Genes as mirrors of life experience

　　For decades, researchers have ransacked the genetic pedigrees of people with mental illness, looking for common variations that combine to cause devastating conditions like schizophrenia and bipolar disorder. The search has stalled badly; while these disorders may involve genetic disruptions, no underlying patterns have surfaced—no single gene or genes that account for more than a tiny fraction of cases.

　　So scientists are turning their focus to an emerging field: epigenetics, the study of how people’s experience and environment affect the function of their genes.

　　Genes are far more than protein machines, pumping out their product like a popcorn maker. Many carry what are, in effect, chemical attachments: compounds acting on the DNA molecule that regulate when, where or how much protein is made, without altering the recipe itself. Studies suggest that such addon, or epigenetic, markers develop as an animal adapts to its environment, whether in the womb or out in the world—and the markers can profoundly affect behavior.

　　In studies of rats, researchers have shown that affectionate mothering alters the expression of genes, allowing them to dampen their physiological response to stress. These biological buffers are then passed on to the next generation: rodents and nonhuman primates biologically primed to handle stress tend to be more nurturing to their own offspring, and the system is thought to work similarly in humans.

　　Epigenetic markers may likewise hinder normal development: the offspring of parents who experience famine are at heightened risk for developing schizophrenia, some research suggests—perhaps because of the chemical signatures on the genes that parents pass on. Another recent study found evidence that, in some people with autism, epigenetic markers had silenced the gene which makes the receptor for the hormone oxytocin. Oxytocin oils the brain’s social circuits, and is critical in cementing relationships; a brain short on receptors for it would most likely struggle in social situations.

　　At least one group of researchers argues that chemical markers help resolve a biological competition between maternal and paternal genes in the developing fetus. In the traditional view of reproduction, genes from the mother and father work together as collaborators, sharing the duties of creating a new life. But a novel theory holds that the genes are in fact in competition, at various points along the newly forming fetus’s genome. If the system goes awry and brain development tilts too strongly toward the father, a result can be autism, these scientists suggest; too heavily toward the mother, and the child may develop mood disorders.

　　By studying genes at the “epi” level, scientists are hoping to discover patterns that have been elusive at the level of the genes—and ideally to find targets for calibrated treatments that would not simply shut off errant genes but would gradually turn their activity up or down, like adjusting the balance on a stereo.

　　1. The word “surface” (Para 1, Line 4) most probably means ________________.

　　A. arise B. discover C. create D. underline

　　2. Genes ________________.

　　A. produce protein in a sophisticated way

　　B. act on the DNA molecule to alter the recipe

　　C. control the place and amount of protein production

　　D. profoundly affect the behaviour pattern of a human

　　3. According to the passage, what will affect people’s ability to deal with stress?

　　A. Mother’s love. B. Psychological state

　　C. The expressions of genes. D. Nutrition.

　　4. Oxytocin can help people ________________.

　　A. oil the brain

　　B. consolidate relationships

　　C. have smooth blood circulation

　　D. fight against disadvantageous social situations

　　5. According to a recent research, genes from the mother and father ________________.

　　A. in collaboration B. in cooperation

　　C. in competition D. in harmony