User:Eelbert2/sandbox

Fertilization
As with the case in all amphibians in the wild, fertilization is an external process. The male will clasp on the back of the female and as the eggs leave the cloaca he releases his sperm. In a laboratory setting however fertilization is done in vitro.

The egg is coated with several jelly layers including the vitelline envelope, that is later involved in the prevention of polyspermy. Sperm enters the egg by a reaction between its acrosome and the vitelline layer. This reaction is due to the response of a glycoprotein found on the eggs outer membrane that aids in the binding of the sperm to itself. Research has proven that it is a sperm surface glycoprotein (SGP) that establishes this bond through the receptors gp69/64(ZPA) and gp41(ZPC) found on the egg membranes surface. Certain proteases have also been linked to this binding in recent studies but they have not yet been repeated enough to show conclusive evidence. SGP binding is found mostly on the animal hemisphere of the egg, which confirms the theory of entry being dominantly on the animal hemisphere instead of the vegetal hemisphere.

Calcium plays a role in the fertilization of the Xenopus. High levels of extracellular calcium is the prerequisite for the blocking of polyspermy, exiting the meiotic phase and nuclear formation along with other cellular reactions. While an increase in the intracellular calcium leads to the release of the second polar body and the exocytosis of cortical granules near the eggs surface raising the vitelline layer allowing the egg to rotate freely (cortical rotation) bring the animal hemisphere into an upright position.

Model Advantages and Disadvantages
Advantages to using Xenopus are as follows. They have large embryo which aids in the process of micro-manipulation, they also lay a large number of eggs and the cost and maintenance for these embryos is relatively low. However, Xenopus is not a very useful tool when it comes to genetics. The only known genetic inventory known at the moment is X.tropicalis.