找两篇英语小短文,关于克隆的

找两篇英语小短文,关于克隆的
找两篇英语小短文,关于克隆的

找两篇英语小短文,关于克隆的
Why Clone?
Research advances over the past decade have told us that,with a little work,we humans can clone just about anything we want,from frogs to monkeys and probably even ourselves!
So,we can clone things,but why would we want to?Let's look at some of the reasons people give to justify cloning.
1.Cloning for medical purposes
Cloning for medical purposes
Of all the reasons,cloning for medical purposes has the most potential to benefit large numbers of people.How might cloning be used in medicine?
* Cloning animal models of disease
Much of what researchers learn about human disease comes from studying animal models such as mice.Often,animal models are genetically engineered to carry disease-causing mutations in their genes.Creating these transgenic animals is a time-intensive process that requires trial-and-error and several generations of breeding.Cloning technologies might reduce the time needed to make a transgenic animal model,and the result would be a population of genetically identical animals for study.
* Cloning stem cells for research
Stem cells are the body's building blocks,responsible for developing,maintaining and repairing the body throughout life.As a result,they might be used to repair damaged or diseased organs and tissues.Researchers are currently looking toward cloning as a way to create genetically defined human stem cells for research and medical purposes.
* "Pharming" for drug production
Farm animals such as cows,sheep and goats are currently being genetically engineered to produce drugs or proteins that are useful in medicine.Just like creating animal models of disease,cloning might be a faster way to produce large herds of genetically engineered animals.
2.Reviving Endangered or Extinct Species
Dinosaur
Have you seen Jurassic Park?In this feature film,scientists use DNA preserved for tens of millions of years to clone dinosaurs.They find trouble,however,when they realize that the cloned creatures are smarter and fiercer than expected.
Could we really clone dinosaurs?
In theory?Yes.What would you need to do this?
* A well-preserved source of DNA from the extinct dinosaur,and
* A closely related species,currently living,that could serve as a surrogate mother
In reality?Probably not.It's not likely that dinosaur DNA could survive undamaged for such a long time.However,scientists have tried to clone species that became extinct more recently,using DNA from well-preserved tissue samples.
3.Reproducing a Deceased Pet
Pet
No joke!If you really wanted to,and if you had enough money,you could clone your beloved family cat.At least one biotechnology company in the United States offers cat cloning services for the privileged and bereaved,and they are now working to clone dogs.But don't assume that your cloned kitty will be exactly the same as the one you know and love.
4.Cloning Humans?
Newborn
To clone or not to clone:that is the question.The prospect of cloning humans is highly controversial and raises a number of ethical,legal and social challenges that need to be considered.
Why would anyone want to clone humans?Some reasons include:
* To help infertile couples have children
* To replace a deceased child
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Defining Human Cloning
When speaking of human cloning,what is meant?Different groups and organizations define it differently.To use a specific definition,the American Medical Association (AMA) defined cloning as 鈥渢he production of genetically identical organisms via somatic cell nuclear transfer.鈥楽omatic cell nuclear transfer鈥 refers to the process which the nucleus of a somatic cell of an existing organism is transferred into an oocyte from which the nucleus has been removed鈥 (Council on Ethical and Judicial Affairs 1).In other words,cloning is the method of produce a baby that has the same genes as its parent.You take an egg and remove its nucleus,which contains the DNA/genes.Then you take the DNA from an adult cell and insert it into the egg,either by fusing the adult cell with the enucleated egg,or by a sophisticated nuclear transfer.You then stimulate the reconstructed egg electrically or chemically and try to make it start to divide and become an embryo.You then use the same process to implant the egg into a surrogate mother that you would use with artificial insemination.(Eibert)
However,many groups have used a broader definition of cloning.They include the production of tissues and organs through growing cells or tissues in cultures along with the actual producing of embryos to be born.This is done with the use of stem cells.When an egg is fertilized and begins to divide,the cells are all alike.As the cells divide,certain cells differentiate and become the stem cells that produce certain tissue and then organs.Research in this very active.There is still much for scientists to learn about cell differentiation and how it works.To a clone an organ,a stem cell must be produced and then used to a clone that specific organ.For the sake of this paper,both definitions will be used in order to cover all opinions.
One must understand that cloning does not produce an exact copy of the person being cloned.What cloning does,is that it copies the DNA/genes of the person and creates a duplicate genetically.The person will not be a Xerox copy.He or she will grow up in a different environment than the clone,with different experiences and different opportunities.Genetics does not wholly define a person and the personality.
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a bit long.you can make some adjustment anyway~