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Biology 411 - Developmental Biology
Winter Quarter 2007
Midterm 1
100 Total Points
Open Book
25 questions - 4 pts each
(3 pts Extra Credit on last page)
Provide answers using full sentences, unless instructed otherwise.
Chapter 8
1.
Label the following structures in the late sea urchin gastrula.
1. blastopore
2. archenteron roof
(endoderm acceptable)
3. secondary mesenchyme
4. primary mesenchyme
5. ectoderm
2. Draw a diagram of an early cleavage sea urchin embryo, immediately after the 5th cell
cleavage (p. 217-219). Identify which regions of this embryo are fated to become the structures
you have labeled in Question 1.
refer to diagram in text
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3. Explain why removal of the polar lobe after 1st cell division in molluscan embryos results in
the loss of spiral cleavage (p. 234)
Polar lobe material is normally absorbed into the D blastomere. Polar lobe material
contains determinants for the cleavage orientation of the D blastomere, which is necessary
for the orientation of the 4d blastomere. The position of the 4d blastomere determines the
coiling pattern of the developing snail.
4.
What would occur if P-granules were removed from a C. elegans embryo (p. 246)?
Removal of P-granules would result in a lack of germ line cell specification.
5. Describe the phenotype of progeny from a female snail that is hemizygous for the dextral
gene (i.e. D/-). (p. 232)
All progeny would have normal right-handed coiling pattern. A single copy of the D allele
is sufficient to maintain the wild-type maternal effect phenotype.
6. How does maternal nuclear beta-catenin activate skeletogenic genes in sea urchins.
(p. 221).
Maternal beta-catenin in the nucleus bind to the promotor of the Pmar1 gene. Pmar1
represses a repressor of Tbr and Ets. Tbr and Ets activate the expression of skeletogenic
differentiation genes.
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Name ___________________________________________
Chapter 9
7. In the Drosophila blastoderm, explain why engrailed is not expressed in cells expressing
wingless (p. 282).
engrailed expression is activated in cells with elevated eve or ftz. wingless is expressed in
cells that express neither eve or ftz.
8. What effect would microtubule disassembly have the localization of maternal determinates
in Drosophila, if the microtubule disassembly occurred during oogenesis (p. 260)?
Loss of microtubules would disrupt the localization of bicoid, gurken, and nanos.
Anterior-posterior, dorsal-ventral, and pole cell specification would be disrupted,
respectively, as a downstream consequence of these mis-localization of bicoid, gurken, and
nanos.
9.
Draw the pattern of "active" Torso protein in a torso-like mutant Drosophila oocyte (p. 274).
There is no activation of Torso anywhere.
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10. Describe how the Dorsal protein interacts with the gene products of zerknullt (zen) and
decapentaplegic (dpp) to establish dorsal-ventral polarity in the Drosophila blastoderm (p. 265).
Dorsal inhibits the expression of zen and dpp, thus promoting ventral fates in the
Drosophila blastoderm.
11. What possible purpose does parasegment specification have in arthropod development
(p. 276)?
Parasegment construction of the arthropod body plan allows adjacent segments to be
innervated by a single ganglion. This allows for synchronized muscular contraction in
adjacent body segments.
12. What two tiers of the genetic hierarchy in Drosophila early development contain genes
that are activators of Hox genes (p. 267)?
Both pair-rule and segment polarity genes can activate Hox genes.
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Name ___________________________________________
Chapter 10
13. Explain how the location of the Nieuwkoop Center is established in the frog embryo before
the first cleavage (p. 310).
Disheveled protein and GBP (Glycogen Synthease Kinase-3 Binding Protein) are
transported along microtubules by kinesin to the dorso-vegetal region of the frog embryo
during the end of the first cell cycle. Disheveled and GBP act to inhibit the activity of
GSK-3 (Glycogen Synthease Kinase-3). Loss of phosphorylation of beta-catenin results in
the stabilization of beta-catenin. As the embryo cleaves, stabilized beta-catenin becomes
localized in the dorso-vegetal blastomeres of the embryo, thus establishing the locus of the
embryo's Nieuwkoop Center.
14. Explain the molecular events in the Nieuwkoop Center, after it becomes active following
the midblastula transition (p. 311).
Inhibition of beta-catenin phosphorylation results in decrease of beta-catenin degradation.
Beta-catenin can then translocate to the nucleus and bind to the Tcf3/LEF transcription
factor, leading to the expression of siamois. Siamois expression demarcates the locus of the
Nieuwkoop Center. Siamois helps activate goosecoid, a gene that is partially responsible
for the functions of the Spemann-Mangold Organizer.
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15. What are the names of two signaling pathways that are involved in the specification of the
Spemann-Mangold Organizer (p. 312)?
Wnt, as well as Nodal and BMP (bothTGF-beta signaling pathways) signaling events are
involved in the specification of the Spemann-Mangold Organizer.
16. What does the embryological term "determined" mean?
Detemination means that a restriction in cell fate can no longer be altered by inductive
signals. If the cell is transplanted to an ectopic location, the cell and its progeny will
continue to differentiate according to their cell fate specification obtained at their site of
origin.
17. In molecular terms, explain why different portions of dorsal mesendoderm (i.e. roof of the
archenteron) induce neural plate to form different neural structures (pp. 318-319).
Different regions of the dorsal mesendoderm secrete different combinations of BMP and
Wnt pathway antagonists. Depending on the local combination of antagonists, the
ectoderm is induced to form brain, spinal cord, or epidermis.
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Name ___________________________________________
18. Draw the structure of the dorsal lip of the amphibian blastoderm toward the end of
gastrulation. Clearly label the tissue layers, blastopore, and archenteron (p. 299 [remember:
Figure 10.2 is improperly colorized], p. 322).
refer to diagrams in text. One point was removed if the roof the archenteron was not
labeled as endoderm.
Chapter 11
19.
What is the embryonic shield in a fish embryo homologous to in the amphibian embryo?
The embryonic shield is homologous to the Spemann-Mangold Organizer.
20. What structure is the primitive streak in chick embryos homologous to in amphibian
embryos?
The primitive streak in chick embryos is homologous to the blastoporal lip of amphibian
embryos.
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21.
What is the purpose of a F2 mutagenesis screen (p. 327)?
The purpose of a F2 mutagenesis screen is to identify recessive mutations that affect
embryonic development. The F2 screen is designed to identify F2 parents that are
homozygous in the mutant allele.
22. What is the name of the chick organizer?
structure during gastrulation (p. 342).
Describe the morphogenetic movements of this
Hensen's node is the name of the chick organizer. It is the posterior limit of the
chordamesoderm (i.e. notochordal rudiment). During gastrulation, Hensen's moves
posteriorly as the primitive streak regresses.
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Name ___________________________________________
23. Some humans have two genetically different cell types (XY and XX) within the same body.
Provide a simple explanation for this phenomenon (p. 357).
Two fraternal twins fused during their early development. One twin was female (XX), the
other twin was male (XY).
24.
What is the fate of outer cell mass cells (p. 352)?
The fate of the outer cell mass is to form a major portion of the chorion. The chorion is
composed of a cytotrophoblast and a syncytiotrophoblast, derived from the outer mass
cells.
25. Explain how Kupffer's vesicle is thought to participate in the establishment of left-right
asymmetry in the zebrafish embryo (p. 336).
Monocilia in the epithelial cells of Kupffer's vesicle create a counterclockwise movement of
fluid within the vesicle. It is thought that morphogens are redistributed as a result of this
fluid flow, resulting in the differential activation of intracellular calcium and target genes
on the left side of tailbud.
Extra Credit (3 pts)
26. In amphibians, what role does the blastocoel play in the specification of germ layers?
(p. 307).
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The blastocoel separates the animal pole from the vegetal prospective endoderm.
Mesoderm inducing signals are not well transmitted through the blastocoel fluid, thus
preventing the animal cap from being induced to become mesoderm.
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