that this idea is wrong in most cases. Cases such as Dolly, the cloned sheep, proved via somatic cell nuclear transfer 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 as a general rule of metazoan development. However, genetic information is readily lost by somatic cells in some groups of animals through somatic genome processing. The best known example are the nematodes, in which the phenomenon of chromatin diminution was first described by Theodor Boveri in 1887. 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". Modern view The idea of the Weismann barrier, namely that changes acquired during an organism's life cannot affect its offspring, is still broadly accepted. This has been extended into molecular terms as the central dogma of molecular biology, which asserts that information written in the form of proteins cannot be fed back into genetically transmissible information encoded in nucleic acids. The Weismannian notion that the germ cells are unaffected by somatic cells or their environment is however proving not to be absolute. Chemical modification of the nucleotide bases that constitute the genetic code such as methylation of cytosines as well as modifications of the histones around which DNA is organized into higher-order structures are influenced by the metabolic and physiologic state of the organism and in some cases can be heritable. Such changes are called epigenetic because they do not alter the nucleotide sequence. References External links Germ cells Cytogenetics History of biology