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Last Flight of Bomber 31

Classroom Activity


Objective
To identify which members of a family share the same mitochondrial DNA (mtDNA).

Materials for each team
  • copy of "The Hunt for mtDNA" student handout (PDF or HTML)
  • colored pencil or pen
Procedure
  1. Tell students that they will be working as forensic scientists to help solve a long-standing "missing persons" case.

  2. Provide each team with a copy of "The Hunt for mtDNA" student handout. Explain to students what mtDNA is, how it differs from nuclear DNA, and how it is inherited (see Activity Answer for more information).

  3. Set up the challenge: An anthropologist has found a few human bones at a site in South Africa. Investigators think they might belong to a Nobel Prize-winning dung beetle biologist who disappeared in Africa. Since the bones have been exposed to severe weather for many years, the only DNA that may be salvageable is mtDNA. Investigators have compiled a pedigree chart that lists all the missing person's relatives. But investigators are having problems identifying his maternal relatives. Which of the people in the "Who's Related by mtDNA?" pedigree chart carry the great-great grandmother's mtDNA, and of those, which living relatives would be eligible to donate their mtDNA for comparison? (mtDNA can be retrieved from exhumed remains; however, this is a costly process and can be emotionally difficult for families. When possible, it is always best to retrieve mtDNA from a living relative. mtDNA cannot be retrieved from cremated remains.) The missing person is labeled with a question mark in the pedigree chart.

  4. After students have completed the challenge, discuss their results. What do students conclude about the inheritance patterns of mtDNA? Why aren't the dung beetle biologist's children eligible for testing?

  5. As an extension, have students research how mtDNA has been used in real-life forensic investigations.

Activity Answer

Everyone carries two types of DNA: nuclear DNA, found in the nucleus of each body cell, and mitochondrial DNA (mtDNA), found in the mitochondria located in the cell's cytoplasm outside the nucleus. Nuclear DNA codes for most proteins made by the cell and is responsible for the inheritance of physical traits, such as hair color or whether a person has dimples, as well as inherited genetic disorders, such as sickle cell anemia or Tay-Sachs disease. MtDNA codes for its own proteins and for ribosomal and transfer RNAs.

During reproduction, the father's sperm cell—which contains both nuclear DNA and mtDNA—donates only its nuclear DNA to the zygote that results from the fusion of the sperm with an egg cell. (Some researchers argue that a fragment of the father's mtDNA is in fact passed on, though it represents much less than 1 percent of the total.) Therefore, all the DNA in a person's mitochondria comes from his or her mother. This means that each new generation has only the mtDNA of the mother, who has only the mtDNA of her mother, and so on. (Males have only the mtDNA of their mothers as well but do not pass it on.) As a result, mtDNA samples can be used to identify any maternally related individuals.

The people related to the missing person's maternal grandmother (who are the candidates for getting mtDNA to compare to that of the missing person), are connected with heavy lines in the pedigree chart below. The 10 living relatives eligible for testing are shaded.

Who's Related by mtDNA? Answer chart MtDNA could be used to confirm that two brothers with the same mother who died in a crash were related, but not used to distinguish their remains from one another in the way that nuclear DNA could. Because mtDNA molecules are present in thousands of copies per cell (compared to nuclear DNA, which is present in only two copies per cell), mtDNA is more likely to be found in small or degraded samples than is nuclear DNA. In addition, environmental factors, such as prolonged exposure to the elements, often destroy nuclear DNA.

Links and Books

Book

Garfield, Brian, and Terrence Cole. The Thousand-Mile War: World War II in Alaska and the Aleutians.
Fairbanks: University of Alaska Press, 1995.
Uses U.S. and Japanese records, personal stories, letters, and diaries of participants to tell the story of the battles fought in Alaska and the Aleutians.

Article

Wetterman, Ralph. "One Down in Kamchatka." The Retired Officer Magazine, January 2001.
Tells the story of Bomber 31 and the efforts to recover and identify crew members' remains.

Web Sites

NOVA's Web Site—Last Flight of Bomber 31
www.pbs.org/nova/bomber/
In this companion Web site to the NOVA program Last Flight of Bomber 31, view ten classic American bombers, find out about the U.S. effort to bring home all MIAs, take a visual tour of Kamchatka, and learn how mitochondrial DNA is used to trace kinship.

History of WWII in the Aleutians
www.nps.gov/aleu/WWII_in_the_Aleutians.htm
Provides a chronology and description of the Aleutian Campaign.

U.S. Army Central Identification Laboratory
www.cilhi.army.mil/
Shows how the lab searches for, recovers, and identifies missing personnel from World War II, the Korean War, the Cold War, and the Vietnam War.

Wars and Conflict: World War II
www.bbc.co.uk/history/war/wwtwo/index.shtml
Provides a summary of World War II from 1939 to 1945.

Standards

The "Hunt for mtDNA" activity aligns with the following National Science Education Standards.

Grades 5-8

Life Science

Science Standard C:
Life Science

Reproduction and heredity

  • Reproduction is a characteristic of all living systems; because no individual organism lives forever, reproduction is essential to the continuation of every species. Some organisms reproduce asexually. Other organisms reproduce sexually.

Grades 9-12

Life Science

Science Standard C:
Life Science

The molecular basis of heredity

  • In all organisms, the instructions for specifying the characteristics of the organism are carried in DNA, a large polymer formed from subunits of four kinds (A, G, C, and T). The chemical and structural properties of DNA explain how the genetic information that underlies heredity is both encoded in genes (as a string of molecular "letters") and replicated (by a templating mechanism). Each DNA molecule in a cell forms a single chromosome.

Teacher's Guide
Last Flight of Bomber 31
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