The Machine Theory
Weismann believed that the initial division of the egg into two cells causes determinants to be divided into two groups, such that one cell will develop, say, the left half of the embryo, while the other cell will generate the right half. With each subsequent division, determinants continue to be meted out differently to different cells until the stage is reached where each cell type is in place. At this point the distinct set of determinants in each cell type produce the developmental machinery that will generate the tissue, organ or system associated with that type of cell.
Weismann’s developmental concept was based on a mistaken interpretation of an 1882 experiment carried about by Wilhelm Roux, in which Roux killed one of the cells of a frog embryo at the two-cell stage. The remaining cell then led to half an embryo, leading Weismann to believe that the determinants for the embryo were divided along with each cell division. As Hans Driesch and other researchers discovered, when the dead cell is removed, the other cell produces a whole organism, not half. It's now well known that all the cells in a given organism contain the same set of genes.
Read more about this topic: Genetic Determinism
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