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Weismann, August

germ cells plasm chromosomes

[ viys man] (1834–1914) German biologist: devised a theory of heredity.

Weismann qualified in medicine and practised for a few years before the attractions of biological research drew him to university teaching in Freiburg, a town which he greatly liked. He was a skilled microscopist, but failing sight from 1864 eventually pushed him to become a theorist, with a special interest in heredity. Basing his ideas in part on his earlier work on the sex cells of hydrozoa, he proposed that all organisms contain a ‘germ-plasm’, associated especially with the ovum and sperm cells, which he later located in what are now called the chromosomes. In his view, it was germ-plasm that gave the continuity from parent to off-spring. All other cells are merely a vehicle to convey the germ-plasm, and it alone is in a sense immortal; other cells are destined to die. As Samuel Butler the satirist phrased it, ‘a hen is only an egg’s way of producing another egg’. Weissman saw the major events in reproduction as the halving of the chromosome number in germ-cell (ova and sperm) formation, and in the later union of chromosomes from two individuals; he suggested that variability resulted from the combination of different chromosomes. His ideas are of course broadly correct, and it is surprising that he was able in the 1880s to get so near the modern view. He was wrong in his belief that the germ plasm is unalterable and immune to environmental effects, as others were later to demonstrate.

Early in his work Weissman believed (rather ineptly) he had demonstrated that acquired characters are not inherited: he cut off the tails of a family of mice for 22 generations, mutilating 1592 mice, but they still failed to produce tail-less offspring.

Weizmann, Chaim [next] [back] Weinberger, Caspar

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