PTC Assessment-Student Version
ARISE Curriculum.
PTC Lab Inquiry-based Assessment
S. Gell draft 5 2.2.1
In the PTC lab we examined natural variation in a human gene for tasting
PTC. Use what you learned in this laboratory exercise to help you answer
questions about guppies and their ability to see colored patterns.
Guppies are small fish that live in warm fresh water. Male guppies are
known for their brightly colored patterns. These patterns are thought to be
important for mate choice, with females preferring males that have bright
and unusual coloring patterns1.
”Sexy” Male Guppy (Image from Ref 1)
Q1: For a male guppy, what would be one a major advantage and one
major disadvantaged of having very brightly colored tails in the wild?
[Broad area 1.1]
Scientists studying guppy behavior noticed that the females needed to
be able to detect Ultra-Violet (UV) light to make decisions about the
quality of the markings on males2. Humans cannot see colors in this range,
but many animals can. In order to detect UV light, animals must have a
UV-light receptor in their eye. This receptor gene is called opsin. Scientists
sequenced the opsin gene from two related species of guppies.
The genomic sequence for part of the UV-light receptor (opsin) for the
two guppy species is below.
Species 1: P.reticulata
CTG GTT TGC TGG ACA CTT TAC GCC AGT GTA GCC TGG TAC ATC TTC TCA AAT CAG
___________________________________________________________________
Species 2: G. holbrooki
CTG GTT TGC TGG ATA CCT TAC GCC AGT GTG GCC TGG TAC ATC TTC ACA CAT CAG
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PTC Assessment-Student Version
Q2: [LS1(9-11)-2a,c]
A. Translate each DNA sequence into an amino acid sequence using your
codon table. Write the answer on the line provided below the sequence.
B. Circle any coding changes in the amino acid sequence.
C. Put a box around any silent or non-coding changes in the DNA
sequence.
Q3: A light receptor, like a taste receptor, is used to sense a particular
signal and then transmit that information to the brain. How might
changes to amino acid sequence effect a light receptor? [LS1(911)FAF+POC-2b]
Q4: You noticed that sequence TTCTCA (P. reticulata) is recognized by
the restriction enzyme FshI, but the sequence to TTCACA in G. holbrooki is
not.
A. How could you use the restriction enzyme FshI to distinguish between
samples of DNA from these two species?
Q5. You have discovered a new population of guppies and want to
determine if the opsin gene in this population has the same
polymorphisms (nucleotide changes) as the other species.
A. Explain how the FshI enzyme could be used to help you determine this.
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PTC Assessment-Student Version
A1. If the restriction enzyme cuts the DNA from fish in the new population
of guppies, can you be confident that the fish carry the P. reticulata
allele? If the enzyme does not cut the DNA what does that tell you about
the DNA sequence?
B. (II, CC) Starting with DNA isolation describe the 4 major steps in this
experiment and briefly explain why you need to do each.
1. DNA isolation –
2.
3:
4.
C. After you cut the DNA with FshI what would you expect to see if the
new population contained fish that were homozygous for the P. reticulata
allele? For the G. holbrooki allele? What would you see if there were
heterozygous fish?
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PTC Assessment-Student Version
D. What controls would you include in this experiment to show the
genotypes of fish from the new population of guppies? [Broad Area 2.5]
Q6: You tested 6 individuals from the new population of guppies. Based
on the data below determine if each individual is homozygous for the P.
reticulata allele (P/P) or the G. Holbrooki allele (G/G) or is heterozygous for
the two alleles (G/P) [Broad area 3.10, LS1(9-11)-2b, LS3(9-11)-7a]
U = uncut (not digested with FshI), C = cut (digested with FshI)
Genotype of individual samples. (G/G, P/P G/P)
1. ___
2. ___
3. ___
4. ___
5. ___
6. ___
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PTC Assessment-Student Version
Q7: Following your observation that different populations of guppies have
different alleles of the opsin gene, you want to determine which allele
represents the ancestral state of the guppy opsin gene. How might you do
this? [Broad area 2.4, LS3(9-11)-6a]
Q8: By looking at the data below, determine which allele (P. reticulata or
G. holbrooki) is most likely the ancestral state of the guppy opsin and
explain how the data supports your hypothesis. [Broad area 1.2 and 4.12,
LS3(9-11)-8d]
Common ancestor
Zebrafish
G. holbrooki
P. reticulata
P.reticulata: TGG ACA CTT TAC GCC AGT GTA GCC TGG TAC ATC TTC TCA AAT CAG
G. holbrooki: TGG ATA CCT TAC GCC AGT GTG GCC TGG TAC ATC TTC ACA CAT CAG
Zebrafish*
TGC ATA CTT TAC GCC AGT GTA GCC TGG TAC ATC TTC TCA AAT CAG
Answer here:
Q9: Imagine that P. reticulata live in only clear, fast moving, rocky streams
while G. holbrooki live in slow moving water with lots of green algae that
can block the light. Make a hypothesis regarding what selective pressures
could be driving the evolution of the opsin gene of these fishes.
Remember opsin is important for detection of light in the eye. [LS3(9-11)7c,8a Broad area 1.1]
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PTC Assessment-Student Version
Q10. Based on your data from the newly discovered population of
guppies, what type of environment do you think these fish might have
come from? Explain your reasoning. [Broad area 1.1, 4.12]
References
1. Olendorf et al. Frequency-Dependent Survival in Natural Guppy
Populations. Nature. Vo1 144. 1 June 2006.
2. Smith et al. Ultraviolet Vision and Mate Choice in the Guppy.
Behavioral Ecology. Vo1 13. 2002.
* Not based on real data.
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