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. Weismanns 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 Weismanns theory, embryologist William Roux published the results of an experiment that he claimed affirmed Weismanns 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 frogs scientific name is Rana esculenta). According to Weismanns theory, since the frogs 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, Weismanns theory predicted the individual cells could only grow into half an embryo. In Rouxs experiment, this is exactly what happened.
Following Rouxs 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 Dreischs experiment, each individual cell grew into a complete live sea urchin. This result flatly contradicted Weismanns 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 Rouxs 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 Dreischs experiments led to Hans Spemanns work on the subject in 1902.
Copyright 1998 by team 24355 and Kayotic Development.