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Have you ever heard a news reporter talk about DNA? Reporters talk about DNA found at the scene of a crime. They talk about police finding DNA “fingerprints”. Police sometimes use DNA as a clue to find out who committed the crime.

DNA is a substance (ÎïÖÊ) that makes up genes. Everything alive has genes. Plants have genes. Animals have genes. You have genes.

Genes are the basic units of heredity (ÒÅ´«). Heredity means all the characteristics you inherit from your parents. You get your genes from your parents. You inherit half of your genes from your mother. You inherit half of your genes from your father.

Genes are a kind of code. A tree's genes tell what shape its leaves will be. A cat's genes tell what color its fur will be. Your genes tell what color your eyes will be. Your genes tell what color your hair will be. Everything about you comes from the code in your genes.

Genes line up on strands (Á´) called chromosomes (ȾɫÌå) in cells. Everything alive is made up of cells. Chromosomes are in the center, or nucleus of cells.

Different parts of you are made of different kinds of cells. Your muscles are made of muscle cells. Your skin is made of skin cells. The code in your genes tells your body to make different kinds of cells. The genes in each cell tell the cell how to work. They tell the cell when to make new copies of itself.

An Austrian monk named Gregor Mendel first saw inherited patterns in pea plants. He experimented with pea plants in the 1860s. One of the things, or traits (ÌØÖÊ), Mendel studied was what makes some pea plants tall and some short. He said that the traits must come from units of heredity passed from the parent plants. These units were later called genes.

 In the mid­1990s, scientists discovered that genes are made of DNA. In the 1970s, scientists learned how to change DNA with genetic engineering. Scientists also learned that problems with certain genes cause diseases. Muscular dystrophy, cystic fibrosis, and hemophilia are some genetic diseases£­diseases caused by problems in genes. Today, scientists are looking for ways to cure genetic diseases by changing genes through a process called gene therapy.

21£®What is DNA?

A£®It is a kind of gene.

B£®It is a substance that makes up genes.

C£®It is the basic unit of heredity.

D£®It is a measure to protect crime.

22£®Which of the following about genes is CORRECT according to the passage?

A£®Plants, animals and human beings have the same genes.

B£®Half people inherit all genes from their mothers, others from their fathers.

C£®Genes decide the shapes of a tree's leaves, the color of a cat's fur and our eyes' color as well.

D£®Genes will give us a code when we need it.

23£®Where are genes?

A£®Genes lining up on strands called chromosomes are in the center of cells.

B£®Genes hide in everything alive in our body.

C£®Genes can be nowhere but in our mind, controlling all our actions.

D£®Genes travel in our body and help cope skin, muscle, and eyes.

24£®We can conclude that ________.

A£®scientists were less intelligent than monks in the 1900s

B£®some genes are bad and can cause diseases

C£®we don't need to worry about genetic diseases any longer

D£®the discovery of genes may be of great help in our daily life