What is the method of producing a genetically identical copy of an organism called?

The method of producing a genetically identical copy of an organism is called reproductive cloning. This technique involves creating a new organism that has the same genetic material as the original, thereby producing a clone. This process typically entails taking a somatic (non-reproductive) cell from the organism to be cloned and transferring its nucleus into an unfertilized egg cell from which the nucleus has been removed. The egg cell is then stimulated to divide and develop into an embryo, which can be implanted into a surrogate mother to develop into a fully formed organism that is genetically identical to the donor.

Other methods mentioned in the choices, such as gene therapy, somatic cell nuclear transfer, and genetic engineering, serve different purposes. Gene therapy involves altering the genes within an individual's cells to treat or prevent disease, while somatic cell nuclear transfer is a specific technique used in reproductive cloning. Genetic engineering generally refers to the manipulation of an organism's genes using biotechnology but does not necessarily lead to the creation of an identical organism. Thus, reproductive cloning clearly identifies the process of creating a genetically identical copy, making it the most accurate answer.