Willadsen clones a mammal.
Danish scientist Steen
succeeded in cloning a sheep from embryo cells. Willadsen's work was the
first verified cloning of a mammal using the method of nuclear
In 1979 Karl Illmensee claimed to have
through nuclear transfer, but his results were
strongly brought into question by the scientific
community. In earlier experiments, Willadsen had cloned
mice by dividing single celled embryos in two with a
method similar to that of Hans
Spemann's tadpole studies in 1902.
Willadsen fused a cell from an eight-cell lamb embryo with an unfertilized egg whose nucleus had been removed. Traditionally, scientists had used fertilized eggs in the nuclear transfer process. Willadsen found that unfertilized eggs more easily received the transplanted nucleus. The egg was then tricked into thinking it had been fertilized.
Then the fertilized embryos were coated in agar and placed into the oviducts of sheep where they grew for a short period of time. After about a week of growing in the oviducts, Willadsen extracted the embryos of placed each into a uterus of a surrogate mother. From the experiment, two lambs died at birth, and another survived to be the first cloned mammal by the nuclear transfer method. Willadsen's feat had only months ago been referred to as biologically possible.