormones, Fertilization, & Punnet Square

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The steps in the process of the fertilization of an ovum are:

1. Capacitation of the sperm
In order to penetrate the ovum, the sperm needs to release seminal plasma proteins, reorganize the proteins and lipids in its plasma membrane and decrease its intracellular pH (Bowen, 2000). These changes, or capacitation of the sperm, occur in the female reproductive track once the sperm is ejaculated. This capacitation allows the sperm to be more motile and its cell membrane weakens allowing for the release of acrosomal hydrolytic enzymes latter on in the process (Snyder, 2011).

2. Binding of the sperm to the zona pellucida
Once capacitated, the sperm can attach to the outer membrane of the oocyte called zona pellucida through a glycoprotein that functions as receptor for the sperm (Bowen, 2000). This binding can only occur in the first 24 hours after ovulation (Chute, 2009).

3. Acrosomal Reaction
The sperm starts to penetrate the zona pellucida by releasing acrosomal hydrolytic enzymes that destroy the area of the zona pellucida that surrounds the sperm head (Bowen, 2000; Snyder, 2011). During this process, the sperm will lose its acrosomal content (Snyder, 2011).

4. Penetration
The constant release of enzymes by the acrosome leaves the head of the sperm without any protection in its inner acrosomal membrane (Bowen, 2000). This facilitates rapid absorption of the head into the cytoplasm of the oocyte at which point the sperm loses its midpiece and tail (Bowen, 2000; Snyder, 2011). The oocyte completes meiosis II when the sperm is integrated in the oocyte cytoplasm (Snyder, 2011). When this phase is completed, the male and female pronuclei fuse producing a zygote (Snyder, 2011).

5. Block to Polyspermy or Zona Reaction
The oocyte can only accept one sperm in order to continue its developing process toward an embryo. Once a sperm is absorbed, a series of metabolic reaction depolarize the membrane destroying the sperm receptors and any sperms that may be attached to them (Bowen, 2000; Chute, 2009). The oocyte that is ...