It has been 50 years since scientists first created DNA in a test tube, stitching ordinary chemical ingredients together to make life's most extraordinary molecule. Until recently, however, even the most sophisticated laboratories could make only small snippets of DNA -- an extra gene or two to be inserted into corn plants, for example, to help the plants ward off insects or tolerate drought.

Now researchers are poised to cross a dramatic barrier: the creation of life forms driven by completely artificial DNA.

Scientists in Maryland have already built the world's first entirely handcrafted chromosome -- a large looping strand of DNA made from scratch in a laboratory, containing all the instructions a microbe needs to live and reproduce.