by Jonah Turk and Ben Kater
What is cloning?
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| The process of Embryo Twinning |
that are exact copies, down to
a genetic level.
Every single piece of their DNA
is exactly identical. There are three different types of artificial cloning: gene cloning, reproductive cloning, and therapeutic cloning. Gene cloning, as the name suggests, produces copies of genes or segments of DNA. Reproductive cloning produces full copies of animals. Therapeutic cloning produces stem cells from an embryo. These stem cells are used for experiments designed to create tissues that would replace injured or diseased tissues.
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| An Example of SCNT in Sheep |
Cloning also occurs naturally. In nature, some plants and single-celled organisms produce genetically identical offspring asexually. In asexual reproduction, new individuals are generated from copies of single cells from parent organisms. Also, in humans and other mammals, natural clones are referred to as identical twins. Identical twins are produced when a fertilized egg splits into two, which creates two separate embryos that carry nearly identical DNA.
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| An Example Of Cloning a Plant From a Cutting |
Cloning plants has been around
since the beginning of agriculture.
Ancient farmers discovered that a
cutting from a tree could grow a
new plant, unaware that the new plant
has identical genetics as the original tree.
People have been cloning plants for thousands of years as an agricultural
technique to facilitate farming. We now
know how and why these natural
phenomenons occur and we can
replicate them in a controlled
environment to benefit from cloning.
How Are Genes Cloned in Gene Cloning?
Researchers use techniques that allow them to make copies of genes that the researchers would like to study. The researchers must insert the foreign DNA, or a gene from another organism, into the genes of a carrier called a vector. Vectors include bacteria, yeast cells, viruses, and plasmids, which are small DNA circles which bacteria carry. After the foreign DNA is inserted, the vector is put in lab conditions that prompt it to multiply, thereby allowing the gene to multiply as well.
How Are Animals Cloned in Reproductive Cloning?
In reproductive cloning, researchers start by removing a mature somatic cell from the animal they wish to clone. The next step in the procedure is to transfer the DNA of the previously removed somatic cell into an oocyte. This oocyte, or egg cell, has previously had its own DNA-containing nucleus removed. There are two different ways to add the somatic cell's DNA to the empty egg. In the first, they use a needle to remove the DNA of the somatic cell and inject it into the empty egg. In the second method, researchers will use an electric current, which combines the entire somatic cell with the empty egg. In both cases, researchers will let the egg develop into an early-stage embryo while inside the test-tube. After this, the embryo is implanted into an adult female animal's womb. Eventually, the adult female animal will give birth to a clone, which has the same genetic make-up as the animal which gave its cells. A surrogate mother may be required, so as to allow the clone to develop.
know how and why these natural
phenomenons occur and we can
replicate them in a controlled
environment to benefit from cloning.
How Are Genes Cloned in Gene Cloning?
Researchers use techniques that allow them to make copies of genes that the researchers would like to study. The researchers must insert the foreign DNA, or a gene from another organism, into the genes of a carrier called a vector. Vectors include bacteria, yeast cells, viruses, and plasmids, which are small DNA circles which bacteria carry. After the foreign DNA is inserted, the vector is put in lab conditions that prompt it to multiply, thereby allowing the gene to multiply as well.
How Are Animals Cloned in Reproductive Cloning?
In reproductive cloning, researchers start by removing a mature somatic cell from the animal they wish to clone. The next step in the procedure is to transfer the DNA of the previously removed somatic cell into an oocyte. This oocyte, or egg cell, has previously had its own DNA-containing nucleus removed. There are two different ways to add the somatic cell's DNA to the empty egg. In the first, they use a needle to remove the DNA of the somatic cell and inject it into the empty egg. In the second method, researchers will use an electric current, which combines the entire somatic cell with the empty egg. In both cases, researchers will let the egg develop into an early-stage embryo while inside the test-tube. After this, the embryo is implanted into an adult female animal's womb. Eventually, the adult female animal will give birth to a clone, which has the same genetic make-up as the animal which gave its cells. A surrogate mother may be required, so as to allow the clone to develop.
What Animals Have Been Cloned?
In 1979, scientists produced the first genetically identical mice. They achieved this by splitting embryos in the test tube and then placed them in adult female mice's wombs. Not long after, the first genetically identical sheep, cows, and chickens were produced. This was achieved by transferring a nucleus from an early embryo's cell into an empty egg.
In 1996, scientists produced the first clone created from a somatic cell. After 276 attempts, Dolly the sheep was finally produced by Scottish researchers.
In 1998, Japanese scientists cloned eight calves, four of which survived.
Besides cattle and sheep, mammals that have been cloned from somatic cells are:
cat, deer, dog, horse, mule, ox, rabbit, and rat.
Similarly to the mice, a rhesus monkey was produced by splitting embryos.
Human Cloning
There have been multiple claims of human cloning, all of which were not able to be backed up by scientific evidence and therefore are considered fiction.
In 1998, South Korean scientists claimed to have successfully cloned a human embryo. However, they also stated that the experiment was interrupted very early when they found the "clone" to be nothing more than a group of four cells.
In 2002, Clonaid, part of a religion called Raëlism, which believes that aliens created humans, announced the birth of a human clone, a female named Eve. However, Clonaid never provided any evidence.
In 2004, a group led by Woo-Suk Hwang of Seoul National University published an article in the science paper Science in which he claimed to have cloned a human embryo in a test tube. However, this was later found to be false and the article was later retracted from the paper.
Cloning in humans and other primates is difficult in comparison to other mammals. The spindle proteins, which are located near the chromosomes in primate eggs, are essential to cell division. However, removing the eggs nucleus also removes the spindle proteins with it.
Controversy Behind Cloning: Pros and Cons of Cloning
Pros:
- Cloning plants could be used to produce a greater surplus.
- Cloning plants can help produce plants that are more disease resistant.
- Cloned plants are much more consistent in their growth patterns and can save farmers lots of money.
- Cloning food-producing animals can produce superior foods and address the issue of world hunger.
- Cloning could help to save animals on the brink of extinction.
- Vital human organs needed to be replaced in patients can be cloned to save lives.
Cons:
- Efforts to genetically engineer or fully clone plant and animal species could result in a lack of needed DNA diversity.
- Scientists can't predict potential development of viruses or other agents of destruction to which a cloned species might need to react in the future.
- Also, cloning can limit genetic variation in the future.
- It is more expensive to clone animals than to reproduce them naturally.
- Many believe that cloning is "playing God" and therefore refuse to support it.
History
- 1964: F.E. Stewart of Cornell University successfully grew an entire carrot plant out of a single carrot root cell, proving cloning is possible.
- 1983: Kary Mullis invented the polymerase chain reaction which allows rapid replication of designated DNA fragments. This technology greatly facilitated every aspect of molecular biology.
- 1984: Danish scientist Steen Willadsen cloned a sheep from embryonic cells, using a method called nuclear transfer. This was the first confirmed case of mammalian cloning.
- 1986: Willadsen cloned a cow using cells extracted from one-week old embryos.
- 1990: Human genome project begins as an international effort to sequence the entire genetic makeup of humans.
- 1996: Ian Wilmut and Keith Campbell successfully clone the first animal from adult cells. Dolly the sheep is born on July 5, 1996. This proved that cloning from adult cells was possible.
- 1997: President Bill Clinton signed a 5-year ban on using government funds for human cloning.
- 2001: Noah, a bull gaur was cloned by scientists at Advanced Cell Technology Inc. This marks the first time an endangered species has been cloned.
- 2014: For the first time, scientist have turned the skin cells of an old man into stem cells. These can be used for medical transplants in the future, using a technique called the Roslin technique. This same technique was used to clone Dolly the sheep.
