Editing Germ plasm (section)

==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 [[protein]]s cannot be fed back into genetically transmissible information encoded in [[nucleic acid]]s.<ref>{{cite book |author=Turner, J. Scott |editor1=Henning, Brian G.|editor2=Scarfe, Adam Christian |title=Biology's Second Law: Homeostasis, Purpose, and Desire |work=Beyond Mechanism: Putting Life Back Into Biology |url=https://books.google.com/books?id=naQm1_Lutq4C&pg=PA192 |year=2013 |publisher=Rowman and Littlefield |isbn=978-0-7391-7436-4 |page=192 |quote=Where Weismann would say that it is impossible for changes acquired during an organism's lifetime to feed back onto transmissible traits in the germ line, the CDMB now added that it was impossible for information encoded in proteins to feed back and affect genetic information in any form whatsoever, which was essentially a molecular recasting of the Weismann barrier.}}</ref>

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 [[cytosine]]s as well as modifications of the [[histone]]s 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 [[epigenetics|epigenetic]] because they do not alter the nucleotide sequence.<ref>{{cite journal |author1=Berger, S. L. |author2=Kouzarides, T. |author3=Shiekhattar, R. |author4=Shilatifard, A.  | title=An operational definition of epigenetics |journal=[[Genes & Development]] | volume=23 | issue=7 | pages=781–83 | year=2009 | pmid=19339683 | pmc=3959995 | doi=10.1101/gad.1787609 }}</ref>