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POSTED 23 JULY 1998.
More than one year after screaming headlines about Dolly, the cloned sheep, scientists have finally verified her peculiar ancestry. In letters published in Nature (23 July 1998), two groups of scientists reported separate DNA fingerprinting analyses. Their conclusion? Dolly, is indeed a clone -- an exact genetic replica -- of the nameless ewe that "donated" genetic material to the experiment.
Dolly, you'll recall, resulted from the fusion of a sheep egg cell -- whose genetic material had been removed -- with the nucleus (which carries chromosomes) from an adult cell taken from another sheep. (Removing the genes from the egg cell prevents it from growing normally and makes room for the new genes. It also helps ensure that the clone is really a clone.)
Although cloning sounds like science fiction to most of us, to scientists the real breakthrough is in forcing the genes of an adult cell to mimic the genes of a freshly fertilized egg. Normally, a skin cell (to take one example) can only make more skin cells. In contrast, egg cells can form every cell type in an adult animal.
Since Dolly's arrival, some scientific critics had speculated that the comely ewe might have resulted from a laboratory accident, but the publication of two genetic proofs should settle that argument.
Nice mice cloning
The researchers used a variety of slightly different techniques than those used to make Dolly, and obtained a somewhat higher success rate. While Dolly's creators had used adult mammary gland cells, Wakayama's group used cells that surround the mouse egg cells. To prove that the clones were legitimate, they cloned black mice into egg cells taken from white mice.
Finally, they raised the mouse clones to adults and bred them to demonstrate that they made normal offspring. And in a stroke of genius, they then successfully cloned the clones!
The Why Files can't begin to describe the family tree of those clones...
As if confirming Dolly's bizarre heritage wasn't enough, scientists have also repeated the cloning process -- and taken it several steps further. In the same issue of Nature, a team headed by Ryuzo Yanagimachi of the University of Hawaii said they'd created 22 mice based on the genetics of adult animals.
-- David Tenenbaum
