How can genes be used to trains a species origins?

<h3>How can genes be used to trains a species origins?</h3>

For example: Apples grow all over the world but they through their genes scientists know they originated from Kazakhstan.

How do scientist examine the DNA in this manner to find where the species originated?

Also is there a science that studies this? If so what is it called?
Trace* not "trains". Sorry a yahoo spell check error...


<strong>Kazakhstan best answer:</strong>
<p><i>Answer by Anh Thu Nguyen</i><br/>http://books.google.com/books?id=LnPeZdz5X4sC&pg=PA230&lpg=PA230&dq=How+can+genes+be+used+to+trains+a+species+origins%3F&source=bl&ots=c8fTH59KxN&sig=0CTIZFBfk75TIdup8-iVmBROpS0&hl=en&ei=kiIyTfe9NsGclgeF8aDQCg&sa=X&oi=book_result&ct=result&resnum=7&ved=0CEMQ6AEwBg#v=onepage&q&f=false

P.S. : Long book , dude !!! :D</p>
<p><strong>dina market atyrau kazakhstan 23-01-2012 DSCN3285</strong>
<img alt="Kazakhstan" src="http://farm8.staticflickr.com/7173/6745392807_a87eaa31c0.jpg" width="400"/><br/>
<i>Image by <a href="http://www.flickr.com/photos/42619839@N00/6745392807">DrJohnBullas</a></i>
dina market atyrau kazakhstan 23-01-2012</p>

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