In the video below, you can watch a mouse embryo develop over the span of five days. According to Erica Watson, a Next Generation Research Fellow at the Centre for Trophoblast Research at the University of Cambridge, the first embryo in the video is nine days old and roughly the thickness of a penny. The last embryo is nine days old and approximately the size of a blueberry.

According to Watson, mice are ideal for this kind of research because they use the same genes during development as humans. "Compared to a human pregnancy that lasts nine months," Watson says, "a mouse fetus develops quickly, taking only three weeks to get from a one-cell embryo to a fully-grown mouse pup."

SOURCE: University of Cambridge