Fateful imprints

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Science  13 Jan 2017:
Vol. 355, Issue 6321, pp. 122-125
DOI: 10.1126/science.355.6321.122

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Imprinting means that in some places along the human genome—about 100 genes in all—the way DNA behaves depends on which parent passes it to the offspring. Some of the genes in sperm and egg cells have chemicals called methyl molecules that attach to them, a process called methylation; these molecules can either activate or silence a gene. In some cases, the mother's copy of the gene is activated, and the father's silenced. In others the opposite is true. The function of each of the dozens of human imprinted genes isn't yet known, but many appear to guide metabolism and growth prior to birth. When imprinting goes awry—and researchers don't understand yet why that happens—the outcome can be health problems in the baby. The last several years have seen imprinting disorders emerge from the shadows, and with them a deeper appreciation for the human genome's ability to modulate gene expression in the earliest stages of development. Scientists are also considering how imprinting errors could cause cancer or stunt fetal growth.