Question

Every living cell contains genes. They are too small to be seen in a microscope, but they are very 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.

Genes are made of a chemical called DNA-the letters stand for deoxyribonucleic acid(脱氧核糖核酸). In the early 1950's, two scientists, Francis Crick and James Watson, figured out how the parts of DNA fit together. Once 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. They 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(有缺陷的). For example, something might be wrong with the gene that makes blood clot(凝聚). A baby 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 learn how to map all the genes in our bodies, they can determine whether or not an unborn child has any defective genes. They might even discover how to treat these genes before the child is born.

1.What was the achievement of Francis Crick and James Watson?

A. They discovered why people have different hair colors.

B. They learned that some people bleed for long periods of time.

C. They looked at human cells under the microscope.

D. They worked out the structure of DNA.

2.What is the main idea of this passage?

A. Defective genes can never be repaired.

B. Genes are too small to be seen through a microscope.

C. Genes help scientists understand how living things develop their characteristics.

D. The Human Genome Project may explain the role of every gene in the body.

Answer 1

1.D

2.C

【解析】

试题分析：每一个活的细胞都含有基因，它们虽然很小，但却非常重要。基因是带有遗传信息的DNA片段，DNA是脱氧核糖核酸的缩写。一些基因决定头发的颜色，一些决定鼻子的形状，一些决定一个人的身高甚至体重。

1.two scientists, Francis Crick and James Watson, figured out how the parts of DNA fit together”可知，Francis Crick和James Watson弄清楚了DNA的结构，故选D。

2.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.”可知，文章主要讲的是基因能够帮助科学家了解生物的性格特征是怎样发展的，故选C。

考点：科学类短文阅读