CLONING DOLLY- AN EXAMPLE

The cloning of Dolly has proved that cloning of adult animals could be accomplished. Previously, it was not known if an adult nucleus was still able to produce a completely new animal. Genetic damage or the simple deactivation of genes in cells were both considered possibly irreversible. This however was not the case. Ian Wilmut and Keith Cambell discovered a method with which to synchronize the cell cycles of the donor cell nucleus and the host egg cell cytoplasm. Without synchronized cell cycles, the donor nucleus would not be in the correct state for the host egg to accept it. The donor cell was forced into the Go stage of the mitotic cell cycle by starving the cells. When the nucleus enters the egg cytoplasm, egg proteins "re-program" the chromosomes in the nucleus. The dividing embryo is transferred into the oviduct of a surrogate mother sheep. The embryo continues to divide and then implants in the uterine wall.

Steps:

1. The nucleus of an egg is removed.
2. The donor cell is starved. The absence of nutrients causes the cell to enter a suspended state, matching the state of the enucleated egg cell.
3. The donor cell is placed near the egg cell, and a electric current is used to fuse the cells together and stimulate the development.The donor cell's nucleus directs the development of the egg cell.
4. The developing egg is placed in a sheep's oviduct for six days.The oviduct acts as an incubator and embryo develops.
5. Embryo is transplanted to the uterus of the surrogate mother ewe. it carries the embryo till birth.
6. After a normal pregnancy, the clone is born. It is the exact genetic duplicate of the adult.

References:

http://www.luc.edu/faculty/wwasser/dev/shclone.htm