by PoolBoy

Created on: July 28, 2010

The development of a new organisms in sexual reproduction begins with two cells, one being a sperm cell and the other an egg cell.  The egg cell provides the nutrients in the form of embryonic fluid for the organism, while the sperm cell is specifically designed as a transporter of DNA to ensure genetic diversity. 

Initial Contact and the Fast Block

When the sperm contacts the egg, the sperm is drawn to the egg via a chemical excretion by the egg itself.  If the sperm and the egg are the same species, a tube is created by the head of the sperm through the membrane of the egg allowing it to enter.  At the point of contact sodium channels are opened allowing an influx of positively charged sodium channels, the rapid change in voltage on the inside and concurrent negative charge on the outside membrane of the egg blocks other incoming sperm from binding.  This stage is termed “The fast block to Polyspermy.” 

The Next Stage and Slow Block

The next stage which takes longer and is correctly labeled “The Slow Block to Polyspermy”.  As the sperm and egg cell fuse, the egg cell’s endoplasmic reticulum releases stored calcium which when bound to the plasma membrane permanently ensure no other sperm enter the cell. 

Formation, Division, and the Four Stages

The sperm and the egg cell separately only have half the set of necessary chromosomes and are termed haploid.  When the sperm and egg cell nuclei combine, each half set becomes on full set which is genetically different from either parent.    The cell is now a zygote.  The single zygote cell then duplicates multiple times replicating exact copies of its DNA in a process called mitosis.  It is important to note that the cytoplasm volume is shared by all cells established from the original cell to ensure the correct size of the forming embryo and its necessary nutrients for success. While the cytoplasm is shared, the chromosomes themselves duplicate before cell division generating to identical copies of DNA before division.  The division of these cells is a four stage process.  The first is Prophase in which the chromosomes of the cell condense into tight bundles.  Next is Metaphase in which the bundles line up in the center of the cell.  In Anaphase each chromosome pair is pulled to opposite sides by spindle fibers aligned on their designated side.  Finally, Telophase is when the membrane of the

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