Conceiving a Clone : 1885

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1885: Weismann's Hypothesis.

In 1885, August Weismann, a well respected professor of zoology and comparative anatomy at the University of Freiberg put forth a theory stating that the genetic information of a cell diminishes as the cell differentiates. According to Weismann, each daughter cell had half the genetic information of its parent cell. Weismann’s theory was an answer to the puzzling question of why a cell develops to become specialized in function despite the fact that all cells in an organism originate from the same fertilized egg.

Following the announcement of Weismann’s theory, embryologist William Roux published the results of an experiment that he claimed affirmed Weismann’s belief. Roux used a hot needle to destroy one cell of a two celled common frog embryo (The two celled embryo is called a blastomere. The frog’s scientific name is Rana esculenta). According to Weismann’s theory, since the frog’s embryo had already divided into a two celled blastomere, each cell would only have half of the genetic information needed to create an entire frog. As a result, Weismann’s theory predicted the individual cells could only grow into half an embryo. In Roux’s experiment, this is exactly what happened.

Following Roux’s work, Hans Adolf Edward Dreisch tried to repeat this experiment with sea urchins. Instead of destroying one of the cells of the two celled embryos with a hot needle as did Roux, Dreisch shook the two cells of the sea urchin embryos apart. In Dreisch’s experiment, each individual cell grew into a complete live sea urchin. This result flatly contradicted Weismann’s theory, which stated that each cell should develop into half an embryo and then half a creature. Dreisch repeated his experiment, and was able to break apart four-celled sea urchin embryos and grow complete sea urchins from each individual cell. He stated that Roux’s individual cells did not grow to be complete frogs because the hot needle Roux used not only destroyed one cell, but damaged the other cell of the blastomere.

The questions raised by Roux and Dreisch’s experiments led to Hans Spemann’s work on the subject in 1902.

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