研究生英语课件以及课后详细答案第六单元.pptVIP

Unit Six Is It in the Genes? By Arthur Allen Questions Text In 1993, a National Cancer Institute researcher named Dean Hamer made what seemed to be an astonishing discovery about the genetics of human behavior. He had located a link to male homosexuality on the X chromosome, Hamer reported in Science. The story was splashed across front pages around the country. At last, overly doting mothers and early cross-dressing games were off the hook and the predilections of everyone from Walt Whitman to Liberace could be explained by a few errant proteins. Hamer’s article, based on an examination of the DNA of 40 gay brothers, led to mass-market book deals and minor celebrity. There is only one small, under reported glitch: Hamer’s results have never been replicated. Two subsequent studies showed much weaker evidence of a gay gene; a third, published on April 23 but overshadowed by the massacre at Littleton the day before, found no evidence at all. “There is no hint or trend in the direction of the initial observation,” George Ebers, a Canadian investigator involved in the study, said in Science. A quick trawl through the headlines of the 1990s finds a similar fate for other frontgenetic breakthroughs. Despite much-publicized discoveries of genes for schizophrenia, manic-depression, alcoholism and bipolar disorder, the precise genetic component of these illnesses continue to elude science. The same goes for personality traits. The much-trumpeted discovery of a “novelty-seeking gene” in 1996 hasn’t been replicated—nor have various “depression genes”. This is not to say that progress isn’t being made in parsing the biological components of behavior. But in any given person, the interplay of genes and the environment is a horrendously complex story. Individual genes produce quite subtle effects, and the more we learn about DNA, the clearer it is that any particular gene’s potential can be shut down or enhanced by complex biochemical pathways conti