In higher mammals like humans, the only time that two organisms naturally share the exact same DNA is when they are identical twins. Identical twins are rare, only occurring if a single fertilized egg splits apart right when it begins to grow. Cloning is a technique in which scientists artificially replicate this, producing offspring identical to the parent or another organism. It's a difficult process, but cloning is one of several ways that scientists are now using our knowledge of DNA to engineer new characteristics into organisms, by adding to or changing DNA strands. Through this genetic engineering, scientists have produced plants that create their own insecticides and body cells that glow in the dark to help locate diseased tissue. By altering the sequence and types of DNA molecules in a fertilized cell, it may someday be possible to grow new body parts to replace those that have been damaged in an accident or by cancer.

According to the passage, which of the following best describes genetic engineering?