Title/Type
Mutations: Genetic Variation Over Time
Summary
Students will investigate the differences that
exist in the DNA sequence of the PTC taste
receptor gene from humans and non human
primates and determine whether the taster
sequence changed to the non-taster or vice
versa. Students will understand that
mutations allow genetic variations to
develop over time and that a close genetic
relationship exists between humans and non
human primates.
Materials
LS (9-11) 3-6; 6a
- computer
- projector
- worksheets and/or workstations
Engage
Ask the class: We have been examining
PTC taste receptor DNA sequences from
two different people. Is it possible to
determine whether the taster sequence
changed to the non-taster or vice versa?
Can you propose a way to determine this?
What species are most closely related to
humans? What data would we need from
non human primates to determine if some
humans have evolved the ability to taste
PTC or lost the ability to taste PTC?
Predict
What can DNA sequence comparisons tell
us about our common ancestor?
Please compare PTC taste receptor DNA
sequences of a human taster, a human non
taster and non-human primates.
Explore
Background Information
Scientists can now compare the PTC
receptor DNA sequence from humans to
that of non-human primates and begin
to determine if humans evolved the
ability to taste bitter compounds or if we
have evolved to be non-tasters
At each of the different locations in the
gene, which human sequence matches the
sequence of non-human primates?
Worksheet or computer workstations
if available.
Explain
Based on the sequence data, can you predict
our “ancestral state” for the PTC taste
receptor? Can you predict if the common
ancestor of humans and non-human
primates had the ability to taste the bitter
compound PTC?
Can you predict if humans have evolved the
ability to taste bitter compounds or have
evolved to be non-tasters?
How does DNA evidence support your
interpretation?
Predict 2
From data presented on DNA sequence of
the PTC taste receptor, is it possible to
determine if bonobos, chimps and gorillas
can taste PTC? Why or why not?
What would scientists need to do to
determine if non-human primates are tasters
or non-tasters?
Explore 2
Taste tests using PTC in non human
primates have been done. Since we cannot
work with non-human primates in class,
studies have shown that chimps also differ
in their sensitivity to PTC.
How is it possible that chimps differ in their
ability to taste PTC if the sequences
examined all match that of human tasters?
What data is missing? Do we have
complete DNA sequences of the PTC taste
receptor gene?
Study the sequence alignments comparing
PTC DNA from human non-tasters, human
tasters and chimps.
What differences do you observe? How
many differences exist between humans
(either taster or non-taster) and chimps?
Can you predict why some chimps do not
taste PTC? How would DNA evidence
Worksheets or workstations if available.
support your prediction?
What experiment or study would you design
to investigate your prediction?
Wrapup