Basic explanation
The whole world was surprised when Dolly the sheep was born as she was the first cloned
mammal. In fact, cloning a sheep was not the goal of the team who actually only wanted to
know if the body cell – its nucleus – encloses complete genetic information for the animal as
do the gametes (eggs and sperm). They took the egg of sheep – an oocyte – removed its
nucleus and replaced it by the nucleus of the standard cell of a sheep body. The oocyte with
the inserted nucleus divided thereby making an embryo. Scientists then transferred it into the
uterus of another sheep. The birth of Dolly was a very convincing positive answer to their
question. Since then several other mammals have been successfully cloned. It is therefore
highly possible that human beings could also be cloned provided undamaged DNA is
available - the hair cell might be a source of it. However, such experiments are prohibited in
all countries so experimental verification is not available.
The need for undamaged DNA is the main obstacle in the cloning of extinct organisms.
Discoveries of the remains of extinct organisms seldom provide enough high quality DNA to
allow cloning.