Movie: Primary Induction, The Double-Gradient Hypothesis,

About the Movie

This is a ten-minute movie on the story of primary induction and the experiments that led Dr. Lauri Saxén to suggest his double-gradient hypothesis. The movie explains how it was the experiments of Hans Spemann and Hilde Mangold in 1924 that showed that a region of the early amphibian embryo, called the dorsal lip of the blastopore, when transplanted to the ventral side of a host embryo, could induce the host tissues to form a second embryo around the transplant. Lauri Saxén, working with his advisor, Sulo Toivonen, proposed a double gradient hypothesis to explain this phenomenon, suggesting that there were two inducers, and that each inducer was setting up a gradient of inducing agent, and that the interactions between the two gradients allowed for the full induction of structures. Dr. Saxén went on to test this double-gradient hypothesis in a series of ingenious experiments that culminated in a paper in Science showing that the double-gradient model worked on the cellular level.

Sample Slides from the Movie