National Geographic : 2012 Jan
Reading disability Autism Major affective disorder Alcoholism Alzheimer's Schizophrenia Hypertension Diabetes Multiple sclerosis Breast cancer Crohn's disease Stroke Rheumatoid arthritis Identical Fraternal 0% 50 100 Gene expression over time Twin 1 Twin 2 Identical DNA is not altered by tags. Varying tags make twins different. quick to point out, that parents have no impact at all on their children. Without a loving and supportive environment, no child can reach his or her full potential, they said. But when it came to explaining why a particular group of children ended up with di erent IQ scores, 75 percent of the variation was due to genetics, not parenting. Besides the Minnesota project, which ended in 2000, other studies have used twins research to examine all kinds of behaviors and attitudes. One investigation, for example, found that an identical twin with a criminal co-twin was more than 1.5 times as likely to break the law as a fraternal twin in the same situation, suggesting that genetic factors somehow set the stage for criminal behavior. Another study found that the strength of an individual's religious fervor was signi cantly shaped by heredity, though one's choice of a liation---whether to become, say, a Methodist or a Roman Catholic---was not. Wherever scientists looked, it seemed, they found the invisible hand of genetic in uence helping to shape our lives. SAME GENES, DIFFERENT PEOPLE Identical twins are born with the same DNA but can become surprisingly different as they grow older. A booming field called epigenetics is revealing how factors like stress and nutrition can cause this divergence by changing how individual genes behave. SHARED TRAITS Identical twins share certain disorders, such as autism, much more often than fraternal twins do, suggesting the strong influence of heredity. AMANDA HOBBS AND LAWSON PARKER, NGM STAFF SOURCE: ARTURAS PETRONIS, CENTRE FOR ADDICTION AND MENTAL HEALTH, TORONTO Epigenetic tag Tags are chemical mechanisms that can express (activate or suppress) genes to different degrees. They do not change DNA. Scientists suspect some tags can be inherited. What causes tagging? ENVIRONMENTAL influences such as nutrition may change the expression of a gene. RANDOM epigenetic shifts can happen without any outside influences.