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性取向的生物学机制不但是人类遗传学中最令人头疼的问题之一,而且在政治上高度敏感。如今研究人员发现同性恋与受环境影响的DNA标记存在某种联系。双胞胎研究与家谱信息为“性取向至少在一定程度上是由遗传因素决定的”这一观点提供了强有力的证据。当同卵双胞胎中的一个是同性恋时,另一个也是同性恋的概率只有20%,因此研究人员认为环境因素也起了一定作用,其中己被研究的环境因素之一是“兄长效应”:每多一位兄长,男性成为同性恋的概率
The biological mechanism of sexual orientation is not only one of the most troubling problems in human genetics, but it is also politically highly sensitive. Now researchers have found that homosexuality has some connection with DNA markers affected by the environment. Twin studies and pedigree information provide strong evidence that “sexual orientation is at least partly genetic”. When one of the identical twins is a homosexual, the other is also a homosexual, with a probability of only 20%, so researchers think that environmental factors play a role as well. One of the environmental factors that have been studied is the “brother effect” For every extra brother, the probability of men becoming homosexual