America's Stone Age Explorers
To learn how mitochondrial DNA (mtDNA) is inherited.
- copy of the "The Hunt for mtDNA" student handout
Because mtDNA is only passed down along maternal lines and mutates at
predictable rates, it has been used to help trace migration routes of early
humans. In this activity, students will learn how mtDNA gets passed along
To set up the activity, tell students that they will be working as forensic
scientists to help solve a long-standing "missing persons" case. 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).
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 people, which living relatives would be eligible to donate their mtDNA
for comparison? (Mitochondrial DNA can be retrieved from exhumed remains, but
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.
Mitochondrial DNA cannot be retrieved from cremated remains.) The missing
person is labeled with a question mark in the pedigree chart.
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? How far back can mtDNA of an
individual be traced?
As an extension, have students research how mtDNA has been used to trace
migratory routes of early humans.
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. Mitochondrial DNA 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
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?
Mitochondrial DNA could be used to confirm that two brothers with the same
mother who died in a crash were related, but not to distinguish the brothers'
remains from each other in the way that nuclear DNA could. In theory, mtDNA
could be traced back to the first "mitochondrial Eve," a woman whom scientists
have tried to pinpoint. However, controversy exists regarding the usefulness
and accuracy of molecular clocks used to date when a mitochondrial Eve might
have lived. (Molecular clocks are based on assumptions about how regularly DNA
NOVA Web Site—America's Stone Age Explorers
In this companion Web site to the program, consider who or what killed off the
mammoths and other megafauna 13,000 years ago, view a gallery of images of
Clovis artifacts, peruse an Ice Age North American map to learn more about
pre-Clovis sites, and match Stone Age artifacts to their uses.
Center for the Study of the First Americans
Contains articles on theories regarding the peopling of North America.
Clovis and Beyond
Includes articles on possible coastal migration routes and the Solutrean-Clovis
Jim and Jake Page.
The First Americans: In Pursuit of Archaeology's Greatest Mystery.
New York: Random House, 2002.
Challenges the theory that the Clovis people were the earliest settlers of the
Dixon, James E.
Bones, Boats, and Bison.
Albuquerque: University of New Mexico Press, 1999.
Argues that the earliest humans in North America were not big-game hunters
following mammoths across the Bering Land Bridge but rather general foragers
colonizing the New World.
In Search of Ice Age Americans.
Salt Lake City: Gibbs Smith, 2002.
Draws on fieldwork worldwide to try to reconstruct the daily lives of the
The "Hunt for mtDNA" activity aligns with the following
National Science Education Standards:
Science Standard C:
Reproduction and heredity:
Science Standard C:
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.
Classroom Activity Author
classroom activity originally appeared in a slightly different form in the
companion Teacher's Guide for NOVA's "Last Flight of Bomber 31" program.