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DNA Cloning of Mammals: Not Always Perfect Twins

Updated on April 13, 2022
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Angela, an animal lover, has a passion for learning and understanding God's creatures. As a born teacher, she enjoys sharing her knowledge.


What Is Cloning?

Cloning is the development of two identical organisms. It has occurred in humans as long as identical twins have been born. Only in the past century have scientists begun to discover ways to create cloned organisms artificially, which, of course, has arisen a lot of great debate on whether cloning should be legal.

The first kind of cloning scientists used on mammals was artificial embryo twinning. It is a very low-tech procedure to create twins that have been around for decades. This technology soon caused scientists to begin researching other ways to create clones, and soon came across somatic cell nuclear transfer, where they started to make clones of adult organisms. They did this in the case of Dolly, the sheep. In 1997, Dolly was the first organism to be cloned through somatic cell nuclear transfer, meaning Dolly is genetically identical to her 'donor mother.'

Artificial Embryo Twinning

Before Dolly, there was an artificial embryo twinning. To understand how artificial twinning occurs, it is best to know how identical twins develop. Identical twins differ from fraternal twins because they come from one sperm and one egg; therefore, identical twins have the same DNA, making them genetically identical, which occurs soon after an egg and a sperm meet when the original is still a zygote. The zygote will then begin to replicate. In single childbirth, the cells replicated will stay attached and grow until a full-grown fetus is born. In the case of identical twins, when the zygote forms a duplicate cell, they split into two. Then each cell will duplicate and build on each other just as a single childbirth cell would, except, in this case, there are two genetically identical embryos. The identical twins are essentially clones of one another.

Artificial embryo twinning happens very similarly; except instead of splitting while the cell is in the mother's womb, the zygote is divided inside a petri dish by a scientist. The newly divided zygotes will then be implanted into a surrogate mother who will give birth to two babies.



Somatic Cell Nuclear Transfer

The most significant difference between somatic cell nuclear transfer and artificial embryo twinning is where they get their DNA. A clone developed from artificial embryo twinning takes its chromosomes from a mother and a father. A clone from the somatic cell nuclear transfer gets all its chromosomes from one organism, making it a replica of its 'donor parent.' Somatic cell nuclear transfer is the same as reproductive cloning. A scientist accomplishes reproductive cloning by taking a somatic cell from an adult. A somatic cell is any cell that is not an egg or sperm. This is because an egg or sperm only has half the amount of chromosomes as a somatic cell, which is only half the amount of chromosomes any given species needs to develop.

Scientists will then take the nucleus out of the somatic cell and place it into an egg with its nucleus removed. They do this because the nucleus is much like the brain of the cell. It contains all chromosomes needed in DNA. The DNA tells the cell how to form, what the person will look like, how they will develop, and all other pertinent information. By replacing the nucleus from an egg cell with a nucleus that has all the chromosomes, the egg acts like a fertilized egg, forming a zygote. It will then develop with the exact information as the 'donor parent,' which causes the new cell to become the clone of the 'donor parent,' making them genetically identical.

This new cell will then be implanted into a surrogate mother who will carry the baby until delivery. Unfortunately, less than 10 percent of all implanted somatic cell transfers survive. Some species are also more resistant to being cloned than others, as scientists have had more success with certain animals.


The Cloning of Animals

The first thing to understand about cloning animals is that there is much more that makes up a creature than just genetic makeup. If you have ever met identical twins, you know that two people with identical DNA can be very different. They can have other interests, different personalities, different dreams, etc. They are not the same person. Let's say your sweet cat is getting old, and you are thrilled when you discover that you can have him cloned for a fee. Just because they will be genetically the same, they may not have the same temperament since genes only take us so far.

As you may have heard of the nature versus nurture theory, nature would be the genetic makeup of the new cat, but nurture would be all the other factors, from what its surrogate mother ate to how it was treated as a young kitten. There are so many outside factors that could change the personality of your newly cloned cat that may cause it to have a very different personality than the cat you loved before, which is why many people are opposed to cloning.

Let's take this idea a step further. A couple is traumatized by the death of their son, Timmy. They learn that there is a doctor who will clone children. They choose to have Timmy cloned. She carries this new child to term. What if she ate different foods or carried this child during a different season. How will these changes affect the growing fetus? Then the child is born. He looks just like Timmy, but he doesn't like baseball or sports. He prefers more artistic pursuits. Will the parents try to mold the new Timmy to be like the old one? How will this affect the new Timmy's perception of himself? Humans are emotional beings. There are so many factors involved in cloning humans that could be detrimental to the emotional health of the clone.

Another thing to note aside from just nature versus nurture is that the nucleus is only a portion of the cell. There is also the cytoplasm, which contains mitochondria. Mitochondria may play a role in how we age, although its effect on the rest of our growth is unknown. The rate of failure for cloning is relatively high due to premature death deformity, among other things, which shows that the clones are not as identical to their 'donor parents' as previously thought.


CC and Rainbow

Being not as identical as previously thought is very much the case for two cats, Rainbow and CC. By just looking at them, you would have no idea that CC, which stands for carbon copy, is the clone of Rainbow. Rainbow is a calico cat, whereas CC is a gray tabby with no orange color.

CC was born December 22, 2001, and was the first cloned cat. After CC was born, Dr. Leslie Lyons wanted to test their DNA to prove they were, in fact, clones, despite their difference in appearance. Therefore, Lyons took a DNA sample from both cats and sent it to a lab for a blind test, where the testers had no idea that the DNA samples came from two separate cats. The test results came back that the DNA was precisely the same.

So why the difference? Shortly put--environmental factors. Cats have a gene in their skin that either activates orange coloring or does not activate orange coloring. Rainbow's genes in her skin had randomly activated genes for this coloring, whereas not a single gene in CC's skin was activated for this coloring. Also, white spotting is very random in cats, which means that the white spotting is different despite their exact DNA.

Also, the two cats acted very differently, which was most likely because CC was handled a lot as a kitten early on. Rainbow is more reserved, while CC, as you would expect, is more curious and friendly than Rainbow.

On a side note, CC did become a mother, which they allowed to happen to see if a cloned cat could reproduce, which proved that they could. The scientists considered CC to be a very good mother.

Cloning Extinct Animals Quiz

Should scientists clone extinct animals?

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Cloning Extinct Animals

Though many people will agree that cloning humans are not a good idea, they view the cloning of extinct animals as a way to learn a lot about our planet's history. We can reestablish creatures that died off many years ago, as long as we have DNA and a surrogate mother to develop the creature in. Theoretically, this is a great step in technology and biology. We can replenish endangered animals. We can discover why dinosaurs became extinct. We can find out what the saber-tooth cat looked like.

Although we need to stop and ask, is this a good idea? There are reasons certain animals became extinct. Reintroducing creatures that have become extinct into the wild could severely disrupt our ecosystem. What if the saber-tooth cat eats other wild cats and kills off the last of the lions? Or what if the dinosaur created chases humans killing off entire communities with a Jurassic Park-like epidemic? There are way too many unknowns about reintroducing extinct animals into our world.

Although there is a lot of good that cloning can result in, there are many things scientists need to consider before they begin cloning things just because they can. We need to consider the emotional impact cloning may have on the clone itself and the people around them. We also need to keep in mind the impact that cloning extinct or even endangered animals may have on our ecosystem. Although cloning can be used in healthy, profitable ways, anytime cloning is considered, the ramifications of bringing the clone into earth need to be weighed before proceeding.

Human Cloning Video

© 2012 Angela Michelle Schultz


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