Stresses placed on both the egg cell and the introduced nucleus during somatic cell nuclear transfer are enormous, leading to a high loss in resulting cells. For example, Dolly the sheep was born after 277 eggs were used for SCNT, which created 29 viable embryos. Only three of these embryos survived until birth, and only one survived to adulthood. Here is a comprehensive report on the limitations and ethical considerations of cloning.
In 1997, Scottish scientists revealed they had cloned a sheep and named her Dolly, sending waves of future shock around the world that continue to shape frontiers of science today. (Here's the article.)
It’s the dream of kids all around the world to see giant beasts walk the Earth again. Could — and should — that dream be realized? Hendrik Poinar gives an informative talk on the next — really — big thing: The quest to engineer a creature that looks very much like our furry friend, the woolly mammoth. The first step, to sequence the woolly genome, is nearly complete. And it’s huge.
The purpose of Sheep 101 is to teach people about sheep, their products, how they are raised, and their contributions to society.
The gastric brooding frog lays its eggs just like any other frog — then swallows them whole to incubate. That is, it did until it went extinct 30 years ago. Paleontologist Michael Archer makes a case to bring back the gastric brooding frog and the thylacine, commonly known as the Tasmanian tiger.
Watch Billy Nye's episode about cloning.

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