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AP via YahooRemember biology class where you learned that children inherit one copy of a gene from mom and a second from dad? There's a twist: Some of those genes arrive switched off, so there is no backup if the other copy goes bad, making you more vulnerable to disorders from obesity to cancer...Duke University scientists now have identified these "silenced genes," creating the first map of this unique group of about 200 genes believed to play a profound role in people's health.
More intriguing, the work marks an important step in studying how our environment — food, stress, pollution — interacts with genes to help determine why some people get sick and others do not...
Usually, people inherit a copy of each gene from each parent and both copies are active, programmed to do their jobs whenever needed. If one copy of a gene becomes mutated and quits working properly, often the other copy can compensate...Genetic imprinting knocks out that backup. It means that for some genes, people inherit an active copy only from the mother or only from the father. Molecular signals tell, or "imprint," the copy from the other parent to be silent...Jirtle compared it to flying a two-engine airplane with one engine cut off. If the other engine quits, the plane crashes. In genetic terms, if one tumor-suppressing gene is silenced and the active one breaks down, a person is more susceptible to cancer.
Only animals that have live births have imprinted genes. It was not until 1991 that it was proved that humans had them. Until now, only about 40 human imprinted genes had been identified...Previous work by Jirtle and others shows the environment can reprogram how some genes operate, making them speed up or slow down or work at the wrong time. In a groundbreaking 2003 experiment, Jirtle fed pregnant mice different nutrients to alter the coat color of their babies. The feed affected chemical signals that control how hard a certain gene worked, determining when the babies had yellow coats like mom or brown ones.
"It's not just about the sequence of your genes, but how that sequence is turned on and off by environmental exposures that is likely to determine whether you will be healthy," Volkow said. Imprinted genes "are likely to be particularly susceptible to environmental factors." Sometimes imprinting goes awry before birth, leaving a normally silenced gene "on" or silencing one that should not be. Faulty gene imprinting leads to some devastating developmental disorders, such as Angelman syndrome, which causes mental retardation. Now a question is how imprinting may be changed to reactivate an imprinted gene after birth.
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http://news.yahoo.com/s/ap/20071130/ap_on_sc/silenced_genes_2
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