Cloning in Todays World

Keller Hinson

April 21, 2005

Biology 100

Jackson

Cloning in Todays World

Cloning is the creation of an organism that is an exact genetic copy of another. This means that every single bit of DNA is the same between the two. There are different types of cloning however, and cloning technologies can be used for other purposes besides producing the genetic twin of another organism. The following types of cloning technologies will be discussed: (1) recombinant DNA technology or DNA cloning, and (2) reproductive cloning.

Recombinant DNA Technology

The term recombinant DNA technology refers to the transfer of DNA from one organism to a self replicating genetic element such as a bacterial plasmid. The DNA of interest can then be propagated in a foreign host cell. Plasmids are self-replicating extra-chromosomal circular DNA molecules and are used to copy genes and other pieces of chromosomes to generate enough identical material for further study. To clone a gene, a DNA fragment containing the gene is isolated using restriction enzymes and then united with a plasmid that has been cut with the same restriction enzyme. Following introduction into suitable host cells, the recombinant DNA can then be reproduced along with the host cell. This technology has been around since the 1970's, and it has become a common practice in molecular biology labs today.

Reproductive Cloning

Reproductive cloning is a technology used to generate an animal that has the same nuclear DNA as another currently or previously existing animal. An example of reproductive cloning occurred in 1996 when researchers at the Roslin Institute in Scotland managed to create a lamb named Dolly. In a process called "somatic cell nuclear transfer" (SCNT), scientists transfer genetic material from the nucleus of a donor adult cell to an egg whose nucleus, and thus its genetic material, has been removed. The reconstructed egg containing the DNA from a donor cell must be treated with chemicals or electric current in order to stimulate cell division. Once the cloned embryo reaches a suitable stage, it is transferred to the uterus of a female host where it continues to develop until birth. Dolly or any other animal created using nuclear transfer technology is not truly an identical clone of the donor animal. Only the clone's chromosomal or nuclear DNA is the same as the donor. Some of the clone's genetic materials come from the mitochondria in the cytoplasm of the enucleated egg. Mitochondria, which are organelles that serve as power sources to the cell, contain their own short segments of DNA. Acquired mutations in mitochondrial DNA are believed to play an important role in the aging process. Dolly's success is truly remarkable because it proved that the genetic material from a specialized adult cell, such as an udder cell programmed to express only those genes needed by udder cells, could be reprogrammed to generate an entire new organism.

These cloning technologies are being used in a number of ways. However these technologies have met strong opposition. While some feel cloning a benefit to science and society, others are against its procedures. There are arguments that advocate the usage of cloning and arguments that advocate the opposite. Here will discuss the benefits and risks these delicate technologies pose.

Risks of Cloning

Reproductive cloning is expensive and highly inefficient. More than 90% of cloning attempts fail to produce viable offspring. More than 100 nuclear transfer procedures could be required to produce one viable clone. In addition to low success rates, cloned animals tend to have more compromised immune function and higher rates of infection, tumor growth, and other disorders. Japanese studies have shown that cloned mice live in poor health and die early. About a third of the cloned calves born alive have died young, and many of them were abnormally large. Many cloned animals have not lived long enough to generate good data about how clones age. Appearing healthy at a young age unfortunately is not a good indicator of long term survival. Clones have been known to die mysteriously. For example, Australia's first cloned sheep appeared