1. Focus. Heredity. Section 4. Section 4

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1 Section 4 Heredity Objectives Before class begins, write the objectives on the board. Have students copy the objectives into their notebooks at the start of class. 1. Focus Warm-Up Quick Quiz Use the clickers to survey student responses. Call on a few volunteers to share their answers to the writing activity. Reiterate any correct ideas they state about dominant traits. Then ask: Why do different people have different forms of the same trait? (They inherit different forms from their parents.) Have the class brainstorm other physical traits that people inherit from their parents. (Sample answers: hair color, eye color, nose shape, body shape) Teaching Transparency W64 Section 4 Objectives Explain how genetic information passes from one generation to the next. Identify the causes of genetic disorders. Compare the role of genes, environment, and behavior in affecting a person s risk for disease. Vocabulary heredity chromosome gene genetic disorder Heredity Quick Quiz Take a brief self-inventory of some of your physical traits, or characteristics. 1 2 Do you have a widow s peak or a smooth hairline? Do you have free or attached earlobes? Widow s Peak Free Smooth Attached A widow s peak and free earlobes are examples of dominant traits. What do you think a dominant trait is? The Basic Rules of Heredity When a baby is born, people may say, She looks just like her father, or He has his grandmother s ears. Think about how children resemble their parents, grandparents, and other relatives. Their eye color, the shape of their ears, their height these traits are determined in part from the genetic information they inherit from their parents. Heredity is the passing on, or transmission, of biological traits from parent to child. People are similar to each of their parents in some ways but different from their parents in other ways. What determines the combination of traits that are passed on? Chromosomes To answer these questions, you must first learn about chromosomes. Chromosomes (KROH muh sohmz) are tiny structures found within cells that carry information about the characteristics you will inherit. Most of the cells in your body contain 23 pairs of chromosomes 46 chromosomes in all. However, sex cells sperm or eggs contain half this number, or 23 chromosomes. When a sperm and egg unite, the fertilized egg ends up with 46 chromosomes 23 from each parent. 478 Chapter 18 Sensitive Issues Heredity may be a sensitive issue for students who live with adoptive or foster parents. Avoid asking students to talk about traits they share with their biological parents or other biological relatives. Give them the option of using hypothetical examples or other families they know. FYI! Cellular Differentiation All the cells in the human body, except sex cells, are the result of repeated mitotic divisions that began with the single cell that was produced at fertilization. Thus, all the body s cells contain the same genes. As development proceeds, cells become specialized in structure and function. Cells become different, despite having the same genes, because only certain genes are turned on in each cell. Which genes are turned on is due to a complex combination of genetic and environmental factors. 478 Chapter 18

2 2. Teach L3 EL Reading/Note Taking 18-4 Adapted Reading/Note Taking 18-4 Genes Every chromosome in your body is made up of many genes. A gene is a section of a chromosome that determines or affects a characteristic, or trait. Like the chromosomes that contain them, genes come in pairs. Since a sex cell contains only one half of each chromosome pair, it also has only one half of each gene pair. Once a sperm fertilizes an egg, however, the fertilized egg contains two copies of the gene for each trait one from the father and one from the mother. Hereditary information passes from one generation to the next through genes contained on the two sets of chromosomes that a person receives from their parents. Dominant and Recessive Traits Suppose a father has one trait and the mother has another. Which trait will their child have? The answer depends on the makeup of the pair of genes that the child inherits. Consider earlobe shape. Earlobes can be either free or attached. There are two forms, or versions, of the gene for earlobe shape. One form of the gene carries information for free earlobes the dominant trait. A dominant trait is one that appears in an offspring whenever its gene is present. The other form of the gene carries information for attached earlobes the recessive trait. A recessive trait appears in an offspring only when the dominant form of the gene is not present. You need two copies of the recessive form of the gene to have attached earlobes. You need just one dominant form of the gene to have free earlobes. Receiving a dominant form of the gene from both parents will also result in free earlobes. Note that the rules of heredity for most traits, such as height and eye color, are more complex than those for earlobe shape. This is because many different genes plus factors other than genetics affect most traits. Connect to YOUR LIFE Do you get dimples in your cheeks when you smile? Smile dimples are a dominant trait. FIGURE 12 Your looks are determined in part by the traits you inherit. For: Updates on genetic disorders Visit: Web Code: ctn-6184 Reproduction and Heredity 479 The Basic Rules of Heredity Teacher Demo On the board, sketch a sperm and an egg, with 23 chromosomes each, and a cell with 23 pairs of chromosomes, or 46 chromosomes in all. (You can use tick marks to represent the chromosomes.) Use the sketches to explain how fertilization results in a cell with 23 pairs of chromosomes. EL Building Vocabulary Have students find the terms dominant and recessive in an English language dictionary. Ask students to explain the different meanings (in both general usage and in a genetics context) of each term. Then, have them use the terms in sentences that reflect the different meanings. L3 Cooperative Learning Ask students who know about Punnett squares to make and explain a Punnett square for a cross between an Ee mother and an Ee father (Ee Ee), where E represents the dominant gene for free earlobes and e represents the recessive gene for attached earlobes. Ask: What kind of earlobes do the parents have? (free) What possible genetic combinations can the offspring have? (EE, Ee, and ee) Which offspring will have free earlobes? (EE and Ee) Which offspring will have attached earlobes? (ee) Connect to Students may answer yes YOUR LIFE or no. If students are unsure whether they have dimples when they smile, they can ask a classmate. L4 Gifted and Talented Ask interested students to find a family tree that shows the inheritance of a trait through several generations of a real or hypothetical family. (Such trees are available online and in genetics textbooks.) Have some students find a family tree showing a recessive trait and others find one with a dominant trait. Ask students to use their family trees to explain to the class how the traits have been passed from generation to generation. Challenge other students to decide which of the traits are recessive and which are dominant, based on their inheritance patterns. L3 Content Update Use the Web Code to access up-to-date information about genetic disorders. Have students complete the Web activity. Reproduction and Heredity 479

3 Chapter 18, Section 4 Heredity and Disease Visual Learning: Figure 13 Teaching Transparency 54 Guide students in comparing and contrasting the genetic disorders listed in the figure. Ask: Which disorder is the only one listed in the table that is controlled by a dominant gene? (Huntington s disease) Which disorder is the only one caused by abnormal chromosomes? (Down syndrome) Which disorders cause problems with the blood? (sickle cell disease and hemophilia) Which disorders cause brain damage or mental retardation? (Tay-Sachs disease, PKU, and Down syndrome) Call on a student to answer the caption question. Caption Answer Duchenne muscular dystrophy and hemophilia L3 Cultural Connection Point out that several genetic disorders tend to be more common among certain cultures. For example, sickle cell disease occurs more commonly in people with African ancestry. Tay-Sachs is more common among people with Ashkenazi Jewish ancestry. Cystic fibrosis and PKU occur more frequently in people of Northern European ancestry. Genetic Disorders Disorder Type of Disorder Effect on the Body Sickle Recessive disorder High number of red blood cells have an abnormal cell sickle shape; blood cells clump and block small disease blood vessels, causing severe pain and weakness Tay-Sachs disease Recessive disorder Lack of important chemical in the brain results in brain damage and death in childhood Cystic fibrosis Recessive disorder Mucus in lungs becomes thick and sticky, trapping bacteria that cause infections and lung damage; mucus also affects pancreas Phenylketonuria Recessive disorder Body cannot break down phenylalanine, (PKU) a chemical found in food; causes brain damage if not diagnosed and treated early Duchenne muscular Recessive disorder that Lack of important protein needed for muscle dystrophy primarily affects males function leads to loss of muscle control Hemophilia Recessive disorder that Blood does not clot properly, leading to internal primarily affects males bleeding that can damage the joints Huntington s disease Dominant disorder Cells in brain start to die in middle age; mental abilities decline and movements become uncontrollable, resulting in early death Down Chromosomal disorder Mental retardation and heart defects; syndrome characteristic facial features; severity of disease ranges from mild to severe Heredity and Disease Just like earlobe shape, eye color, and other inherited traits, an abnormal condition known as a genetic disorder can be passed from parent to child. Genetic disorders are caused by the inheritance of an abnormal gene or chromosome. FIGURE 13 Genetic disorders may be dominant or recessive, or caused by errors in chromosome inheritance. Reading Tables Name two disorders that are more common in males. Genetic Disorders Figure 13 provides information about some of the more common genetic disorders. Many genetic disorders, such as cystic fibrosis and hemophilia, are recessive traits. A child must receive two abnormal copies of the gene one from each parent in order for the disorder to develop. A few disorders, such as Huntington s disease, are dominant traits. Such disorders require just one abnormal copy of the gene. Other genetic disorders, such as Down syndrome, are the result of too few or too many chromosomes. 480 Chapter 18 FYI! Sun Exposure in Teens Skin cancer is caused mainly by sun exposure during childhood and adolescence. Sunburns at a young age are especially likely to increase the risk of skin cancer. According to a recent survey of more than 10,000 teens nationwide, most teens know that too much sun exposure causes skin cancer, but many continue to deliberately expose themselves to the sun, mainly because of a simple preference for tanned skin. In the same survey, only three in ten teens said they regularly use sunscreen, and eight in ten said they got a sunburn during the past year. 480 Chapter 18

4 Diseases With a Genetic Link You have probably heard that certain diseases run in families. What does that mean? Scientists know that a person s risk for many diseases increases when close relatives have the disease. Some diseases for which a genetic link is suspected or has been identified are breast cancer, colon cancer, high blood pressure, diabetes, and some forms of Alzheimer s disease. How do diseases with a genetic link differ from genetic disorders like those listed in Figure 13? Many different genes affect the development of disease. In addition, those genes do not typically cause disease, but they do increase a person s risk. Connect to YOUR LIFE What diseases run in your family? How can you decrease your risk for these diseases? The Effect of Environment and Behavior Even if you have genes that increase your risk for certain diseases, many other factors also affect your risk. For most diseases, your environment and your behavior affect your risk as much as or even more than your genes. Environmental factors include such things as exposure to air pollution and certain chemicals. The typical climate where you live may be an environmental risk factor. Suppose, for example, that skin cancer runs in your family. Living in a warm, sunny climate would further increase your risk for developing the disease. Exposure to environmental risk factors is sometimes not in your control, especially as a child. Other risk factors, however, are. Among the factors you can control are your habits or behaviors. For example, using sunscreen can reduce your risk of skin cancer. Regular physical activity can lower your risk of high blood pressure, diabetes, and breast cancer. Eating more fruits and vegetables can reduce your risk of colon cancer. Making wise choices now will greatly decrease your risk for disease later on in life. Risk Factors You Can Control Unprotected or excessive exposure to the sun Use of tanning beds Sunburns Risk Factors You Can t Control Fair complexion Multiple or abnormal moles Family history of skin cancer Climate in which you live L1 Special Needs Students may not understand the distinction between genetic disorders and diseases with a genetic link. Make two spider diagrams on the board to show students the difference. Inside one of two large circles write Genetic Disorders, and inside the other write Diseases With a Genetic Link. Draw an arrow, labeled Genes, to the first circle, and draw three arrows, labeled FIGURE 14 Using plenty of sunscreen can reduce your risk of skin cancer. Classifying Which risk factors for skin cancer are genetic? Environmental? Behavioral? Reproduction and Heredity 481 Genes, Behavior, and Environment, to the second circle. Explain the diagrams to the class. Make sure students understand that they can change their behavior and sometimes their environment to reduce their chances of getting diseases with a genetic link. As you make this point, draw X s through the arrows labeled Behavior and Environment. L4 Building Health Skills Analyzing Influences Have some students go online to research risk factors for diseases listed in the text for which a genetic link is suspected breast cancer, colon cancer, high blood pressure, diabetes, some forms of Alzheimer s disease. Ask students to share what they learn with the class. Use what they report to start a class discussion of the relative influences of heredity, environment, and behavior on the risk of developing diseases with a genetic link. L3 Class Discussion Point out that genetic testing saves lives but may have drawbacks. Ask: What might be some drawbacks of genetic testing? (Sample answer: high cost; misuse of the information by employers or insurance companies; coping with the knowledge that you will probably develop a particular disease later in life) Ask students whether they think the drawbacks outweigh the benefits. Connect to Allow students to answer YOUR LIFE this question in their private journals. L3 Visual Learning: Figure 14 Caption Answer: Fair complexion, multiple or abnormal moles, and a family history of skin cancer are genetic risk factors. Living in a warm, sunny climate is an environmental risk factor. Unprotected or excessive exposure to the sun, use of tanning beds, and sunburns are behavioral risk factors. L1 Active Learning To give special needs students a hands-on experience to reinforce concepts of sun protection, bring in several items for them to handle, compare, and evaluate. For example, you might bring in a baseball cap and wide-brimmed hat, or hats made of tightly woven and loosely woven fabrics. Also bring in sun lotions and creams with different SPF values. Have students handle the items and discuss how they protect the body. You may want to encourage students to add their own items from home. Reproduction and Heredity 481

5 Chapter 18, Section 4 3. Assess Evaluate These assignments can help you assess students mastery of the section content. Answers appear below. Teaching Resources Practice 18-4 Section 18-4 Quiz Divide the class into small groups, and have members of each group demonstrate their knowledge of section objectives to one another. Group members should reread passages relating to any objectives for which they have disagreements or uncertainties. L4 Enrich Teaching Resources Enrich 18-4 Health and Community Supporting a Cause Possible organizations students might contact include the Sickle Cell Disease Association of America and the Cystic Fibrosis Foundation. Web sites for the organizations generally give contact information and information about how people can help. Students s should be factually correct and persuasive. FIGURE 15 In the future, blood samples from newborns may routinely undergo genetic testing for both rare disorders and common diseases. Key Ideas and Vocabulary 1. How is genetic information passed from one generation to the next? 2. What are genes? How are they related to chromosomes? 3. What are the causes of genetic disorders? Give two examples of genetic disorders. 4. What three factors influence your risk for disease? Which factors are under your control? Critical Thinking 5. Predicting A man with free earlobes who has two dominant forms of the gene marries a woman with attached earlobes. What kind of earlobes will their children have? Explain. Medical Advances Today, scientists are working hard to develop new ways to identify and treat genetic disorders and diseases with a genetic link. Areas of research include genetic testing and gene therapy. Genetic Testing Genetic testing involves the analysis of a blood sample for the presence of abnormalities in specific genes. Genetic testing has become more common in recent years. The symptoms of some genetic disorders and most diseases don t show up early in life. By knowing someone has the defective gene as early as possible in some cases, even before birth doctors may be able to start therapies that can prevent or reduce future symptoms. Gene Therapy Scientists are currently researching a technique in which healthy copies of a gene are delivered to the cells of a person who has a defective copy of the gene. This therapy would ideally restore normal function to people with a genetic disorder. Unfortunately, gene therapy has yet to be proven as an effective treatment, but the research effort continues. Health and Community Supporting a Cause Contact a local organization that supports research for a genetic disorder. Find out how you can help support the cause. Write an to your friends telling them about the disease, its causes and treatment, and how people can help. 6. Making Judgments Government funding for research of some genetic disorders is very low because the disorders are so rare. Is that reasonable? Explain your position. 7. Evaluating The American Cancer Society estimates that one third of cancer deaths in the United States are due to unhealthy diet and lack of physical activity. Write a paragraph evaluating this statistic. Does it make you feel gloomy or hopeful? Explain. 482 Chapter through genes contained on the chromosomes that a person receives from his or her parents 2. Genes are sections of chromosomes that determine characteristics. Each chromosome contains many genes. 3. Genetic disorders are caused by the inheritance of an abnormal gene or chromosome. Accept any two genetic disorders from Figure 13 on page Genes, environment, and behavior influence your risk. Behavior and sometimes environment are under your control. 5. All of their children will have free earlobes because they will inherit the dominant gene for free earlobes from their father. 6. Students may or may not think it is reasonable. Their explanations should provide logical arguments and show a correct understanding of genetic disorders. 7. Sample answer: The statistic makes me feel hopeful, because it means that I can control the most important risk factors for cancer by eating well and exercising. 482 Chapter 18