The genetic code in bacteria and humans is different, therefore, bacteria cannot be used to make human proteins. Genetic engineers have not yet been able to successfully introduce a human gene in a non-human animal. The idea of genetically engineered, transgenic organisms has gone from the realm of science fiction to science fact. Scientists have the technical capability to clone humans, but federal research ethics panels prohibit human cloning research in the U.S. 33. Transgenic therapy, introducing a functioning gene into a stem cell line to replace a non-functioning gene, has been used to correct an immune deficiency in patients lacking a specific enzyme involved in the immune response.
Genetic recombination is a key feature in the evolution of life.
In studies of identical twins separated at birth, scientists have shown that a complex trait such as intelligence is genetically determined and that environmental factors cannot influence this trait. Darwin's ideas on evolution were based on the differences between the DNA of man and apes. In humans, there are no obvious signs that a female is ovulating. This probably evolved to sustain male interest up throughout the menstrual cycle. Inheritance of a trait is usually controlled by several genes.