text: do brothers who are not twins have the same dna?   only identical twins share the same dna...fraternal twins have their own unique dna.  here is the proof:  "dna is a cellular acid that carries an individual's unique genetic code. identical twins are formed from the same fertilized egg and are thought to be the only people with virtually identical genetic profiles."   http://www.usatoday.com/news/nation/2004-06-03-twins-dna_x.htm  "the dna profiles for identical twins will be identical."  http://www.genetree.com/product/twin-dna-testing.asp  "identical twins, formed when one fertilized egg splits, are the only people in the world with identical dna. fraternal twins, on the other hand, are formed when two different eggs are fertilized. genetically speaking, fraternal twins are no closer than normal siblings, sharing only about 50% of their genes."   http://ask.yahoo.com/ask/20010213.html  "as everyone knows, there are two kinds of twin, fraternal and identical. fraternal twins develop from two independently fertilized eggs, so their dna is different. identical twins are a different story. if you and your sibling are identical twins, then you two were pretty close--so close that at one point you were a single cell together, a fertilized egg known as a "zygote." usually a zygote, with its complete set of dna, divides into two cells, then the two cells divide into four, the four into eight, and so on until a human being is formed (ok, that was simplified, but we'll be here for a semester otherwise). the dna in each cell is identical."  http://www.straightdope.com/mailbag/mtwinsdna.html  i guess that is enough evidence!  lol