一、 WASHINGTON (AP) — Remember biology class where you learned that childreninherit one copy of a gene from mom and a second from dad? There's a twist: Some ofthose genes arrive switched off, so there is no backup if the other copy goes bad, makingyou more vulnerable to disorders from obesity to cancer.                Duke University scientists now have identified these "silenced genes," creating thefirst map of this unique group of about 200 genes believed to play a profound role inpeople'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 getsick and others do not.