Title/Type
Mutations: The effect on phenotype
Summary
Investigate the differences that occur
between DNA sequence that codes for the
PTC taste receptor gene and relate the
information to differences in phenotype - in
this case, the ability to taste PTC.
LS (9-11) 1.2: 2b & 2c
Materials
- computer
- projector
- worksheets and/or workstations
- PTC and control taste strips
Engage
Provide students with control taste strips.
Ask students to place this first strip of paper
in their mouths. Ask -What do you taste?
Ask students to place the second strip of
paper (containing PTC) in their mouths.
Ask –
-What do you taste?
Are we all able to taste a bitter compound?
How many can taste PTC?
How many cannot taste PTC?
What percentage of people in the class are
tasters?
How is it possible that we taste things
differently?
Explore
Background Information
For many years, scientists have studied
how and why the ability to taste certain
compounds differs from person to person.
In the 1930’s scientists discovered that
some people can taste a bitter compound
known as PTC (phenylthiocarbamide),
while others cannot. In order to taste
something, a receptor on the tongue bindsi
a specific chemical in food. When the
chemical binds to the receptor, a signal is
sent to the brain where it is interpreted as
a particular taste—sour, bitter, sweet,
salty or umami.
Recently, the gene that codes for the
receptor that binds PTC was identified
and its DNA sequence determined.
Researchers have identified three
nucleotide positions that vary within the
human population. Sequence
differences at these three contribute to
the ability or inability to taste PTC.
Engage
Ask the class: Please examine the DNA
sequences from two different people: “NT”
and “TR.” The sequences you are
examining code for a taste receptor that
allows people to taster a bitter compound –
called phenylthiocarbamide – or PTC. Are
the sequences identical? If not, how many
differences can you identify? At what
nucleotide positions are these differences
located?
Predict
How might the differences in DNA
sequence affect the taste receptor protein?
Students will transcribe and translate DNA
sequences, one from TR; the other from NT
to determine if the resulting amino acids
differ.
How many differences are found in the
amino acid sequences of “TR” and “NT”?
Explore
Explain
Worksheet with projector, or computer
workstations if available.
Students use worksheets for
transcription activity.
How could these differences affect the
function of the protein?
How can we test if TR and NT differ in
their ability to taste PTC?
Why would it be beneficial to have the
ability to taste PTC?
Could it be harmful to not be able to taste
PTC? Why?
Could it be beneficial to not taste PTC?
TR = taster; NT = non-taster
Wrapup
Please note: Several of these activities can be strung together, even within a class period;
so they can be short, or not.