UNIT 4:What is Cloning?

Clones are organisms that are exact genetic copies. Every single bit of their DNA is identical.

Clones can happen naturally—identical twins are just one of many examples. Or they can be made in the lab. Below, find out how natural identical twins are similar to and different from clones made through modern cloning technologies.

How Is Cloning Done?

Many people first heard of cloning when Dolly the Sheep showed up on the scene in 1997. Artificial cloning technologies have been around for much longer than Dolly, though.

There are two ways to make an exact genetic copy of an organism in a lab: artificial embryo twinning and somatic cell nuclear transfer.

1. Artificial Embryo Twinning

Artificial embryo twinning is a relatively low-tech way to make clones. As the name suggests, this technique mimics the natural process that creates identical twins.

In nature, twins form very early in development when the embryo splits in two. Twinning happens in the first days after egg and sperm join, while the embryo is made of just a small number of unspecialized cells. Each half of the embryo continues dividing on its own, ultimately developing into separate, complete individuals. Since they developed from the same fertilized egg, the resulting individuals are genetically identical.

Artificial embryo twinning uses the same approach, but it is carried out in a Petri dish instead of inside the mother. A very early embryo is separated into individual cells, which are allowed to divide and develop for a short time in the Petri dish. The embryos are then placed into a surrogate mother, where they finish developing. Again, since all the embryos came from the same fertilized egg, they are genetically identical.

2. Somatic Cell Nuclear Transfer

Somatic cell nuclear transfer (SCNT), also called nuclear transfer, uses a different approach than artificial embryo twinning, but it produces the same result: an exact genetic copy, or clone, of an individual. This was the method used to create Dolly the Sheep.

What does SCNT mean?

Somatic cell: A somatic cell is any cell in the body other than sperm and egg, the two types of reproductive cells. Reproductive cells are also called germ cells. In mammals, every somatic cell has two complete sets of chromosomes, whereas the germ cells have only one complete set.

Nuclear: The nucleus is a compartment that holds the cell's DNA. The DNA is divided into packages called chromosomes, and it contains all the information needed to form an organism. It's small differences in our DNA that make each of us unique.

Transfer: Moving an object from one place to another. To make Dolly, researchers isolated a somatic cell from an adult female sheep. Next they removed the nucleus and its entire DNA from an egg cell. Then they transferred the nucleus from the somatic cell to the egg cell. After a couple of chemical tweaks, the egg cell, with its new nucleus, was behaving just like a freshly fertilized egg. It developed into an embryo, which was implanted into a surrogate mother and carried to term. (The transfer step is most often done using an electrical current to fuse the membranes of the egg and the somatic cell.)

The lamb, Dolly, was an exact genetic replica of the adult female sheep that donated the somatic cell. She was the first-ever mammal to be cloned from an adult somatic cell.

How does SCNT differ from the natural way of making an embryo?

Natural fertilization, where egg and sperm join, and SCNT both make the same thing: a dividing ball of cells, called an embryo. So what exactly is the difference between the two?

An embryo's cells all have two complete sets of chromosomes. The difference between fertilization and SCNT lies in where those two sets come from.

In fertilization, the sperm and egg have one set of chromosomes each. When the sperm and egg join, they grow into an embryo with two sets—one from the father's sperm and one from the mother's egg.

In SCNT, the egg cell's single set of chromosomes is removed. It is replaced by the nucleus from a somatic cell, which already contains two complete sets of chromosomes. So, in the resulting embryo, both sets of chromosomes come from the somatic cell.

Is cloning an organism the same as cloning a gene?

You may have heard about researchers cloning, or identifying, genes that are responsible for various medical conditions or traits. What's the difference?

When scientists clone an organism, they are making an exact genetic copy of the whole organism, as described above.

When scientists clone a gene, they isolate and make exact copies of just one of an organism's genes. Cloning a gene usually involves copying the DNA sequence of that gene into a smaller, more easily manipulated piece of DNA, such as a plasmid. This process makes it easier to study the function of the individual gene in the laboratory.

Reproductive Vs Therapeutic Cloning

What is therapeutic cloning?

Therapeutic cloning refers to the removal of a nucleus, which contains the genetic material, from virtually any cell of the body (a somatic cell) and its transfer by injection into an unfertilised egg from which the nucleus has also been removed. The newly reconstituted entity then starts dividing. After 4-5 days in culture, embryonic stem cells can then be removed and used to create many embryonic stem cells in culture. These embryonic stem cell ‘lines’ are genetically identical to the cell from which the DNA was originally removed. Therapeutic cloning is also known as somatic cell nuclear transfer (SNCT) as the term cloning is frequently misunderstood by the general public. The word ‘cloning’ more often conjures up thoughts and beliefs about reproductive cloning. Reproductive cloning is if a newly formed embryo, resulting from a therapeutic cloning procedure, were transferred into the womb of a woman, it could theoretically, develop into a fetus. This technique has been used to clone agricultural animals, endangered species and recently domestic pets and primates, but has not been proven in humans. The scientific community overwhelmingly rejects the use of therapeutic cloning for the purposes of human reproductive cloning. Reproductive cloning is illegal in Australia and in many other countries. While the procedure of therapeutic cloning employs aspects of cloning technology, researchers today are interested in therapeutic cloning as a means of deriving human embryonic stem cell lines for use in research and, ultimately, therapy. Therapeutic cloning has been legal in Australia since 2006 under the Prohibition of Human Cloning for Reproduction and the Regulation of Human Embryo Research Amendment Act 2006. Any Australian researchers wishing to use therapeutic cloning must apply to the National Health & Medical Research Council (NHMRC) for a licence.

What is special about therapeutic cloning?

The capacity of therapeutic cloning to re-program adult nuclei is extraordinary and unique. Cells of particular tissues generally express a characteristic set of

genes. Whether they are primitive stem cells, fully-differentiated (i.e. mature) cells, or something in between these extremes. Particularly for more mature cells, the tissue-specific patterns of gene expression are quite stable through many rounds of cell division. Upon transfer to an enucleated egg, the adult nucleus becomes re-programmed in the environment of the egg. That is, genes that were not used before (switched off) become reactivated. A poorly-understood process, re-programming involves dramatic changes in the pattern of genes which are active in the nucleus. Instead of the adult nucleus causing the egg to behave like an adult cell, the egg causes the nucleus to go backwards along a differentiation sequence, resulting in an embryonic type cell. As a result of therapeutic cloning, the previously unfertilised egg takes on the properties of a fertilised egg and begins the first stages of development into an embryo.

What is known about the embryos resulting from therapeutic cloning?

In broad terms, embryos arising from therapeutic cloning are the same as embryos from fertilisation of an egg by a sperm. In agricultural research, therapeutic cloning has been used to create embryos in the laboratory which have been transferred into animals and given rise to offspring. 'Dolly' the sheep was born as a result of this procedure. However, there are also differences between a normally fertilised egg and one produced by therapeutic cloning, which are not generally understood. In animal studies clones appear to have increased abnormality and decreased pregnancy rates. For example, despite being relatively young for a sheep, which can live to 11 or 12 years of age, Dolly died prematurely at the age of six years, showing signs of arthritis and lung infection. Other than the major ethical concerns, this is a fundamental reason why reproductive cloning should not be performed on humans. Research involving therapeutic cloning and its potential application .While the scientific community overwhelmingly rejects the use of THERAPEUTIC CLONING for reproductive cloning, it would provide an invaluable tool for basic research. As reported in Nature in November 2007 scientists successfully extracted stem cells from nonhuman cloned primate embryos. Although it is a highly significant achievement it must be considered that it took 304 eggs to produce two successful embryonic stem cell lines. In January 2008 a Californian company Stemagen reported it had successfully cloned a human blastocyst, an early stage embryo. The Stemagen embryos were the first to be made with human adult skin cells through therapeutic cloning, however they did not

attempt to produce stem cell lines, focusing their attention on extensive genetic tests to prove the identity of the cloned embryos. Researchers regard therapeutic cloning as an effective method for deriving human embryonic stem cells with specific characteristics, about which a great deal remains to be known and understood. The promise of therapeutic cloning is that it will be an effective way to derive embryonic stem cells which can then be used for the development of patient- and diseasespecific cell-based therapies as well as the production of stem cells with specific disease characteristics for research purposes. The use of a patient's own cells for tissue replacement through therapeutic cloning overcomes the problem of immune rejection that is a major complication of tissue transplantation today. Embryonic stem cells derived by nuclear transfer may, in the future, be used to treat diseases including diabetes, heart disease and Parkinson’s disease.

Reproductive Cloning

This type of cloning is done with the intent of making another organism. The clone will be an exact duplicate of the one that exists now. Reproductive cloning includes animals, plants, and humans.

Somatic Cell Nuclear Transfer, also referred to as SCNT, is the technique used for this type of cloning. A recipient egg's genetic material is extracted so that only an empty egg remains. A cell from the organism being cloned is taken and its nucleus is extracted. This nucleus is then implanted in the egg. The egg is then forced to divide, using a mild electric shock or chemicals, creating an embryo which will eventually be placed into the uterus of a surrogate mother.

As of today, this type of cloning has been used for research only, but its future uses are staggering. This type of cloning could be beneficial in making breeding specific animals simpler or in repopulating endangered species. It may also be used to create organisms with specific characteristics like genetically unique animals or drug-producing animals.

Ethical Issues of Cloning

Ever since the advent of cloning, there have been arguments for and against this process. A fundamental argument is that cloning is ethically wrong and various religious groups have rejected it saying that cloning is equivalent to 'playing God'. Here is a discussion about the ethical issues that have arisen concerned with cloning humans.

The rapid advancements in science and technology over the last couple of decades has meant that mankind is exploring newer frontiers and challenging long-held beliefs and notions. One such field is cloning. Creating exact copies or cloning human beings has always fired the human imagination. This desire has manifested itself in various art and entertainment depicting cloned humans. The successful cloning of Dolly in 1997 further fueled talk about the possibility of human cloning. Over the years, cloning has come to mean an artificial and identical genetic copy of an existing life form. 

To explain in a scientific way, cloning means replacing the egg nucleus of an organism with the donor's nucleus. This nucleus contains unique genes of the donor. The procedure involves removing the nucleus of a somatic cell and inserting it into an enucleated or unfertilized egg cell. Unlike natural reproduction, wherein the egg contains a combination of genetic material, this egg which grows into an embryo contains only the donor's gene.

Theoretically, this might seem fairly straightforward. However, a high failure rate along with prevalence of high deformity and disability rates in cloned animals, strongly suggests cloning might not be applicable to humans.

The Ethical Issues

Religious Belief and Control:

Cloning goes against the basic belief of certain religions that only God has created life and its various forms in nature. Humans cannot act as God. Even when genetically identical twins are born, their embryo splits spontaneously or randomly to give a new unique genetic combination. Cloning involves a controlled split of the embryo to produce a tailor-made genetic makeup. Ethically, it is wrong for any human to have control over the genetic makeup of any other individual. More so, the cloned individual would be generated for specific purposes. This in essence is wrong wherein the purpose of an individual's life should be more than just satisfying someone else's needs.

Relationships and Individuality

Cloning creates a new human, yet strips him off his individuality. A man, along with his clone can never be dignified as a single identity. The uniqueness attributed to humans from God might be at stake. The replication of an individual is a major blow to his most distinct feature - his identity. Another fact is that we are unsure how the cloned individual might react and behave with regards to his family and parents. Furthermore, if the cloned individual is cloned from his grandparents and not his parents, would he/she be considered a sibling? How would he/she react? How would the parents and family regard the cloned individual? When we are unsure about the implications or consequences of such situations, it is ethically wrong to subject any individual to such tests as fellow human beings.

Failure Rate

Physicians and doctors have a moral obligation to ensure and translate the safety of any medical procedure to his/her patients. As of now, no one can guarantee that the child born due to cloning would be a healthy one. As indicated earlier, the high failure rate in cloning mammals and other species is completely unacceptable when it comes to cloning humans. Moreover, in case of a failed cloning attempt, putting down mammals or other species in itself is distressing. Translating the same in case of human clones is ethically and medically unjustifiable, as well as criminal.

Legal and Other Issues

Besides the above mentioned issues, there are other issues which may seem technical as of now, but can arise out of lack of knowledge or unforeseeable circumstances.

Altering Gene PoolIf cloning becomes widespread, the genetic diversity of humans will go down. This would result in the decrease in immunity of humans against diseases. Thus making humans susceptible to epidemics and unknown diseases. Some advocate human cloning as ethically unacceptable because it is seen as a threat to the

entire human evolution. Though this issue is slightly hypothetical, it still can pose a potential threat to all humanity. Along with reducing generic diversity, there are risks of transmitting degenerative diseases from the donor human to the clone. Trans-genetic manipulation, where genetic material from one species is artificially inserted into another species, if applied to humans, would lead to transfer of diseases from other species. Thus, large-scale cloning might prove to be a serious blow to the entire human race in future. 

Illegal Cloning and ClonesCloning could have legal implications as well. A cloned child having multiple donors might complicate parental right issues as well as inheritance and marital eligibility issues. Another view held by many experts, suggests that there is a possibility of clones being developed without the concerned individual's consent. This will definitely create legal issues not to mention violation of medical as well as moral ethics. Many people are also concerned that clones would be produced with a specific need and purpose in mind and such cloned individuals would be traded or sold, amounting to human trafficking which is illegal.

At the other end of spectrum are some experts who are of the opinion that the embryo does not require any particular moral consideration. They say that, at the stage when an embryo is cloned, it is just a bunch of cells that contain DNA, which are not very different from the millions of skin cells that we shed every day. The embryonic cells at that stage cannot be considered equivalent to a human being because it does not have thoughts, self-awareness, memory, awareness of its environment, sensory organs, internal organs, legs, arms, and so on. They think that the embryo attains human identity or individuality much later during gestation, perhaps at the point when the brain develops so that it becomes aware of itself.

In view of the highly debatable aspects about cloning and weighing in on the pros and cons of this process, UNESCO passed a non-binding United Nations Declaration on Human Cloning, in March 2005, which states: Practices which are contrary to human dignity, such as reproductive cloning of human beings, shall not be permitted. In the United States there are no federal laws that ban cloning completely, yet 13 states have banned reproductive cloning. Although many countries have banned cloning, many countries allow therapeutic cloning,

a system in which the stem cells are extracted from the pre-embryo, with the intention of generating a whole organ or tissue, so that it can be transplanted back into the person who gave the DNA.

Since human cloning raises some serious concerns, it would be highly irresponsible to pursue this method, without giving it a serious thought. New issues are bound to crop up with advances in this field, and only time can decide its fate. Until the benefits are discussed by society to outweigh the harm, it would be inappropriate to participate in cloning of humans.