As Carey surveys the field, she dwells on early development as a critical period when environmental influences can affect epigenetic controls with long-term effects. None of these controls is evident when sperm meets egg and undergoes initial cell divisions, which explains why “embryonic stem cells” are prized for their ability to develop into any cell type. Epigenetics is the study of those DNA controls, the key players for which are proteins that attach methyl groups to selected parts of DNA and proteins that add acetyl groups to histones (proteins associated with DNA on chromosomes). Some of this DNA is transcribed as “non-coding RNA” with various functions, and some codes for proteins that determine which genes are expressed and which genes are silent in a given cell type-a liver or a skin cell, for example-ensuring that when these cells divide, the daughter cells will be the same type.
British virologist Carey tackles epigenetics with a passion to explain a rapidly developing and complex field.Įarly on the author reminds us that a surprising finding from human-genome research is that only two percent of the DNA in our cells codes for proteins used in the body. Though it was once fashionable to call the rest “junk” DNA, that’s not the case today.
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