Unit 11D: Practical Report
Introduction
We went to the Natural History Museum to see if the Phenylthiocarbamide gene was present and to
what extent we can taste it. PTC is found in brassica vegetables (e.g broccoli and cabbage) and is a
chemical group. The ability to taste PTC comes from a gene called TAS2R38.
Step 1: Taste test to determine the phenotype
Genotype = An organism's genotype is its genetic structure.
Phenotype = The phenotype is a person's observable characteristics e.g height and eye colour
For me the PTC tastes like paracetamol. I would describe myself as a weak taster because although I
could taste it, it did take a few seconds to kick in and I didn’t think it was the strongest.
The control variable in this experiment was that we all kept in our mouths for the same amount of time
(30 seconds) .We used a control variable so that the experiment was valid and we had the same
amount of time to find out what type of taster we are.
Step 2: Extraction of DNA from cheek cells
1) First, I ran an isotonic solution around in my mouth to collect all the cheek cells; isotonic
solution means it has the same water concentration as the cells. Then I spat it back into the
cup.
2) Next, I put it into an Eppendorf tube and placed it in a microcentrifuge, which is a machine
that spins the fluid at very high speed to separate liquids of different densities. This process
separates the liquid into a heavier layer at the bottom and a lighter layer at the top.
3) Once the liquid was separated, I removed the excess supernatant, and the pellet (cells) was
resuspended in a vortex mixer. The supernatant refers to the liquid floating on the surface,
while resuspension is the process of putting small pieces of solid material back into a gas or a
liquid so they hang or float there.
4) After that, 30μl of the cheek cell liquid was transferred to a tube containing chelex beads.
Chelex beads absorb ions including magnesium, iron, and copper ions, which is crucial
because removing heavy metals lowers the DNA damage when exposed to high
temperatures.
5) We then heated the mixture to 100°C for about 10 minutes, releasing the DNA. Heating
destroys potential enzymes that could damage the DNA and breaks the cell membrane.
6) Finally, we mixed the mixture and placed it into a centrifuge for 90 seconds. Using the
centrifuge is important as it separates the different fractions by density without destroying any
of the cells.
Step 3: Amplify DNA using PCR
Stage Temp. Other info
DNA strands separate 95oC DNA fragments, primers and DNA polymerase places in a vessel in the
thermocycler.
Annealing of primers 55oC Primers join to their complementary bases at the ends of the DNA
fragments.
Introduction
We went to the Natural History Museum to see if the Phenylthiocarbamide gene was present and to
what extent we can taste it. PTC is found in brassica vegetables (e.g broccoli and cabbage) and is a
chemical group. The ability to taste PTC comes from a gene called TAS2R38.
Step 1: Taste test to determine the phenotype
Genotype = An organism's genotype is its genetic structure.
Phenotype = The phenotype is a person's observable characteristics e.g height and eye colour
For me the PTC tastes like paracetamol. I would describe myself as a weak taster because although I
could taste it, it did take a few seconds to kick in and I didn’t think it was the strongest.
The control variable in this experiment was that we all kept in our mouths for the same amount of time
(30 seconds) .We used a control variable so that the experiment was valid and we had the same
amount of time to find out what type of taster we are.
Step 2: Extraction of DNA from cheek cells
1) First, I ran an isotonic solution around in my mouth to collect all the cheek cells; isotonic
solution means it has the same water concentration as the cells. Then I spat it back into the
cup.
2) Next, I put it into an Eppendorf tube and placed it in a microcentrifuge, which is a machine
that spins the fluid at very high speed to separate liquids of different densities. This process
separates the liquid into a heavier layer at the bottom and a lighter layer at the top.
3) Once the liquid was separated, I removed the excess supernatant, and the pellet (cells) was
resuspended in a vortex mixer. The supernatant refers to the liquid floating on the surface,
while resuspension is the process of putting small pieces of solid material back into a gas or a
liquid so they hang or float there.
4) After that, 30μl of the cheek cell liquid was transferred to a tube containing chelex beads.
Chelex beads absorb ions including magnesium, iron, and copper ions, which is crucial
because removing heavy metals lowers the DNA damage when exposed to high
temperatures.
5) We then heated the mixture to 100°C for about 10 minutes, releasing the DNA. Heating
destroys potential enzymes that could damage the DNA and breaks the cell membrane.
6) Finally, we mixed the mixture and placed it into a centrifuge for 90 seconds. Using the
centrifuge is important as it separates the different fractions by density without destroying any
of the cells.
Step 3: Amplify DNA using PCR
Stage Temp. Other info
DNA strands separate 95oC DNA fragments, primers and DNA polymerase places in a vessel in the
thermocycler.
Annealing of primers 55oC Primers join to their complementary bases at the ends of the DNA
fragments.
