ABSTRACT
Non-identical twins arise when two different sperms fuse with two separate eggs at the same time, resulting in two offspring. These are as dissimilar as any singly conceived individuals and, indeed, are frequently of different sex. Animal clones of all shapes and sizes have existed for millennia. The birth of Dolly, a cloned lamb, heralded a revolution in reproductive technology because she did not have a genetic mother or father but was instead ‘propagated’ by taking a piece of one sheep and treating it in such a way that it grew into a new identical animal. Sex produces diversity; clones produce uniformity. Dolly carried exactly the same genetic information as her predecessor despite the fact that she did not share its parents. Scientists had found a way to avoid the lottery of sexual reproduction by developing procedures allowing them to obtain both recipe books from an adult animal and implant them in a prepared womb.
