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1、Unit 10 It is in the DNATEACHER: Good morning. Today well talk about an important topic in biology-DNA and DNA testing. Can anybody tell us what DNA stands for? STUDENT 1: deoxyribonucleic acid.TEACHER: Right. Its the molecule that carries genetic information in all living cells. Now first, well loo
2、k at what DNA is and when it was discovered. Then, well look at DNA testing and several applications, or uses of testing. This is an exciting topic for biologists because the more we learn about DNA, the more we see how science may change our lives-from healthcare to our relationships. OK, what does
3、 DNA look like? STUDENT 1: It looks like two strings, kind of wrapping around each other.TEACHER: Yes, exactly. Theres a simple drawing of one in your book. As you can see, a molecule of DNA consists of two strands of chemical compounds arranged in a twisted pattern. Inside the human cell are chromo
4、somes. The DNA is organized in twenty-three pairs of chromosomes in the cell. Genes are arranged on the chromosomes and these carry fundamental genetic information like hair color, eye color, or characteristics that arent as visible, such as intelligence, and a lot more. Scientists have been studyin
5、g DNA for a long time. First, in 1860, Gregor Mendel made two important discoveries: tiny particles he called genes, and, that genes carry information from cell to cell. Now this was really the beginning. Then, in 1953, J. D. Watson and Francis Crick discovered and described the DNA structure. Their
6、 work was so important that they received the Nobel Prize in 1962. For the first time, scientists could understand exactly how DNA tells the cells what to do. This generated more DNA research, and by the end of the twentieth century, scientists made other important discoveries. Probably the most imp
7、ortant work was the Human Genome Project. The goal of the Human Genome Project was to complete the first reading of the human genome, the complete set of human DNA. Uh, this was a huge job, but after ten long years in June, 2000, the head of the Project announced that they had identified the complet
8、e set of human genes. Uh, this was a huge deal. Most people saw this as the beginning of a whole new era in DNA research. Scientists could read all of the genetic messages in the human body! This is, of course, a very brief history of the study of DNA. All right, lets consider DNA testing. One impor
9、tant use of DNA testing is testing identity, which is also called DNA fingerprinting. Heres how a DNA fingerprint is done. Scientists take a small sample of someones hair or skin, which contain DNA. Next, they treat the sample with chemicals and make a film, like a small photograph. On this film the
10、re is a visible pattern of black bars. This pattern of black bars is unique for each person. So, a DNA sample from your hair identifies you, its, its like your fingerprint; it identifies you and you only. I see a question. Miguel? STUDENT 2: Does the DNA from hair or skin or blood all look the same?
11、 TEACHER: No, not exactly. The DNA from your hair will look like hair DNA but it will be uniquely your DNA pattern. Its sort of like all noses look like noses, right? But your nose looks like your nose only. Now I want to look at two applications, or uses, of DNA testing. First, how it can be used b
12、y doctors, and second, how it can be used by the police. Within health-care, one important use is to identify potential for health problems. Researchers have found some genes linked to specific diseases. For example, Huntingtons disease is linked to a defect in chromosome 4, and Alzheimers disease i
13、s linked to a defect in chromosome 19. A genetic link means that doctors know that if someone has defects in these genes, theyre more likely to get these health problems; their potential is increased. Notice, I didnt say “Researchers have found that some gene defects cause specific diseases.” There
14、is simply a link. After doctors perform DNA testing, they can then decide the best way to use the information. For example, they may give medication to a patient to prevent a disease from ever starting. Genetic testing can also be used to decide which medicine to give someone. This is called targete
15、d medicine. To me, this is very exciting and promising. There are tiny differences in DNA from person to person. These differences can affect which patients will be helped by a drug, and who may be harmed by it. This is, uh, a tremendous advantage. It saves lives and money. Now, lets look at how DNA
16、 testing is used by police. The police can use DNA fingerprints to identify and trace criminals. All they need is a small amount, or trace, of blood or hair from the crime scene. If the DNA samples from the crime scene and the suspect match, the results, at least in the United States, can be used as evidence in court. So, DNA testing can be used to help put someone in prison. In much the same way, DNA testing can be used to help innocent people in
