Re: What causes a cell to divide into so many parts?

Thank you for writing, Jennifer.  Your question requires just a little 
interpretation, and I'm going to answer based on what I think you mean, but 
if I've missed your point PLEASE let me hear from you again, okay?  Anyway, 
here goes:

The question I think you are asking is:  how can one cell, namely a 
fertilized egg, divide to produce the many different specialized tissues 
that make up most multicellular organisms?  

The simple answer is:  genes!  Within that one original cell, the fertilized 
egg containing paternal and maternal DNA, is the whole "blueprint" for how 
to make an organism.  Genetic cues prompt that one cell to divide,  making 
two cells, those two cells divide to make four, and pretty soon you have a 
ball of a few hundred cells which all look pretty much the same.  That's 
when the genes really kick in and cause some of those cells to start 
behaving differently from their neighbors.  Through this genetic regulation, 
subgroups of cells are able to differentiate into different tissue types, 
and give rise to all the different kinds of specialized cells that a body 
needs to function.  

As you might have guessed, I have sort of oversimplified the process for the 
purposes of answering your question--many people have spend their entire 
careers studying just one tiny part of this whole marvelous process.  If you 
have more specific questions now that you have the general overview, I would 
be happy to hear from you again, especially if I've misinterpreted your 
question.  I've also included a website below that has nicely organized 
general information about developmental biology, cell division, etc. that 
you might enjoy browsing through.

Warm Regards,

Jen
 http://
biology.miningco.com/science/biology