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  3. Sexual Reproduction Birds do it. Bees do it. But d

Sexual Reproduction Birds do it. Bees do it. But d

游客2023-12-26  58
问题                            Sexual Reproduction
   Birds do it. Bees do it. But dandelions don’t. The prodigious spread of these winsome weeds underscores a little-appreciated biological fact. Contrary to human experience, sex is not essential to reproduction. Asexual organisms can often churn out multiple generations of clones, gaining a distinct edge in the evolutionary numbers game. And therein lies the puzzle: If sex is such an inefficient way to reproduce, why is it so widespread?
   Sex almost certainly originated nearly 3. 5 billion years ago as a mechanism for repairing the DNA of bacteria. Because ancient earth was such a violent place, the genes of these unicellular organisms would have been frequently damaged by intense heat and ultraviolet radiation. " Conjugation" — the intricate process in which one bacterium infuses genetic material into another — provided an ingenious, if cumbersome, solution to this problem, although bacteria continued to rely on asexual reproduction to increase their numbers.
   Animal sex, however, is a more recent invention. Biologist Lynn Margulis of the University of Massachusetts at Amherst believes the evolutionary roots of egg and sperm cells can be traced back to a group of organisms known as rotests that first appeared some 1. 5 billion years ago.(Modern examples include protozoa, giant kelp and malaria parasite. ) During periods of starvation, Margulis conjectures, one rotest was driven to devour another. Sometimes this cannibalistic meal was incompletely digested, and the nuclei of prey and predator fused. By joining forces, the fused cells were better able to survive adversity, and because they survived, their penchant for union was passed on to their distant descendants.
   From this vantage point, human sexuality seems little more than a wondrous accident, born of a kind of original sin among protozoa. Most population biologists, however, believe sex was maintained over evolutionary time because it somehow enhanced survival. The mixing and matching of parental genes, they argue, provide organisms with a novel mechanism for generating genetically different offspring, thereby increasing the odds that their progeny could exploit new niches in a changing environment and, by virtue of their diversity, have a better chance of surviving the assaults of bacteria and other tiny germs that rapidly evolve tricks for eluding their hosts’ defenses. [br] Which statement is NOT true about conjugation?
选项 A、Conjugation is a process whereby the genes of bacteria are transferred.
B、Conjugation is a process whereby the genes of bacteria are recombined.
C、Conjugation is a process whereby the genes of bacteria are repaired.
D、Conjugation is a process whereby the genes of bacteria are damaged.
答案 D
解析 概念主旨题型，答案是D。此题考查对conjugation这一概念的理解。原文第三段将其描述为“the intricate process in which one bacterium infuses genetic material into another”(一个细菌将遗传物质注入另一个细菌的微妙过程)。选择项并未照搬原文文字，因此需基于原文的描述把握概念的实质。给出的四个选择项分别为：在这个过程中，细菌的遗传因子A“发生转移”、B“进行重组”、C“得到修复”、D“遭到损害”。A、B选项涉及过程描述，从定义本身可推定此两选项无误。C、D选项涉及结果／后果描述，从上下文可知，远古地球生存环境恶劣，细菌遗传因子常因高热和紫外线辐射而遭受损害，conjugation则提供了一种解决方案，可见结果应当是细菌的遗传因子得到修复，C选项描述无误。正确答案应为D。本题核心：1．注意题干是以否定形式出现的，要求选出的是描述不正确的选项；2．不可因原文中出现damage原词而断章取义将其视为正确理解，而应围绕正确的逻辑关系作答。
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