英语学习

短文听写训练 | Why Are There Males and Females?

小白老师2016/11/08英语学习

摘要： 生物界普遍存在的两性系统（雄性和雌性）源于细胞在有性繁殖过程中对线粒体冲突的演化解决方案，其中雌性保留线粒体而雄性放弃，从而避免细胞器间的敌对竞争。

  • 有性繁殖通过结合双亲DNA修复基因缺陷，提升后代健康度。
  • 两性系统限制了可交配对象为种群的一半，看似不利，实则解决细胞内部冲突。
  • 线粒体在融合时会产生激烈对抗，两性分化使一方（雄性）主动放弃线粒体以维持合作。
  • 精子比卵子小的部分原因在于雄性在演化早期已‘缴械’线粒体，由雌性线粒体主导遗传。
  • 若仅有一种性别，每次繁殖都会引发线粒体之间的平等争斗，降低繁殖效率。

小白老师说：从现在开始，量化你的学习，带着任务去听吧！这条两分钟的VOA科技报道，请听三遍：第一遍了解大意；第二遍听写空白处内容；第三遍检查，补全漏听的部分。

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Why are there males and females? Why are there two sexes instead of three, or twelve, or one? On this Moment of Science we’ll learn why two is the magic number.

Let’s start with (1)___________________________. When two organisms reproduce sexually, sperm（精子） and egg（卵子） combine, using DNA from both partners to make offspring（后代）. (2)___________________________________________________.

But why are there two sexes? This means, if you want to reproduce, you can only mate with fifty percent of the population, (3)___________________________________. If there were only one sex you could reproduce with anyone, and it would be easier to find a mate. You’d think this would be an advantage for survival.

As it turns out, lots of other stuff can happen when two cells combine to reproduce. While the DNA in the cells’ nuclei might be happy to join forces（携手合作）, other parts of the cell might not be so pleased with the merger（合并）. (4)____________________________________________________.

(5)____________________________________________________. They would need to fight it out every time. With a two-sex system, (6)____________________________________________________. Male sperm cells are smaller than female eggs partly because (7)____________________________________________________. Female mitochondria（线粒体） always win.

答 案：

  1. why there is sex at all
  2. Combining DNA has a number of advantages, like correcting defects（缺陷） in each parents’ genes, so the offspring are healthier.
  3. making the perfect mate that much harder to find
  4. Specifically, a cell’s mitochondria tend to violently resist merging（合并） with other mitochondria, and feuding（敌对的） mitochondria can turn the DNA’s love feast（节日，盛宴） into a microscopic battlefield.
  5. If there were only one sex, then mitochondria in each reproductive cell would start out on equal footing.
  6. one sex can always unilaterally（单方面地） disarm（缴械）, surrendering（投降） its mitochondria for the sake of easier relations between the sexes
  7. they surrendered this mitochondrial battle long ago

常见问题

为什么生物通常只有两种性别而不是更多？

因为两性系统能有效避免细胞器（如线粒体）在繁殖时发生冲突，一种性别单方面放弃线粒体可维持细胞合作稳定。

雄性精子为何比雌性卵子小？

因为雄性在演化过程中早已放弃传递线粒体，精子只需携带核DNA，结构更精简。

有性繁殖相比无性繁殖有什么优势？

有性繁殖通过混合双亲DNA可修复基因缺陷，提高后代适应性和健康水平。

线粒体在性别演化中起什么作用？

线粒体具有独立DNA且抗拒与其他线粒体融合，两性分化使雌性保留、雄性舍弃线粒体，避免细胞内‘战争’。

参考资料

Why Are There Males and Females? – Moment of Science (VOA)

本文内容基于VOA《科学一刻》节目脚本，解释两性演化的线粒体冲突假说。

The evolution of two sexes: Mitochondrial conflict theory

该理论由演化生物学家提出，认为线粒体遗传冲突是两性系统形成的关键驱动力之一。