Germ Plasm - Germ Plasm Theory

Germ Plasm Theory

The term germ plasm was first used by the German biologist August Weismann (1834–1914). His germ plasm theory states that multicellular organisms consist of germ cells that contain and transmit heritable information, and somatic cells which carry out ordinary bodily functions. In the germ plasm theory, inheritance in a multicellular organism only takes place by means of the germ cells: the gametes, such as egg cells and sperm cells. Other cells of the body do not function as agents of heredity. The effect is one-way: germ cells produce somatic cells, and more germ cells; the germ cells are not affected by anything the somatic cells learn or any ability the body acquires during its life. Genetic information cannot pass from soma to germ plasm and on to the next generation. This is referred to as the Weismann barrier. This idea, if true, rules out the inheritance of acquired characteristics as proposed by Jean-Baptiste Lamarck.

The part of Weismann's theory which proved most vulnerable was his notion that the germ plasm (effectively, genes) were successively reduced during division of somatic cells. As modern genetics developed, it became clear that this idea was quite wrong. Cases such as Dolly (the famous cloned ewe) which, via somatic cell nuclear transfer, proved that adult cells retain a complete set of information – as opposed to Weismann's increasingly determined gradual loss of genetic information – putting this aspect of Weismann's theory to rest.

The idea was to some extent anticipated in an 1865 article by Francis Galton, published in Macmillan's Magazine, which set out a weak version of the concept. In 1889 Weismann wrote to acknowledge that "You have exposed in your paper an idea which is in one essential point nearly allied to the main idea contained in my theory of the continuity of germ-plasm".