Englischverständnis für fortgeschrittene Anfänger – Buch 1

now?
    6. Name two things that could be found in a codex.
    7. During human sacrifice, how was a person killed?
    8. In what area did the Maya live?
    9. Why did you have to be brave to look into a mirror in the Maya culture?
    10. True or false? – The Spanish killed the Mayas.
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Cloning
     

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    Imagine a world where parents can recreate a child who died. Or, where governments grow armies of soldiers. A world where rich individuals have a copy of themselves in case they need an organ transplant. Or where scientists grow slaves to work twenty hour days in fast food restaurants.
    All these situations have been in films and they are all examples of the science fiction of human cloning.  Although scientists have not cloned humans, some people believe that this is inevitable …
    Cloning is when scientists make a genetically identical copy of an organism in a nonsexual way. It has been used for many years to produce plants (even growing a plant from a cutting is a type of cloning).
    Scientists have been experimenting with animal cloning for many years. Nobody really talked about it until the birth of the first cloned mammal in 1996, a sheep called Dolly. Since Dolly, many scientists have cloned other animals, such as cows and mice. These recent successes in cloning animals have caused great controversy amongst scientists, politicians and the public.
    So how is cloning done? There are two processes which can be used to clone an organism. The first is artificial embryo twinning. This is the less technologically advanced way to clone. As the name suggests , this technology is similar to when identical twins are created in nature.
    In the natural world, twins happen after the fertilization of an egg cell by a sperm cell. When the fertilized egg tries to divide into a two-celled embryo, the two cells separate. Each cell continues dividing independently, this means there are now two separate babies inside the mother. Because the two cells came from the same egg, the twins are identical at a genetic level.
    Artificial embryo twinning does the same thing, but it takes place in a petri dish instead of in the female’s body. Scientists do this by separating a very early embryo into individual cells. They then allow each cell to divide and develop on its own. These embryos are placed into a surrogate mother, who later gives birth to the babies. The embryos are genetically identical because they came from the same egg.
    Another cloning method is somatic cell nuclear transfer, abbreviated to SCNT. This is different from artificial embryo twinning, however it produces the same result - an exact clone, or genetic copy, of an organism. This was the same method used to create Dolly the Sheep.
    A somatic cell is any cell in the body except the two types of reproductive cells (the sperm and the egg). The somatic cells of all mammals have two complete sets of chromosomes. However, the sperm and egg cells only have one complete set of chromosomes.
    To make Dolly the sheep, researchers took a somatic cell from an adult female sheep. Next, they transferred the nucleus from that cell to an egg cell, which didn’t have a nucleus (it had been removed). After some chemical changes, the egg cell, with its new nucleus, was behaving just like a newly fertilized egg. It developed into an embryo, which was implanted into a surrogate mother.
    The fertilization of an egg by a sperm and SCNT both produce an embryo. So what exactly is the difference between these methods? An embryo is made of cells that contain two complete sets of chromosomes. The difference between fertilization and SCNT is where those two sets came from.
    In fertilization, the sperm and egg both contain one set of chromosomes. When the sperm and egg join, the fertilized egg has two sets of chromosomes - one from the father (sperm) and one from the mother (egg).
    In SCNT, Scientists remove the single set of chromosomes in the egg cell and then replace it with the nucleus from a somatic cell (this already contains two complete sets of chromosomes). Therefore, in this type of embryo, both sets of chromosomes come from the somatic cell – from one organism, not two.
    If scientists clone humans, they will probably use SCNT - the same procedure that was used to make Dolly the sheep. With scientific advances , it seems certain that one day scientists will have the ability to clone humans. The