There are about six billion people in the world. But every person is unique. Some people have black eyes; others have brown eyes. Some have dark hair, others have light hair. Besides humans, there are millions of other living creatures. Some are so tiny that we simply can’t see them with our own eyes. Whatever it is, every living creature is different from every other.// Why is each living thing unique? Where do its characteristics come from? Do people receive characteristics from their mothers or fathers, or both? Which characteristics do they receive? How? These are some of the questions that biologists try to answer. The work of a man by the name Mendel a hundred years ago was especially important.//Mendel studied plants, especially pea plants. Mendel decided that pea plants carried factors, and parents passed these factors onto their offspring. Today we call these factors genes. Genes are tiny pieces of matter that carry information from parents to offspring. // Based on Mendel’s work, biologists began to ask such questions as “Can we apply our information about genes to people?” they discovered that in a person genes told whether he would have brown eyes or blue eyes, whether he would have dark hair or light hair. Now we know that every person is unique.//

世界上约有60亿人。每个人都与众不同，有些人的眼睛为黑色，有些人的眼睛为褐色。有些人头发乌黑，有些人头发浅淡。除了人类之外，还有数以百万计的其他生物。有些生物微乎其微，是我们无法用肉眼看到的。无论何种生物，每一个都与众不同。//为什么每个生物都会与众不同呢？生物的特性又是从何而来？人们的特性是遗传自母亲，还是父亲，或是父母双亲？人们从父母所得到的又是哪些特性呢？他们又是如何得到那些特性的呢？生物学家试图找到这些问题的答案。一百年前一个叫做门德尔的人所作的研究工作具有特别重要的意义。//门德尔的研究对象是植物，他尤其注重对豌豆植物的研究。他断定，豌豆植物带有遗传因子，父辈植物讲这些因子传给子代植物。今天我们讲这些遗传因子称为基因。基因是一种将遗传信息从父代传给子代的微小物质。//依据门德尔的试验结果，生物学家开始提出了许多问题，例如，我们能否将基因理论运用到人的身上？他们发现，一个人的基因可以告诉我们这个人的眼睛是褐色的还是蓝色的，他的头发是乌黑的还是浅色的。现在我们知道每个人都是一个与众不同的独特体。//