When we speak of cloning, we typically think of organism cloning, but there are actually three different types of cloning.

Molecular cloning focuses on making identical copies of DNA molecules. This type of cloning is also called gene cloning.

Organism cloning involves making an identical copy of an entire organism. This type of cloning is also called reproductive cloning.

Therapeutic cloning involves the cloning of human embryos for the production of Stem Cells. The embryos are eventually destroyed in this process.

[top]Reproductive Cloning Techniques

Cloning techniques are laboratory processes used to produce offspring that are genetically identical to the donor parent.

Clones of adult animals are created by a process called somatic cell nuclear transfer.

What is cloning? What are cloning techniques? Cloning refers to the development of offspring that are genetically identical to their parent. Animals which reproduce sexually are examples of clones that are produced naturally.

Thanks to advances in genetics however, cloning can also occur artificially by using certain cloning techniques. Cloning techniques are laboratory processes used to produce offspring that are genetically identical to the donor parent.

Clones of adult animals are created by a process called somatic cell nuclear transfer. There are two variations of this method. They are the Roslin Technique and the Honolulu Technique. It is important to note that in all of these techniques the resulting offspring will be genetically identical to the donor and not the surrogate, unless the donated nucleus is taken from a somatic cell of the surrogate.

[top]Cloning Techniques

Somatic Cell Nuclear Transfer

The term somatic cell nuclear transfer refers to the transfer of the nucleus from a somatic cell to an egg cell. A somatic cell is any cell of the body other than a germ (reproductive) cell. An example of a somatic cell would be a blood cell, heart cell, skin cell, etc..

In this process, the nucleus of a somatic cell is removed and inserted into an unfertilized egg that has had its nucleus removed. The egg with its donated nucleus is then nurtured and divides until it becomes an embryo. The embryo is then placed inside a surrogate mother and develops inside the surrogate.
The Roslin Technique

The Roslin Technique is a variation of somatic cell nuclear transfer that was developed by researchers at the Roslin Institute. The researchers used this method to create Dolly.

In this process, somatic cells (with nuclei in tact) are allowed to grow and divide and are then deprived of nutrients to induce the cells into a suspended or dormant stage. An egg cell that has had its nucleus removed is then placed in close proximity to a somatic cell and both cells are shocked with an electrical pulse. The cells fuse and the egg is allow to develop into an embryo. The embryo is then implanted into a surrogate.
The Honolulu Technique

The Honululu Technique was developed by Dr. Teruhiko Wakayama at the University of Hawaii. In this method, the nucleus from a somatic cell is removed and injected into an egg that has had its nucleus removed. The egg is bathed in a chemical solution and cultured. The developing embryo is then implanted into a surrogate and allowed to develop.

[top]Cloned Animals

Scientists have been successful in cloning a number of different animals.

How do you spell breakthrough? D-O-L-L-Y
Scientists have succeeded in cloning an adult mammal.
And Dolly doesn't have a daddy!

What if humans could fly? What if we could live for two hundred years? What if there were several other people out there exactly like us? Wait... this was supposed to be a litany of distant possibilities. We shuddered last week when we saw the headlines,Dolly is a clone! And no, we're not talking about the tabloid headlines about Dolly Parton. Scientists have succeeded in cloning an adult mammal to produce a sheep named Dolly. That means that Dolly is genetically identical to her mother! And Dolly doesn't have a daddy! Wow! Where could this lead?
In a nutshell, scientists extracted some nuclei from the udder cells of an adult sheep and inserted the nuclei into ova. The original nuclei in the ova had been removed. Nuclei contain DNA, (deoxyribonucleic acid, for the technically inclined) the basic "building blocks" of life through which genetic information is passed. On a simple level, DNA allows the transmission of your grandfather's distinct nose or your mother's beautiful dimples. When the nuclei were transferred to the ova, the "adult" nuclei acted as if they were "baby" nuclei and began to divide. The research team then implanted the dividing egg into the "mother" who had produced the original egg and a little while later, an exact genetic copy-- a clone -- was born! Hmmm, we used to think that cloning was the stuff of science fiction and late night horror movies.
If these events weren't shocking enough, another research group at Portland's Oregon Health Sciences University, using a similar technique, announced that they had had success in cloning primates. Unlike Dolly, whose donor cells came from an adult, the cloning of the primates involved using embryos. Scientists are divided on the significance of this work, since many labs have used embryos to produce clones for at least the last decade. Even so, just a little too close to home, don't you think? To cut to the chase, this is a big step, and we do mean BIG! Theoretically, it is possible for scientists to unlock the mechanisms for cloning humans, which leads us to all kinds of implications. Would you want to be cloned? Imagine, you have a doctor's appointment, you give just a wee bit of blood, and a year later you find out that you have a genetic double. While I'm exaggerating a bit, the implications are enormous.

First Dolly and Now Millie
Scientists have successfully produced cloned transgenic goats.

First Dolly and now Millie. Millie is a transgenic goat. Her milk contains a protein that could be extracted to make a drug for coronary bypass patients. The protein, called anti-thrombin III (AT III), is now in human clinical trials.

To produce a transgenic goat, researchers must follow several steps. First, the gene that produces AT III is sequenced, and scientists build a synthetic gene and make many copies.
The synthetic gene is then attached to the gene for casein, which acts as a promoter gene. This ensemble is then injected into a newly fertilized egg. During the first few critical cell divisions, the gene may become attached to the goat's DNA. If successful, the new gene is now a transgene which will become incorporated into all cells during subsequent divisions.
The embryo is then transferred to a surrogate mother. If the embryo turns out to be female, the AT III protein will be produced in her milk.
Based on this traditional method, approximately 50% of the offspring of an AT III goat would have the gene. Scientists then took this a step further. With the advent of refined cloning techniques in the past two years, researchers believed they could increase their efficiency rate by not only producing transgenic goats but also cloned transgenic goats.
Unlike Dolly, who was produced from an adult cell, the researchers used fibroblast cells from a 30-day old female goat fetus. After being grown in an incubator with media that contained the gene for AT III, the cells went through a process called electroporation. Electroporation allowed the cells to become porous and made it possible for the AT III gene to enter the cell's nucleus. These cells were fused with an egg whose nucleus had been removed. The cloned embryos were then implanted into a surrogate. The final products were three identical female transgenic goats that produced the AT III protein.

Cloning Clones
Researchers have developed a way to create multi-generations of identical mice.

An international research team in Hawaii has developed a way to clone mice from adult cells using a process called the Honolulu Technique. This process, once thought to be impossible, has allowed researchers to successfully clone five generations of healthy mice.

The Honolulu Technique involves removing adult mouse nucleic cells from the donor and micro-injecting them into an egg from which the original nucleus has been removed. The egg is treated with special chemicals and is eventually implanted into a surrogate mouse. The resulting offspring is genetically identical to the donor.

This process differs from the technique used to produce Dolly in that there is no fusion of cells involved. With Dolly, adult sheep cells were fused together before being implanted in the sheep which originally donated the egg. The Honolulu Technique has a much higher success rate. Since mice have a short reproductive cycle, scientists stress the importance of this newfound ability to clone them using the Honolulu Technique.

Scientists are excited about the possible ways in which this technique can be used in researching, treating, and conquering human diseases such as AIDS, cancer, multiple sclerosis, and diabetes. By applying the Honolulu Technique to other animals, like sheep for example, researchers may gain a better understanding of the cellular and molecular mechanisms behind these and other diseases.

The Honolulu Technique could also be used to genetically alter animals for the production of human transplant organs. Researchers stress that this breakthrough is not intended for the cloning of humans, but for the ability to arm ourselves with the tools necessary to fight disease.

[top]Cloning Problems

What are therisks of cloning? One of the main concerns as it relates to human cloning is that the current processes used in animal cloning are only successful a very small percentage of the time.

Another concern is that the cloned animals that do survive tend to have various health problems and shorter life spans.

Scientist have not yet figured out why these problems occur and there is no reason to think that these same problems wouldn't happen in human cloning.

[top]Cloning and Ethics

Should humans be cloned? A major objection to cloning for research is that cloned embryos are produced and ultimately destroyed. For more information on cloning and ethics, see:

Biological Ethics: Cloning Revisited
Cloning still raises very serious ethical issues.

In How do you spell breakthrough? D-O-L-L-Y, I discussed cloning. Much has transpired since this initial article, but challenging assumptions and ethical implications of the cloning process remain. Let's review how scientists created a clone of an adult mammal, aptly named Dolly.
Simply put, scientists extracted nuclei from the udder cells of an adult sheep and inserted the nuclei into ova from which the original nuclei had been removed. Cell nuclei contain deoxyribonucleic acid (DNA), aka, the basic "building blocks" of life through which genetic information is passed. DNA allows the transmission of characteristics such as your grandmother's distinct nose. When the nuclei were transferred to the ova, the "adult" nuclei acted as if they were "baby" nuclei and began to divide. The scientists then implanted the dividing egg into the "mother" who had produced the original egg and a few months later, an exact genetic copy-- a clone -- was born!
This was fascinating for two reasons: (1) it was the first time an adult mammal had been cloned, and (2) it raises the possibility that we may one day be able to clone humans. Obviously, this raises many ethical issues. For example:
Would it be ethical to clone a human without a brain for use in organ transplants?
Would it be ethical to use clones for scientific research? These questions raise issues that both the scientific community and the public must address if the technology for cloning humans becomes feasible. What do you think? Should we clone humans? More importantly, what are the boundaries for the "practice" of science and the "implications" of science?