FREE ESSAY ON CLONING_WHAT_IS_IT?

CLONING_WHAT_IS_IT?

Cloning
What is Cloning?
Cloning is the production of one or more individual plants or animals that are
genetically identical to another plant or animal. Nature itself is the greatest cloning
agent. In about one of every 75 human conceptions, the fertilized ovum splits for some
unknown reason and produces monozygotic (identical) twins. Each has a genetic makeup
identical to the other. 
Two very different procedures have been referred to as cloning: 
? Embryo cloning has been successfully carried out for years on many species of animals.
Some limited experimentation has been done on human embryos. 
? Adult DNA cloning has been used to clone a sheep, but was not tried on humans until
December 1998.
How is Embryo Cloning is Done?
Human embryo cloning starts with a standard in vitro fertilisation procedure. Sperm and
an egg cell are mixed together on a glass dish. After conception, the zygote (fertilised
egg) is allowed to develop into a blastula (a hollow mass of cells). The zygote divides
first into two cells, then four, then eight... A chemical is added to the dish to remove
the zona pellucida covering. This material provides nutrients to the cells to promote
cell division. With the covering removed, the blastula is divided into individual cells,
which are deposited on individual dishes. They are then coated with an artificial zona
pellucida and allowed to divide and develop. The experiment by Sillman showed that the
best results could be obtained by interrupting the zygote at the two-cell stage. Many of
these pairs of zygotes were able to develop to the 32-cell stage, but no further. They
might well have had the potential to develop further and even mature into a viable
foetus, except that the original ovum was defective and would have died anyway. For
ethical reasons, the researchers selected embryos which had no possibility of ever
maturing into foetuses, and thus into newborn babies.
How is Adult DNA Cloning Done?
With the exception of the sperm and egg, every cell in the body contains all of the
genetic material in its DNA to theoretically create an exact clone of the original body.
But cells have been biochemically programmed to perform limited functions. The other
functions are turned off. Most scientists had believed that such differentiated cells
could not be reprogrammed to be capable of behaving as a fertilized egg. 
In the case of the sheep Dolly", a cell was taken from mammary tissue of a mature 6 year
old sheep while its DNA was in a dormant state. It was fused with a sheep ovum which had
had its nucleus removed. The fertilised cell was then stimulated with an electric pulse.
Out of 277 attempts at cell fusion, only 29 began to divide. These were all implanted in
ewes. 13 became pregnant but only one lamb, Dolly, was born.
History of Cloning
Cloning has had a fairly long history:
? The first successful cloning experiment involved a leopard frog. It took place in, 1952
with group of scientist from the Institute for Cancer Research in Philadelphia. To clone
the frog they used an embryonic frog cell nucleus 
? In 1962, John Gurdon of Cambridge University cloned a toad that survive threw adulthood
and was able to reproduce. He was also the first to take a nucleus from a fully contrast
tadpole intestinal cell and cloned toads(Robertson)
? In 1981, Steen Willadsen was the first to clone an artificial chimera. He did this by
mixing a sheep and a goat getting the result of a geep. It had the body shape and the
head of a goat, and a dappled coat which had large patches of sheep's wool
? In 1984, Willadsen cloned the first verifiable mammal, using embryonic nuclei
transplant into an unfertilised sheep egg
? In 1986, when Willadsen worked for Texas bioengineering company, he produced the first
cloned calves from cattle by using the embryonic nuclei. The cloned cattle that were
produced were super-elite, high production dairy cows and bulls who had a high breeding
rate 
? In 1987, James Robl of the University of Massachusetts was the first to clone rabbits
also using embryonic nuclei
Going by these past events, who can say when we will be able to clone human organs or
complete biocopies of human beings by using just the nuclei taken from a skin sample.
Advantages and Disadvantages
Cloning has many more advantages than disadvantages. Through cloning, you could help
thousands of people and animals. Some of the ways that people could be helped are:
? Totally reduce organ donor lists
? Bring back endangered species
? Allows dairy products to be enriched. For example, cloning provides scientists a method
to engineer cows to produce certain medicines or enzymes in there milk
? Cure life threatening diseases and repair cosmetic defects
? Produce new, fresh tissue for burn victims, or new nerve tissue for burns or back
injuries
? Produce new heart cells for people with bad hearts
There are also disadvantages of cloning, they are:
? Taking God's work into our own hands
? Have an impact on the decline in genetic variety
? If we ever lost the ability to clone, we would have to resort to natural reproduction,
causing us to inbreed, which could be disastrous
? If everyone had the same genetic information, one disease could wipe out a whole
population
Bibliography
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