In 1997, Dolly rocked the world of genetics. Not baaaa'd for a little lamb from Scotland. What was the big deal? She was the first mammal to be cloned with DNA from an adult cell. Before Dolly, clones had been created using DNA from very young cells. Dolly is her mother's identical twin, only six years younger.

Image credits: main image, Kelvin Chan/© AMNH.