You may have learned about the sheep clone, Dolly, in your science class. Although this experiment was greeted as a great success, there are many problems with cloning. One of the ethical issues surrounding cloning has to do with the success rate of the process. This is because

A) cloning has never been and never will be possible.

B) cloning has become too successful in recent years.

C) cloning mammals has a very low success rate, and can produce severely damaged young.

D) cloning mammals has a very high success rate, and can produce severely damaged young.

C) cloning mammals has a very low success rate, and can produce severely damaged young.

Explanation:

Cloning of mammals has a very low success rate and can produce severely damaged pups. Proof of this was what happened to the Dolly sheep.

The cloning that gave rise to Dolly is also called "nucleus transfer", that is, the nucleus of a somatic cell is removed and placed in an egg whose nucleus was previously removed. This cell is capable of dividing and, if the resulting embryo is implanted in a uterus and succeeds in developing, it can generate an individual. Interesting, or scary, was knowing that 276 attempts were made until Dolly was born, and most of the eggs used, with the nucleus changed, did not even divide. And that of all the other embryos that managed to divide and be implanted, only Dolly was born. All others died during pregnancy, many of them with genetic alterations or severe malformations.

On February 14, 2003, at the age of six and a half, Dolly underwent a lethal injection, as she was the victim of a serious lung disease, of supposedly infectious origin. The scientific community still expects further explanations about the disease that affected the most famous sheep in the world. Could this disease be caused by a genetic error resulting from cloning? Dolly's "breeders", Scottish researchers at the Roslin Institute, said the disease is common in sheep and was probably acquired. But how could Dolly have been exposed to a very serious and fatal disease? It seems strange. In addition, Dolly had previously presented other problems possibly related to cloning. She was big, obese and lived in confinement. She had three pregnancies and six puppies. At just over five and a half years old, information was released that Dolly suffered from arthritis in her left hind leg.

Both arthritis and lung disease presented by Dolly are diseases characteristic of elderly sheep. Arthritis, in particular, was attributed to the fact that Dolly stood on her hind legs for a long time to "play" with visitors. But many vets dispute that justification. The hypothesis that has been discussed is that these diseases, common in older animals, could be associated with the shortening of telomeres (DNA sequences that are at the tip of chromosomes). It is already well known that chromosomes decrease in size and lose small portions of their genetic material over time. When Dolly was three years old, her telomeres were characteristic of a nine-year-old animal, the age that the nucleus donor would have if it were alive. However, this information is not confirmed by its creators, who dispute the results of these tests because they were done only once, in blood tissue. In addition, other cloned animals did not show shortening of telomeres.

C. Cloning mammals has a very low success rate and can produce damaged young