A controversial issue is the possible application of new genetic engineering techniques to produce human clones. Until now, genetic engineering and cloning have been used to clone plants, single-celled organisms, amphibians and simple mammals. This led to significant advances in agriculture, industry and medicine. More recent techniques in genetic engineering have allowed scientists to clone more complex mammals and have opened up the possibility of cloning humans. Although this technology has many potential benefits, the prospect of human cloning has raised many practical, ethical and religious dilemmas that are currently being debated in society. For now, cloning of humans does not seem likely to occur in the near future. Genetic engineering involves modifying the DNA or genetic material of an organism to eliminate undesirable traits or produce desirable traits. The first form of genetic engineering dates back to scientist Gregor Mendel who carried out experiments on peas. He selected only the peas with the most desirable characteristics in order to obtain a healthier and stronger pea (McCuen 8). This method, called selective breeding, is still used today with plants and animals to increase food production. Corn plants are selectively bred to produce a larger, more flavorful kernel. Another type of genetic engineering called hybridization or crossbreeding involves breeding animals from different species to obtain the most sought-after characteristics of both. Male donkeys are crossed with female horses to produce mules, which are good working animals (Levine 1). In 1938, Hans Speman proposed cloning a mammal by transplanting the nucleus of an adult cell into a fertilized egg. This process is called nuclear transfer and was initially used to clone a frog in 1952 (Sinha 59). Through this process, nuclear DNA from a donor frog's body cell was injected into the egg cell of a recipient frog that had its nuclear genetic material removed. The fused cells divided like a normal fertilized egg and formed an embryo genetically identical to the donor frog. In 1980, mice were successfully cloned using a similar procedure. The nucleus of a body cell from an embryo taken from a pregnant mouse was placed into a fertilized egg from another mouse that had its own nucleus removed. The cell was grown in vitro until it divided and became an embryo. It was then implanted into another mouse and allowed to grow to term..