Lesson #16 of 18 in the Brain Makeover collaboration with Professor James Trefil/George Mason University, the 76ers Cheerleaders and the Science Cheerleader. See Brain Makeover Series.
#16: All life is based on the same genetic code.

All of the millions of different life forms on Earth, from amoeba to humans, use the same DNA code to produce the proteins that run the chemical reactions essential to life. This is one piece of evidence that all living things descended from a common ancestor. The fact is also the basis for genetic engineering, a technique that already plays a major role in agriculture.
In genetic engineering a gene from one organism is inserted into the DNA for another. For example, insulin for the treatment of diabetes is obtained by inserting the gene for human insulin into the DNA of bacteria, which then produce the insulin. In the United States, the great majority of commercial crops such as corn, soybeans, and cotton, have been engineered to produce chemicals to kill insect pests. Genetically engineered animals are also used to improve breeding stock  (but are too expensive to use for food).
All human somatic cells (cells that are not sperm or egg cells) contain the same DNA, but as an organism grows after conception, cells specialize by turning genes off. Typically, of the 30,000 or so genes in human DNA, less than a thousand will be operating in a given cell. For the first several cell divisions after conception, however, no genes are turned off. Such cells, which have the potential of turning into any tissue in the human body, are called embryonic stem cells. Recently, progress has been made in finding ways to turn genes back on in ordinary cells, possibly producing a different kind of stem cell.