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Monitoring Stem Cell Research 
When injected into a blastocyst, ES cells form normal 
chimeras. It appears that the presence of surrounding “normal" cells, 
i.e. cells that are derived from a fertilized embryo, prevents an 
abnormal phenotype of the chimera such as the "Large Offspring 
Syndrome" that is typical for cloned animals. Any therapeutic 
application creates, of course, a chimeric tissue vrhere cells derived 
from ntES cells are introduced into a diseased adult individual and 
interact with surrounding "normal" host cells. Therefore, no 
phenotypic abnormalities, such as those seen in cloned animals, 
would be expected in patients transplanted with cells derived from 
ntES cells. 
vm. SCNT for cell therapy: destruction of potential human life? 
A key concern raised against the application of the nuclear 
transplantation technology for tissue therapy in humans is the 
argument that the procedure involves the destruction of potential 
human life. From a biological point of view, life begins with 
fertilization when the two gametes are combined to generate a new 
embryo that has a unique combination of genes and has a high 
potential to develop into a normal baby when implanted into the 
womb. A critical question for the public debate on SCNT is this one: 
is the cloned embryo equivalent to the fertilized embryo? 
In cloning, the genetic contribution is derived from one individual 
and not from two. Obviously, the cloned embryo is the product of 
laboratory-assisted technology, not the product of a natural event. 
From a biological point of view, nuclear cloning does not constitute 
the creation of new life, rather the propagation of existing life 
because no meiosis, genetic exchange and conception are involved. 
Perhaps more important is, however, the overwhelming evidence 
obtained from the cloning of seven different mammalian species. As 
summarized above, the small fraction of cloned animals that survive 
beyond birth, even if they appear “normal" upon superficial 
inspection, are likely not so. The important conclusion is that a 
cloned human embryo would have little if any potential to develop 
into a normal human being. With other words, the cloned human 
embryo lacks essential attributes that characterize the beginning of 
normal human life. 
Taking into account the potency of fertilized and cloned embryos, 
the following scenarios regarding their possible fates can be 
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