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Devlin Crose's Blog

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Information transfer

Nearly every multicellular organism passes through a life cycle stage where it exists as a single undifferentiated cell or as a small number of undifferentiated cells. This developmental stage contains molecular information which specifies the entire course of development encoded in its many thousands of genes. At the molecular level, genes are used to make proteins, many of which act as enzymes, biological catalysts which drive the thousands of different biochemical reactions inside cells. 

Development (Zarucha, T. 2004)

Epigenesis The view of development where structures arise progressively (p. 95).

Kaspar Friedrich Wolff (1733–1794) observed that during chick development, embryonic structures, such as the heart and kidneys, look very different from the adult structures into which they develop. If preformation were the mechanism by which development was proceeding, embryonic and adult structures would appear identical, only differing in their size. Wolff also observed that structures such as the heart actually developed anew in each embryo. The view of development that Wolff observed, where structures arise progressively, is known as epigenesis (a Greek word meaning “upon formation”). Interestingly, the idea of epigenesis as the over-riding mechanism of development was first recognized and supported by the Greek philosopher Aristotle (384–322 B.C.).


Epigenetic Inheritance (Smelser, N. J. & Baltes, P. B., 2001, pp – 4800 – 4804) ‘Epigenetic inheritance’ is a term used to describe the transmission from one generation to the next of structural and functional variations that do not depend on genetic differences. In its broadest sense, the term includes the transmission of nongenetic variations in behavior, but its use is usually restricted to the inheritance in cell lineages of variations that are not based on changes in the genetic information carried in DNA. Such heritable epigenetic changes are part of normal development but there is increasing evidence that they can also be transmitted from one generation of organisms to the next. Epigenetic inheritance therefore has practical implications for medicine and agriculture, and theoretical implications for ideas about heredity and evolution. The introduction of the term ‘epigenetics’ by the British embryologist Conrad Waddington in 1947 (see Waddington 1975), reflected a growing interest in the relationship between genes and development, an interest which increased as the molecular nature of the gene was unraveled. Waddington coined the term epigenetics for the study of the causal mechanisms of development; the adjective ‘epigenetic’ is applied to the processes through which the genetic information in a fertilized egg is expressed and used in the production of the adult form, the visible phenotype. The concept of epigenetic inheritance was therefore extended and now has both a narrow and a broad meaning. The narrow meaning limits it to cell memory in lineages within an organism, whereas the broad meaning includes the transmission of epigenetic information between any reproducing entities—cells, individuals, and even groups of individuals. This article focuses first on epigenetic inheritance in cell lines, and then discusses the consequences of the transmission of epigenetic variations between generations of individuals.

Mechanisms of Transmission

The systems that underlie epigenetic inheritance and enable the phenotypic expression of the genetic information in a cell to be transmitted to the next generation have been called epigenetic inheritance systems (EISs). Three broad types have been characterized (Jablonka and Lamb 1995): steady-state systems, structural systems, and chromatin-marking systems.


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