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Activity 4: Genetic Testing


Objective

Students will investigate the impact of carrier screening and prenatal testing.


Background Information

Genetic disorders affect large numbers of people from all racial and cultural groups. Preventive approaches to these disorders are becoming more feasible as scientists gain an understanding of genes and of the causes of genetic disorders. In some cases, the risk that a particular genetic disorder will occur can be assessed before a child is conceived or in the early stages of pregnancy. In other cases, newborns can be screened for a disorder so that appropriate treatment can be started before the condition becomes fatal.

One key to assessing genetic risk for having a child with a particular disorder is carrier testing. This type of testing determines whether the prospective parents are carriers of the gene for the trait. If both the parents are identified as carriers, then there is a 25% chance with each pregnancy that the child will inherit the disease. Carrier testing can also be conducted for X-linked disorders.

One form of prenatal testing involves collecting a sample of fetal cells from the amniotic fluid surrounding the fetus, and testing the fetal DNA to determine if there are chromosomal or special genetic abnormalities. Some types of prenatal diagnosis techniques can be performed as early as nine weeks into the pregnancy. A newer test, known as preimplantation diagnosis, can be performed before in-vitro fertilized cells are implanted in the womb. Prenatal tests are available for hundreds of conditions ranging from mental retardation to late-onset disorders that cause serious mental and physical deterioration in middle age. In about one percent of the cases, prenatal testing may cause complications such as maternal bleeding or fetal death.

Some genetic diseases can be detected at birth by biochemical tests. This type of testing is referred to as newborn screening. Newborn tests are particularly important if the disorder can be treated with interventional therapy.


Materials

For teacher preparation:

  • Small head of red cabbage
  • Cooking pot
  • Distilled water
  • Strainer
  • 2 Bowls
  • Red & blue food dyes
  • White paper coffee filters
  • Scissors

For each pair of students


Preparation

  1. Before class, prepare red cabbage indicator strips. Tear or cut the cabbage leaves into small pieces and place them in a cooking pot filled with distilled water. Boil for five minutes, then allow to cool to room temperature. Pour the cooled cabbage extract through the strainer into a bowl. Soak coffee filters in the solution, and allow them to dry. Cut the dry filters into 1 x 1/2-inch strips and store them a closed container.

  2. Also prepare control indicator strips. Mix red and blue food coloring with distilled water to produce a dye the same color as the red cabbage solution. Soak coffee filters in the solution and allow them to dry. Cut the filters into 1 x 1/2 inch strips and store in a closed container.


Instructions

  1. Have students read the information on cystic fibrosis, then discuss the information with the class. Ask students to think about how they might feel if they knew there was a chance that they could have a child with the disorder.

  2. Divide the class into groups of two. Explain that each group represents a pair of potential parents. Explain to students that they will have the opportunity to test to see if they "carry" the gene for cystic fibrosis. Have each "parental" unit discuss how they feel about being tested. How would they react if they knew they were carriers for cystic fibrosis? Would they want to have children? Why or why not? Ask students to write a brief description of their position.

  3. Mix the red-cabbage indicator strips and control indicator strips together, then hand out one indicator strip to each student. Also have students place a small amount (a tablespoon or so) of vinegar in a paper cup. Explain that the strip represents a blood sample taken from the student. If the student is a carrier for the cystic fibrosis gene, the strip will turn pink when dipped in the vinegar. If the student is not a carrier for the gene, the strip will not change color.

  4. Have students put a drop of vinegar onto their indicator strips and record the results. Then ask each "couple" to determine the chances of having a child with cystic fibrosis. Have students discuss how they feel about the results of the test.

  5. Next, ask students in each pair to imagine that they are a couple expecting their first baby. This time provide each pair with a single strip of indicator paper. Explain that this strip represents the genetic makeup of the couple's "fetus." If the strip turns pink, the fetus has cystic fibrosis. Once again have each couple write a brief description about how they feel about the testing and the results.


Discussion Questions

  1. Do you think carrier testing is a good idea? Why or why not? Do you think prenatal testing is a good idea? Why or why not?

  2. Should genetic screening for lethal diseases be mandatory? Why or why not?

  3. How would you feel if you knew there were genetic tests for traits, such as stature, physical appearance, or mental ability? Would you take such a test? Why or why not? Who should determine which traits are "desirable" and which are "undesirable?"

  4. What is the relationship between genetic testing for a disorder and curing the disorder? Would the availability of a cure for a disorder affect your desire to be tested? Explain your answer.

  5. Suppose that scientists knew the function of every human gene and were able to test for each trait. For what genetic characteristics, if any, would you want to test an embryo? Which characteristics, if any, might make you decide not to have children or to terminate a pregnancy? Why?


Extensions

  1. Divide the class into groups and supply each group with the Genetic Disorder Profiles and Organizations page. Ask the groups to read the profiles. Then ask them to make a list showing the disorders for which they would consider being tested and the disorders for which they would consider testing a fetus or newborn. Have groups present their lists and discuss the reasons for their choices.

  2. Divide the class into groups and have each group choose one of the disorders listed in the Genetic Disorder Profiles and Organizations. Then have them research news articles and other sources for further information about the disorder. (You may want them to contact one of the organizations listed for more information.) Ask the groups to write two editorials--one presenting the pros of testing for the disorder and another presenting the cons. Have students share their editorials with the class, and discuss their positions.

  3. Have teams of students explore the potential implications of genetic testing by having them research different tests currently used to detect latent or hidden conditions. Ask students to make a brief oral presentation of their findings.


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