Nature was cloning organisms hundreds of millions of years before Dolly
Dolly the sheep made headlines in 1996 as the first mammal cloned from an adult body cell, but cloning itself is ancient. Bacteria splitting in two, plants sprouting from runners and identical twins all produce genetically matching copies. Nature has been making clones for hundreds of millions of years without any laboratory help.
A clone is an organism or cell with a genome identical to its source. The word was coined by Herbert J. Webber in 1903 from the Ancient Greek klon, meaning twig, a nod to growing a new plant from a cutting. Horticulturists spelled it clon until the early twentieth century, when the final e was added to show the o is long. Natural cloning happens through binary fission, budding, fragmentation and parthenogenesis, in which an organism reproduces without a mate. Blueberries, hazel trees and the Pando trees are all known for it.
Dolly came from somatic-cell nuclear transfer. Scientists remove the nucleus from an egg and replace it with the nucleus of an ordinary body cell; the egg then reprograms that nucleus and begins developing into an embryo genetically identical to the donor. The same technique could in principle generate embryonic stem cells matched to a patient, an approach called therapeutic cloning. A cloned human blastocyst has been created, though stem cell lines from such a source have yet to be isolated.
In molecular biology, cloning usually means copying pieces of DNA. The process has four stages: cutting DNA into fragments, joining a chosen fragment into a carrier molecule called a vector, inserting that into cells, and screening for cells that took it up. Because success rates are low, vectors carry markers such as antibiotic resistance so only transformed cells survive, and some add a colour test that shows blue or white colonies. Cloning single cells from bacteria or yeast is simple, whereas cells from complex organisms are far harder to grow.
Cloning stirs strong ethical debate, especially around embryonic stem cells. It has also been floated as a way to revive extinct species, and science fiction regularly explores cloned humans, recreated historical figures and questions of identity.
Source: Cloning
