性,是一件好事
文章来源:未知 文章作者:enread 发布时间:2012-06-01 05:42 字体: [ ]  进入论坛
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Sure, sex may be fun, but it's a lot of work, and the payoff is by no means(绝不) certain. Scientists have speculated for a long time on why all living things don't simply make like amoebas and split. Now a biologist at Michigan Technological1 University has found one good reason: sexual reproduction strengthens an organism's ability to adapt; specifically, it may lead to stronger disease resistance.

Erika Hersch-Green tested the idea on 32 different species of evening primroses3. These native North American wildflowers are unusual in that a number of species reproduce asexually, essentially4 through cloning themselves. That allowed Hersch-Green and her colleagues to compare 16 species that reproduce sexually with an equal number that function asexually(无性地) .

"We found that the sexual plants have an increased ability for adaptive, positive evolution," she said. "That's in line with many of the theories of evolution of sex."

Scientists believe that sexual reproduction(有性生殖) offers two big advantages: It can sweep bad mutations out of the gene5 pool more quickly. Also, by shuffling6 parents' genetic7 material each generation, it increases the likelihood that new genetic combinations will arise that help organisms adapt to their environment.

To find evidence of those good genetic recombinations, Hersch-Green and her team sequenced the gene chitinase (pronounced KIE-tin-ace) A in each of the 32 species. All plants have the gene, which makes the enzyme8 chitinase and helps them identify and fight off diseases such as powdery mildew9. However, the genes10 are not exactly the same; there are some differences in their building blocks, called nucleotides, which means that there are slight variations in chitinase from species to species.

Once they knew the sequence of nucleotides(核苷酸) in the gene for each species, the researchers compared them using well-established mathematical models. They found that the chitinase A genes in the evening primrose2 species that reproduce sexually were different in four places from the ancestral gene, while the genes in the asexual species had not changed. In addition, the genes in the sexual plants had a higher expression level, meaning they produced more of the chitinase enzyme used to fight off disease.

She also looked at how well 12 different genotypes of the same asexual evening primrose species weathered attacks by powdery mildew. Those that sustained the most damage from the mildew also were less fit, meaning they produced fewer fruits. "This suggests that common pathogens of evening primrose plants are an important selective agent for these plants," Hersch-Green said. "Furthermore, molecular11 changes that increase chitinase expression and reduce disease damage are likely to be very good for the plants."

"This is in line with the theory that sex provides an evolutionary12 advantage to organisms," Hersch-Green said. "Until now, there had been no empirical evidence to support this advantage of new genetic combinations."

The findings are published in the article "Adaptive Molecular Evolution of a Defence Gene in Sexual but not Functionally13 Asexual Evening Primroses," published May 15 online in the Journal of Evolutionary Biology. Coauthors on the study are H. Myburg of North Carolina State University and M. T. J. Johnson of the University of Toronto at Mississauga.



点击收听单词发音收听单词发音  

1 technological gqiwY     
adj.技术的;工艺的
参考例句:
  • A successful company must keep up with the pace of technological change.一家成功的公司必须得跟上技术变革的步伐。
  • Today,the pace of life is increasing with technological advancements.当今, 随着科技进步,生活节奏不断增快。
2 primrose ctxyr     
n.樱草,最佳部分,
参考例句:
  • She is in the primrose of her life.她正处在她一生的最盛期。
  • The primrose is set off by its nest of green.一窝绿叶衬托着一朵樱草花。
3 primroses a7da9b79dd9b14ec42ee0bf83bfe8982     
n.报春花( primrose的名词复数 );淡黄色;追求享乐(招至恶果)
参考例句:
  • Wild flowers such as orchids and primroses are becoming rare. 兰花和报春花这类野花越来越稀少了。 来自《简明英汉词典》
  • The primroses were bollming; spring was in evidence. 迎春花开了,春天显然已经到了。 来自互联网
4 essentially nntxw     
adv.本质上,实质上,基本上
参考例句:
  • Really great men are essentially modest.真正的伟人大都很谦虚。
  • She is an essentially selfish person.她本质上是个自私自利的人。
5 gene WgKxx     
n.遗传因子,基因
参考例句:
  • A single gene may have many effects.单一基因可能具有很多种效应。
  • The targeting of gene therapy has been paid close attention.其中基因治疗的靶向性是值得密切关注的问题之一。
6 shuffling 03b785186d0322e5a1a31c105fc534ee     
adj. 慢慢移动的, 滑移的 动词shuffle的现在分词形式
参考例句:
  • Don't go shuffling along as if you were dead. 别像个死人似地拖着脚走。 来自英汉文学 - 嘉莉妹妹
  • Some one was shuffling by on the sidewalk. 外面的人行道上有人拖着脚走过。 来自英汉文学 - 嘉莉妹妹
7 genetic PgIxp     
adj.遗传的,遗传学的
参考例句:
  • It's very difficult to treat genetic diseases.遗传性疾病治疗起来很困难。
  • Each daughter cell can receive a full complement of the genetic information.每个子细胞可以收到遗传信息的一个完全补偿物。
8 enzyme cPozF     
n.酵素,酶
参考例句:
  • Above a certain temperature,the enzyme molecule will become unfolded.超过一定温度,酶分子将会展开。
  • An enzyme that dissolves the fibrin of blood clots.能溶解血凝块中的纤维的酶。
9 mildew 41oyq     
n.发霉;v.(使)发霉
参考例句:
  • The interior was dark and smelled of mildew.里面光线很暗,霉味扑鼻。
  • Mildew may form in this weather.这种天气有可能发霉。
10 genes 01914f8eac35d7e14afa065217edd8c0     
n.基因( gene的名词复数 )
参考例句:
  • You have good genes from your parents, so you should live a long time. 你从父母那儿获得优良的基因,所以能够活得很长。 来自《简明英汉词典》
  • Differences will help to reveal the functions of the genes. 它们间的差异将会帮助我们揭开基因多种功能。 来自英汉非文学 - 生命科学 - 生物技术的世纪
11 molecular mE9xh     
adj.分子的;克分子的
参考例句:
  • The research will provide direct insight into molecular mechanisms.这项研究将使人能够直接地了解分子的机理。
  • For the pressure to become zero, molecular bombardment must cease.当压强趋近于零时,分子的碰撞就停止了。
12 evolutionary Ctqz7m     
adj.进化的;演化的,演变的;[生]进化论的
参考例句:
  • Life has its own evolutionary process.生命有其自身的进化过程。
  • These are fascinating questions to be resolved by the evolutionary studies of plants.这些十分吸引人的问题将在研究植物进化过程中得以解决。
13 functionally 07b8a8a682798862ca0c3d3a567f4c3d     
adv.机能上地,官能地
参考例句:
  • Objective To explore occlusion reconstruction by computer aided design (CAD) with functionally-generated pathway (FGP). 目的探索借助功能性?记录(functionally-generated pathway,FGP)技术进行口腔固定修复体计算机辅助设计(Computer aided Design,CAD)生理性建?的方法。 来自互联网
  • In this respect, the proceeding was functionally similar to a comparative licensing adjudication. 在这一点上,手续在作用上即类似于比较许可证发放的裁断。 来自英汉非文学 - 行政法
TAG标签: species sexual sex
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