Biology
Name / pledge:
1. In Drosophila, mRNA of the maternal effect gene gurken is localized in the dorsal region of eggs, while a second
protein-coding gene, pipe, is normally expressed only on the ventral surface of eggs. Eggs with wild-type expression
of gurken and pipe eventually develop normal dorsal and ventral em
yonic structures in the appropriate places.
However, female flies homozygous for a gurken null mutation lay eggs that lack functional gurken mRNA, and the
egion of pipe expression expands to include the surface of the entire egg. Such em
yos are unable to
develop dorsal structures, and ventral structures develop on both sides of the early em
yo. (See image at right,
which shows cross-sections of eggs and early em
yos of both wild-type and mutant flies.)
A. What does the information above suggest about the normal regulatory relationship between gurken and pipe?
Briefly explain (2 points).
B. What does the information above suggest about the normal roles of gurken and pipe in the development of
dorsal and ventral structures? Briefly explain (2 points).
C. Imagine that you are able to isolate gurken mRNA. How could you use this mRNA to experimentally test the
egulatory hypothesis you proposed in (A)? Briefly explain your proposed experimental test (2 points).
D. Three other protein-coding genes downstream of gurken are also involved in controlling pipe expression:
capicua, mi
or, and torpedo. Here is information about the phenotypic effects of mutations in these genes:
● Mutants lacking capicua, no pipe expression
● Mutants lacking mi
or, expanded pipe expression
● Mutants lacking torpedo, expanded pipe expression
● Double mutants lacking both capicua and mi
or, expanded pipe expression
● Double mutants lacking both capicua and torpedo, no pipe expression
Using the a
ow and T-bar system (you may copy and paste the → and⟞ symbols as needed), complete the
developmental regulatory pathway that controls the expression of pipe in the space below (6 points).
E. The protein products of capicua and mi
or are both transcription factors; now propose a hypothesis that is
consistent with the developmental pathway you proposed in (D) that would explain how capicua and mi
o
could modify pipe expression by acting as transcription factors, and
iefly explain your hypothesis (3 points).
2. You have identified a DNA cis-regulatory element (CRE, or enhancer) that is responsible for the expression of
the Drosophila gene even-skipped in stripes 3 and 7, as it can switch on expression of a reporter gene (blue) in
those stripe regions (panel A). You next decide to test this CRE in various mutant em
yos, and observe reporte
gene expression in each of those em
yos.
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A. You begin with a tailless mutant em
yo (Panel D). Based on the observed pattern of expression, what do you
conclude is the normal role of tailless in regulating this CRE, and why do you conclude that (2 points)?
B. You next observe reporter gene expression in a knirps mutant (Panel B). Based on the observed pattern of
expression, what is the normal role of knirps in regulating this CRE, and why do you conclude that (2 points)?
C. Finally, you observe expression in a mutant lacking both knirps and torpedo (Panel E). Based on the observed
pattern of expression, what is the normal role of torpedo in regulating the CRE, and why do you conclude that (2
points)?
3. During development in verte
ates, mesodermal cells near the neural tube
ecome organized into blocks of tissue called somites. Initially the cells that
comprise the somites are undifferentiated and appear identical to each other.
Later in development, however, the cells begin to differentiate and become eithe
connective tissue, muscle, or bone (see diagram of somite at right). Describe an
experiment you could use to decide whether cell fate in the somites is
determined or undetermined at the early stage of somite development when all
cells appear identical. Briefly explain your expected outcomes and how you
would interpret them (4 points).
Exam continues on next page
4. During the early stages of
mouse lung formation, cells in
the lung epithelium (a layer of
endodermal cells) divide and
form primary (1o)
onchial
tubules which then
anch and
form additional secondary (2o)
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and tertiary (3o) tubules. The epithelial cells overlie, but are not in direct contact with, a different cell type, the lung
mesenchyme. If the lung mesenchyme is either removed or replaced with kidney mesenchyme, the cells of the
epithelium do not divide, and
onchial tubules do not form.
A. Why do the results described above indicate induction via a diffusible signal? Briefly explain, and include in
your explanation a
ief definition of induction (2 points).
B. Further study shows that lung mesenchyme cells secrete two diffusible signal molecules that kidney mesenchyme
cells do not: Fi
oblast Growth Factor (FGF) and Bone Morphogenic Protein (BMP). Using what you have
learned about how experiments with FGF have clarified its role in the development of verte
ate limbs, describe how
you could experimentally and conclusively determine whether just one or both of these signal molecules are
equired to induce
onchial tube formation in the lung epithelium. Briefly explain your proposed experimental
procedure, and
iefly explain how it would allow you to make this determination (3 points).
C. Suppose that after performing the experiment you designed in (B), you acquire conclusive evidence that FGF, and
not BMP, is the diffusible signal molecule involved in
onchial tubule formation. FGF performs its role as a signal
molecule by binding with a receptor kinase. Where would you expect to find FGF receptors in the lung cells
described above, and what is likely to be the end result of FGF binding with the receptor? Be sure to include in you
answer the cell type where you would expect to find the FGF receptor, its expected subcellular location within
the cell, and how FGF binding with the receptor might lead to altered lung development (3 points).
D. Altered FGF signaling has also been implicated in certain types of lung cancers; would you expect FGF to be
underexpressed or overexpressed in cells that are part of lung cancer tumors? Briefly explain (2 points).
E. Min et al. (1998, Genes and Development 12: XXXXXXXXXXgenerated mutant FGF-deficient mice in which the gene
for FGF had been deleted. What predictions can you make about both lung development and limb development
in these FGF-deficient mice? Briefly explain (2 points).
F. Compare and contrast the role of FGF in lung development and limb development, and include in your answer an
explanation of how two different tissues – developing lungs and developing limbs – can respond very
differently to the same signal molecule (3 points).
Exam continues on next page5. Despite its name, the protein Yellow is required to produce dark body pigment in
Drosophila. In most species of fruit flies, like D. willistoni (right) Yellow protein (and dark pigmentation) is expressed
only in the posterior margins of the six
abdominal segments. In D. melanogaster and
D. biarmipes, however, the region of Yellow
expression is expanded; Yellow protein and
dark pigmentation is present throughout the last
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two abdominal segments (segments A5 and A6), an expression pattern that co
esponds to expression of the
transcription factor Abd-B. Similarly, in D. biarmipes, the region of Yellow expression has expanded to include the
distal part of the wing, an expression pattern that co
esponds to expression of the transcription factor Distal-less.
Based on this information and what you have learned about the evolutionary loss of pelvic spines in freshwate
sticklebacks, propose a hypothesis that would explain how the expression of Yellow protein has become expanded
in melanogaster and biarmipes,
iefly explain your hypothesis, and
iefly contrast your hypothesis to what
you know about the loss of pelvic spines in freshwater sticklebacks (5 points).
6. Expression of shh (sonic hedgehog) in the ZPA (zone of polarizing activity) of
verte
ate limb buds is controlled by the ZRS (ZPA Regulatory Sequence), a
cis-regulatory element (CRE or enhancer) upstream of the shh coding region
(see figure at right). The table below summarizes the results of experiments on
mice in which the ZRS of mice is replaced with the ZRS of another organism:
ZRS of mouse replaced with ZRS of: shh expression in mouse limb bud Mouse limb development
Coelacanth (lobe-finned fish) Normal Normal
Human Normal Normal
Python (snake that forms rudimentary limb buds) Weakened Partial limb truncation
Co
a (snake that does not form limb buds at all) None Severe limb truncation
A. What do these findings suggest about the evolutionary developmental basis of limb loss in snakes, and
how do these findings relate to what is known about the evolutionary loss of pelvic spines in freshwate
sticklebacks? Briefly explain (2 points).
B. The ZRS of mice includes multiple binding sites for at least five different transcription factors (HAND2,
ETS1, HOXD9, HOXD10, and HOXD13) and is activated when bound to these transcription factors. Based on
this observation and the findings presented in the table above, what prediction could you make about the ZRS of
pythons compared to the ZRS of mice and the ZRS of co
as? Briefly explain (3 points).