标题: 丁丁倒数 78# [打印本页] 作者: 玛莎丁丁 时间: 2012-7-21 01:12 标题: 丁丁倒数 78# Biologist: Some speculate that the unusually high frequency of small goats found in island populations is a response to evolutionary pressure to increase the number of goats so as to ensure a diverse gene pool. However, only the reproductive success of a trait influences its frequency in a population. So, the only kind of evolutionary pressure that can reduce the average size of the members of a goat population is that resulting from small goats achieving greater reproductive success than their larger cousins.
The biologist’s view, if true, provides the most support for which one of the following?
(A) The evolutionary pressure to ensure a diverse gene pool could have the effect of increasing the frequency of a gene for small size. (B) The unusual frequency of small goats in island populations is not a result of the greater reproductive success small goats possess when space is limited. (C) Contrary to what some believe, large goats achieve greater reproductive success than small goats even when space is limited. (D) The evolutionary pressure to ensure a diverse gene pool does not have the effect of increasing the frequency of a gene for small size. (E) A diverse gene pool cannot be achieved in a goat population unless the average size of its members is reduced.作者: simonshen 时间: 2012-7-22 18:47
这题有点搞。我做的话会选D。题目大致是讲：有些人猜测，那岛上的羊个子普遍小，是因为出于进化的压力，要尽量多繁殖以确保基因多样性。但咱的biologist不同意这一观点（however一词可以看出他持反对意见）。他认为，只有（ONLY这个词一定要强调一下）某种特性（这里就是指小个子）在繁殖时候的成功的几率才会影响到它在羊群中所处的比例。换言之，就是因为小个子羊比大个子羊在繁殖中更容易成功，因此才造成了小个子羊占多数。而这个only一词说明这是唯一的解释，所以就排除了“确保基因多样性”作为另一个解释同时存在的可能，也就是说确保基因多样性不是造成小个子羊占多数的原因。所以答案我猜就是D了。作者: 玛莎丁丁 时间: 2012-7-22 23:23
simon君你又出现了！ soga, 所以这题的关键其实是小羊frequency到底与gene diversity和reproductive success of trait之间哪个有关，而evolutionary pressure扰乱视线来的。。。