表观遗传学教程1节.ppt

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* * * * The Most Difficult Definitions in Science: Nature (2008) 455: 1023-1028 Paradigm shift Epigenetic Complexity Race Tipping point Stem cell Significant Consciousness No one denies that epigenetics is fashionable: its usuage in PubMed papers increased by more than tenfold between 1997 and 2007. And few deny that epigenetics is important. What they do disagree on is what it is. “Epigenetics is a useful word if you don’t know what’s going on – if you do, you use something else” -- Adrian Bird The definition of “Epigenetics” The term epigenetics was introduced by Conrad H. Waddington (1905-1975) in 1942 to describe “the interactions of genes with their environment that bring the phenotype into being”. The current term of epigenetics: changes in phenotype that are inheritable but do not involve DNA mutation. Waddington’s classical epigenetic landscape: in 1957, Waddington proposed the concept of an epigenetic landscape to represent the process of cellular decision-making during development. At various points in this dynamic visual metaphor, the cell (the ball) can take specific permitted trajectories, leading to different outcomes of cell fates. Over the years, numerous biological phenomena, some considered bizarre and inexplicable, have been lumped into the category of epigenetics. Genetics Epigenetics mutations alterations Position-Effect Variegation (PEV) (H.J. Muller, 1930) In Drosophila, virtually every gene that has been examined in an appropriate rearrangement has been shown to variegate, and rearrangements involving the pericentromeric heterochromatin of any chromosome can lead to PEV. PEV has also been observed in a variety of organisms. Genetically defined Su(var) and E(var) genes and their functions (from ~30) Paramutation (R.A. Brink, 1958) Brink described his stunning observations of “paramutation” at the R locus in maize in 1958. Several similar loci were later again discovered in maize. ~9000

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