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.//

世界上約有60億人。每個人都與眾不同，有些人的眼睛為黑色，有些人的眼睛為褐色。有些人頭發(fā)烏黑，有些人頭發(fā)淺淡。除了人類之外，還有數(shù)以百萬計的其他生物。有些生物微乎其微，是我們無法用肉眼看到的。無論何種生物，每一個都與眾不同。//為什么每個生物都會與眾不同呢？生物的特性又是從何而來？人們的特性是遺傳自母親，還是父親，或是父母雙親？人們從父母所得到的又是哪些特性呢？他們又是如何得到那些特性的呢？生物學(xué)家試圖找到這些問題的答案。一百年前一個叫做門德爾的人所作的研究工作具有特別重要的意義。//門德爾的研究對象是植物，他尤其注重對豌豆植物的研究。他斷定，豌豆植物帶有遺傳因子，父輩植物講這些因子傳給子代植物。今天我們講這些遺傳因子稱為基因。基因是一種將遺傳信息從父代傳給子代的微小物質(zhì)。//依據(jù)門德爾的試驗結(jié)果，生物學(xué)家開始提出了許多問題，例如，我們能否將基因理論運用到人的身上？他們發(fā)現(xiàn)，一個人的基因可以告訴我們這個人的眼睛是褐色的還是藍色的，他的頭發(fā)是烏黑的還是淺色的。現(xiàn)在我們知道每個人都是一個與眾不同的獨特體。//