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Geneticist for a Day

By Jeffrey Weld



ABSTRACT

When studying genetics with my students, it seems to bear fruit when real life applications germane to personal life play center stage. In that spirit, I developed two activities that focus on recent contributions of a couple of real people that my students can identify with- the work of Nancy Wexler and Huntington's Chorea; and the work of Mary Claire-King and the breast cancer gene BRCA-1. The activities are "dry lab" enactments of partial pedigree and genetic analysis studies that allow the kids to walk at least a quarter mile in the shoes of real geneticists. These dry labs lend to extensions using electrophoretic marker simulations and special projects around cell receptors and autoimmunity as well.

SUBJECT OF ACTIVITIES: Human Genetics

GRADE LEVEL: High School biology


INFORMATION FOR THE TEACHER

After conducting pedigrees in groups, students are asked to discuss and compose a document discussing the transmission of the Huntington's gene- dominant or recessive, sex linked, etc. Additionally, they ought to consider Dr. Wexler's own odds for contracting the disease.

Since Dr. Wexler's study was initiated, the location of the huntington's gene, and a DNA marker test for identifying those who carry it, has added great intrigue to the moral/ethical issues surrounding genetic testing. One good source for follow-up is the BSCS blue versions' "supplementary Topics" reader in an article called "The Venezuelan Pedigree Project".

ACTIVITY 1: THE BRCA-1 GENE

INFORMATION FOR STUDENTS

In the last year, the location of a gene responsible for one type of breast cancer has been identified to be the lower right leg of chromosome 15, thanks to a three-year study led by Dr. Mary Claire King at the University of California-Berkeley.

Breast cancer afflicts 2% of women in the U.S., yet it's the leading cause of death. Why? Metastasis! Before growing big enough to be obvious, the cancer spreads into the lymph nodes, and from there, anywhere in the body. By the time it's detected, the cancer has located in numerous organs.

Some forms of breast cancer runs in families. The odds soar from 2% risk nationally to 50% if it is in the family. To identify one's risk, a marker can be pinpointed in DNA analysis, but a family pedigree can determine the need for such a test.

Your Job... Be Mary Claire King for a day!

Here's a dialogue with a patient named Elizabeth, who had a preventive mastectomy at age 28 because of the frequency of breast cancer in her family. (Remember, Dr. King had no inkling as to the hereditary pattern of the BR gene. Here's a tip too, she didn't know it at the outset, but I'll tell you: males can carry the gene and not be affected)

  • "It's my two-year old daughter I'm worried about. Will she get this?"
  • "I married Steven, who has no family history of breast cancer"
  • "I have three sisters, and two already have breast cancer."
  • "Our dad is Frank, who had six sisters (my aunts) one 0f them never showed any signs of breast cancer, though one got ovarian cancer, and three got breast cancer. The other one died in a car accident at age 20."
  • "Franks' parents (my grandparents) are free of breast cancer, but that's as far back as I can go with information."
  • "Franks's sister Rhonda (one of my aunts who had it), married a guy with no family history of it. They had three kids (my cousins), two girls and a boy. One of the girls recently got diagnosed with breast cancer."
  • TRACKING THE GENE...

    First, generate a pedigree as much as possible from the discussion with Elizabeth. From the pedigree, can you determine if the gene is sex linked? Dominant or recessive?

    Then, discuss in a small group, then compile a report which explains the diseases' mode of transmission. Include such explanations as Elizabeth's daughter's likelihood of inheriting the BR gene. Consider such moral issues as testing for the DNA marker, insurance regulations regarding knowledge of the carriers of such markers, and anything else which comes to mind about BRCA-1.

    ACTIVITY 2: WEXLER'S SEARCH FOR THE HUNTINGTON'S GENE

    The year was 1979, and Congress has just issued you the funding to study Huntington's disease- a disorder afflicting more than 50,000 Americans. Very little was known about the inheritance of Huntington's, but Dr. Nancy Wexler (who's mother died of it) knew about the incredibly high rate of the disease around a place called Lake Maracaibo, Venezuela. Here, you'll be a part of a team sent to Lake Maracaibo to study a large family (of more than 5,000 member!), and report your findings!

    The family spans five generations. It is your job (as it was hers) to pedigree the family and see what's going on here!

    Below is a fax that has arrived from Lake Maracaibo...

    To: Dr.s _________________, Pella University, Pella, Iowa from: Huntington's research team, Lake Maracaibo

    Dear scientists,
    What follows are the results of our interviews with 38 members of the Gonzales family. see what you can make of it.
    Sincerely.
    the team

    Generation V:

    Luis, son of Zelda and Ramon. AFFLICTED

    Generation IV:

    Ramon, son of Ricardo and Lydia. AFFLICTED
    Zelda, married to Ramon. HEALTHY
    Felipe, brother of Ramon. AFFLICTED
    Juan, son of Miguel and Letty. AFFLICTED
    Cira, daughter of Miguel and Letty. HEALTHY
    Roberto, son of Miguel and Letty. HEALTHY
    Nora, daughter of Jesus and Margarita, AFFLICTED
    Alejandro, son of Pedro and Beatriz. AFFLICTED
    Delia, daughter of Dano and Andrea. AFFLICTED
    Tio, son of Dano and Andrea. AFFLICTED
    Maria, daughter of David and Guadelupe. AFFLICTED
    Nariza, daughter of David and Guadelupe. AFFLICTED

    Generation III:

    Lydia, daughter of Carlos and Imelda. AFFLICTED
    Ricardo, married to Lydia. HEALTHY
    Helga, daughter of Carlos and Imelda. HEALTHY
    Letty, daughter of Carlos and Imelda. AFFLICTED
    Miguel, married to Letty. HEALTHY
    Margarita, daughter of Carlos and Imelda. AFFLICTED
    Jesus, married to Margarita. HEALTHY
    Beatriz, daughter of Carlos and Imelda. AFFLICTED
    Pedro, married to Beatriz. HEALTHY
    Juanita, daughter Javier and Bonita. AFFLICTED
    Benito, son of Javier and Bonita. HEALTHY
    Dano, son of Chito and Chelita. AFFLICTED
    Andrea, wife of Dano. HEALTHY
    David, son of Chito and Chelita. AFFLICTED
    Guadelupe, wife of David. HEALTHY
    Horatio, son of Chito and Chelita. HEALTHY
    Lucio, son of Chito and Chelita. HEALTHY

    Generation II:

    Imelda, daugher of Rigo and Esmerelda. AFFLICTED
    Carlos, married to Imelda. HEALTHY
    Javier, son of Rigo and Esmerelda. AFFLICTED
    Bonita, married to Javier. HEALTHY
    Chito, son of Rigo and Esmerelda. AFFLICTED
    Chelita, married to Chito. HEALTHY

    Generation I:

    Rigo. AFFLICTED
    Esmerelda. HEALTHY


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