Does cloning create identical copies?

EMBRYOS ARE MADE OF STEM CELLS that divide to give rise to different types of cells, everything from skin to brain cells. Scientists once thought that reproductive cloning creating a genetically identical copy of an individual organism - would be impossible without using stem cells and that the path leading to mature 'differentiated' cells was irreversible. But clawed frogs proved them wrong...

- JV CHAMARY

What makes cloning possible?

In 1958, biologist John Gurdon inserted the nucleus from the mature gut cell of an adult frog into an egg whose nucleus had been removed. This produced tadpoles that were clones of the frog that donated the gut cell.

Gurdon's experiment showed that mature cells can be reprogrammed to become stem cells. We now know that proteins within an egg cell are what control the genetic instructions in DNA that direct a cell to become a specific type. Reversing that programming let researchers sidestep some ethical issues over using embryonic stem cells, while also paving the way for artificial cloning of complex creatures.

Why was Dolly the sheep so special?

Dolly was the first mammal to be produced by transferring the nucleus from a mature cell into an empty egg. Because the nucleus came from a body or 'somatic' cell from the udder of an adult sheep, the clone was named after buxom country singer Dolly Parton. The lamb, carried to term by a surrogate ewe, was born in 1996.