Next, they took an unfertilized egg from a second sheep and removed its DNA, carefully sucking it out with a thin glass tube called a pipette. Then they placed the udder cell into the egg and fused the two with a small electric current. This same electric current triggered the egg to begin development into an embryo. The embryo was implanted into a third sheep, and 148 days later, Dolly was born, a healthy clone of the "donor" ewe.
  The procedure described above--the cloning of an adult mammal--was thought to be impossible, because it was thought that parts of the DNA in the specialized cells of an adult mammal were irreversibly "shut down," leaving a genetic blueprint that was complete but only partially readable. The successful cloning of an adult sheep showed that DNA from the cells of an adult can be "reactivated" and used to generate a genetically identical clone.  

Shortly after the Dolly announcement was made, scientists in Oregon announced that they had used a related technique to clone monkey embryos. In this simpler two-step process, a monkey embryo was first created with the standard technique of stirring monkey eggs and sperm together. Once the embryo divided into eight cells, the cells were carefully separated, and DNA from each cell was inserted into fresh egg cells whose DNA had been removed. These cells then grew into embryos that were implanted into female monkeys.

Unlike the process that created Dolly, the Oregon technique is not technically considered cloning, since the cells used were from embryos and not from an adult. However, this research does bring the cloning question a little closer to home, adding to a growing body of evidence that suggests that human cloning is possible--maybe even close at hand.

The Cloning Question...


Bottom Bar

©1997 Exploratorium