Clone and Cloning

Recent years revealed that some cloned animals suffer from age-related diseases and die prematurely.

Although, clones from other species still appear healthy, mice cloned using somatic cells have a higher than expected death rate from infections and hepatic failure.

Plagued with a chronic and progressive lung disease, veterinarians were forced to humanly euthanize Dolly in February 2003. Dolly lived approximately 60% of the normal lifespan of sheep (normally 11 to 12 years) and developed other conditions (e.g., chronic arthritis) much earlier than expected in a sheep's normal lifespan. Dolly's seemingly fragile health, along with more generalized fears of premature aging in cloned animals, renewed fears first raised by a study in 1999 that Dolly's telomeres were shorter than normal.

Telomeres are the physical ends eukaryotic chromosomes and play a role in the replication and stabilization of the chromosomes upon which they reside. Telomeres are synthesized by the enzyme telomerase. Telomerase is one of the factors believed to control the length of telomeres that may act as a biological clock for the cell.

According to the telomere theory of aging, during DNA synthesis, DNA polymerase fails to replicate all of the nucleic acids resulting in shortened telomeres—and hence shortened chromosomes—with each successive generation of cell division. Eventually, the cell will no longer divide and after enough critical regions have been deleted, the cell cycle will arrest and the cell will die.

Because telomerase is not active all the time, nor is it found in every cell of the body, the genetic regulation of telomerase is under intense study. Researchers have discovered that if the action of telomerase is interrupted, the telomere will abnormally shorten and thus accelerate the general aging process of the cell.

At a minimum, cloning eliminates genetic variation and thus, can be detrimental in the long term, leading to inbreeding and increased susceptibility to diseases. Although cloning also holds promise for saving certain rare breeds of animals from extinction, for some of them, finding the surrogate mothers can be a challenge best illustrated by failed trials with cloning of pandas.