Every living cell(细胞)contains genes(基因).⑴They are too small to be seen in a microscope,but they are vitally important,each set of genes in the body contains all the instructions needed to make a human being.Some genes determine hair color.Some determine the shape of a nose.Some genes help determine your height and even your weight. ⑵ Genes are made of a chemical called DNA—the letters stand for deoxyribonucleic acid.In the early 1950's,two scientists.Francis Crick and James Watson,figured out how the parts of DNA fit together. ⑶Once scientists understood this structure,it became possible to take pieces of DNA apart and put them together in new ways.New kinds of genes could be made in this manner.
Scientists have studied the genes of many plants and animals. ⑷They have worked out which genes affect the color of a tomato and the thickness of its skin.Working out which genes determine which features is called genetic mapping,scientists have begun the Human Genome Project,an ambitious effort to map all the genes in the human body.
Some genes may be defective.For example,something might be wrong with the gene that makes blood clot(凝聚). ⑸An individual born with this defective gene could suffer serious hemorrhages(出血)or even bleed to death because his or her blood fails to clot.If scientists ever child has any defective genes.They might even discover how to treat these genes before the child is born.
Scientists have studied the genes of many plants and animals. ⑷They have worked out which genes affect the color of a tomato and the thickness of its skin.Working out which genes determine which features is called genetic mapping,scientists have begun the Human Genome Project,an ambitious effort to map all the genes in the human body.
Some genes may be defective.For example,something might be wrong with the gene that makes blood clot(凝聚). ⑸An individual born with this defective gene could suffer serious hemorrhages(出血)or even bleed to death because his or her blood fails to clot.If scientists ever child has any defective genes.They might even discover how to treat these genes before the child is born.
Key:
⑴基因太小，即使在显微镜下也难以看到，但是他们却至关重要，每组人体基因都含有构成人体生命所需要的信息。
⑵基因又称之为DNA化学物质组成－DNA代表脱氧核糖核酸。
⑶一旦科学家懂得了其结构，就有可能分离DNA并使之重新组合。
⑷他们已经解答出哪种基因影响着西红柿的色泽和其外皮的厚度。
⑸一位生来就有基因缺陷的人可能患有严重出血症，甚至血流而死，因为血液无法凝结。
