Dolly was born on July 5, 1996. The udder cells used to clone Dolly came from a six-year old sheep. There are two different reasons why Dolly might be older than she looks. Telomere Shortening Telomeres are caps of DNA at the ends of chromosomes, and some scientists believe they tick like a biological clock to control how long an organism lives. As each cell replicates, the telomeres grow progressively shorter.
Scientists believe cells stop replicating when the telomeres reach some critical length.
Research is in progress to determine if this phenomenon is seen in other organisms and whether or not it is important. Damage to DNA Over an organism's lifetime, the DNA within its cells deteriorates, and unrepaired damage causes some diseases, including cancer. Scientists are concerned that this accumulated damage may be carried along during the cloning process. There are a variety of views on the ethics of cloning. Even if perfectly healthy clones can be generated, some people believe that it shouldn't be done.