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Biology 4361
Exam 3
July 21, 2008
Name:______KEY__________
ID#: ____________________
Multiple choice (one point each; indicate the best answer)
1. The cell cycle is directed by mitosis-promoting factor, which consists of
a. microtubules and microfilaments.
b. dynein and kinesin.
c. F and G actin.
d. cyclin B and cdc2.
2. During sea urchin gastrulation, the eventual mouth area of ectoderm is specified by the
presence of
a. Nodal.
b. Shh.
c. Wnt8.
d. BMP2.
3. At the 64-cell stage, sea urchin blastomeres
a. are uncommitted.
b. are uncommitted, except for the micromeres.
c. are specified, but not determined.
d. are partially specified.
4. The sea urchin blastocoel
a. is created by osmotic pressure.
b. requires epithelial cells connected by tight junctions.
c. fills with proteinaceous fluids
d. all of the above.
5. In the sea urchin, the 4th cleavage is unequal, producing _____________ in the vegetal region.
a. macromeres and micromeres.
b. mesomeres.
c. macromeres, mesomeres, and micromeres.
d. none of the above.
6. Yolk distribution in eggs from which two taxa is similar?
a. echinoderm, amphibian
b. insect, amphibian
c. amphibian, mammal
d. sea urchin, mammal
7. Cytokinesis is driven by
a. microfilaments.
b. microtubules.
c. microfilaments and microtubules.
d. microfilaments, microtubules, and kinesin.
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8. During gastrulation, cell movement in which one cellular sheet splits into two layers is called
a. invagination.
b. involution.
c. ingression.
d. delamination.
9. Drosophila eggs are described as
a. isolecithal.
b. mesolecithal.
c. telolecithal.
d. centrolecithal.
10. In Drosophila, eggs are activated
a. prior to fertilization.
b. by sperm binding.
c. by pronuclear fusion.
d. after the first nuclear division.
11. During Drosophila egg formation the presence of the gurken protein posteriorizes the
a. egg nucleus.
b. adjacent nurse cells.
c. adjacent follicular cells.
d. all of the above.
12. Which motor protein moves towards the growing (+) end of microtubules?
a. axin
b. myosin
c. kinesin
d. dynein
13. During Drosophila egg formation, bicoid messages associate with
a. dynein.
b. the capped end of microtubules.
c. the anterior pole.
d. all of the above.
14. Drosophila acron and telson regions are specified by which genes?
a. bicoid and nanos
b. gurken and torpedo
c. toll and pipe
d. torso and torso-like
15. In deuterostomes, the blastopore becomes the
a. mouth.
b. pharynx.
c. gut.
d. anus.
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16. The cells on the leading edge of migration inside the amphibian gastrula are composed of
a. pharyngeal endoderm.
b. chordamesoderm
c. head mesoderm.
d. vegetal endoderm.
17. In amphibian embryos, involution occurs at the
a. dorsal lip of the blastopore.
b. dorsal and lateral lips of the blastopore.
c. dorsal, lateral, and ventral lips of the blastopore.
d. dorsal, lateral, ventral, and central lips of the blastopore.
18. Which of the following cell movements are not active during amphibian gastrulation?
a. intercalation
b. epiboly
c. involution
d. all of the above are active
19. Which of the following genes are associated with specification of the dorsal lip of the
blastopore of amphibian embryos.
a. sonic hedgehog
b. siamois
c. ultrabithorax
d. none of the above
20. Amphibian Vg1
a. is a transcription factor.
b. specifies endoderm.
c. specifies mesoderm.
d. both a. and c.
21. Areas of the amphibian embryo that are high in β-catenin, Vg1, and Nodal will likely form
a. endoderm.
b. organizer.
c. ventral mesoderm.
d. none of the above
22. In birds, the _________________ forms the embryo proper.
a. primary hypoblast.
b. secondary hypoblast.
c. epiblast.
d. none of the above.
23. In birds, the blastocoel is formed in the space between
a. the primary and secondary hypoblasts.
b. the area pellucida and area opaca.
c. Koller’s sickle and the posterior marginal zone.
d. the epiblast and hypoblast.
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24. Which are equivalent?
a. dorsal lip of the blastopore; Hensen’s node
b. Koller’s sickle; blastopore
c. blastocoel; blastodisc
d. none of the above
25. In vertebrate embryos the hypoblast
a. is made of mesoderm.
b. is replaced by endoderm.
c. joins the ectoderm to form neurectoderm.
d. is the first structure formed by ingressing mesenchymal cells.
26. The mammalian zona pellucida
a. protects the cleavage-stage embryo.
b. prevents adhesion of the embryo to the fallopian tube.
c. contains the embryo until the blastocyst stage.
d. all of the above.
27. The syncytiotrophoblast
a. lines the uterine blood vessels.
b. creates the amnion.
c. creates the yolk sac.
d. digests the endometrium tissue to create openings.
28. Wnts, BMPs, FGFs, and retinoic acid are all associated with ____________ specification.
a. anterior
b. posterior
c. dorsal
d. ventral
29. In vertebrates, Hox genes
a. are expressed in a 3’to 5’ manner.
b. exist in multiple copies.
c. have homologues in Drosophila.
d. all of the above.
30. In mammalian embryogenesis, the left-right axis is determined by
a. activation of Nodal on the left side of the primitive streak.
b. suppression of dynein ATPase.
c. activation of FGF on the left side of the primitive streak.
d. the absence of calcium ions.
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True / False (1 point each)
31. Cells with degraded cyclin B will not undergo division. True / False
32. During sea urchin cleavage, micromeres are specified by β-catenin. True / False
33. In general, telolecithal eggs undergo holoblastic cleavage. True / False
34. During cleavage, the spindles are always located in the center of the cell. True / False
35. In Drosophila eggs, the protein Gurken binds to the Torpedo receptor. True / False
36. In Drosophila embryos, the pole cells eventually form the acron and telson. True / False
37. In amphibian embryos, mesoderm is induced by ectoderm. True / False
38. Cavitation in mammalian embryos is induced by the trophoblast. True / False
39. The bilaminar germ disc is made up of the trophoblast and the inner cell mass. True / False
40. In chicks, gastrulating cells convert from epithelium to mesenchyme. True / False
Fill in. 41 – 50 (1 point each)
aortic arch
atrium
olfactory placode
optic cup
otic vesicle
aortic arch
pharyngeal pouch
atrium
somite
otic vesicle
pharyngeal pouch
somite
spinal cord
telencephalon
vitelline vein
optic cup
telencephalon
olfactory placode
spinal cord
vitelline vein
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Define. Write a brief definition of any five of the terms or phrases (2 points each):
51. Bilaminar germ disc
The epiblast and hypoblast of the mammalian blastocyst.
52. Compaction
The compression of blastomeres in the 8-cell stage of mammalian cleavage-stage embryos;
accompanied by formation of tight junctions and the formation of inner and outer cells.
53. Convergent extension
A process of cell/tissue movement which involves the intercalation of adjacent cells such that
several layers (or rows, in epithelial sheets) join to form fewer layers (or rows), reducing the
width, and concomitantly increasing the length of the tissue.
54. Gene expression hierarchy
A process by which one gene (or set or family) of genes stimulates the expression of a second set
(or family), which stimulates a third, etc.
55. Involuting marginal zone
The area of ectoderm in a gastrulating amphibian embryo that moves across the blastopore lip
and into the embryo.
56. Mid-blastula transition
The point (or process) during which control over development switches from maternal (i.e. in the
form of stored regulatory components) to embryonic (i.e. transcriptionally-derived) control.
57. Mitosis promoting factor
The combination of cdc2 (a cyclin-dependent protein kinase) and its activator, cyclin B.
58. Ventral furrow
The area in the ventral-most aspect of the Drosophila early gastrula where mesoderm
enters the embryo.
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Short Answer. Answer any four (5 points each). Be certain to address all parts of
the questions.
59. Describe cell cycle regulation in both cleavage-stage and post-cleavage-stage cells.
Mitosis is stimulated by MPF (mitosis promoting factor), which consists of cdc2 (cyclindependent kinase) and its activator, cyclin B. Active MPF phosphorylates nuclear components
that are necessary to initiate mitosis. Cyclin B degrades quickly, inactivating cdc2. This
degradation limits mitotic events, which do not resume until cyclin B has been resupplied.
In cleavage-stage embryos, cyclin B mRNA is supplied in maternally-derived stores; therefore,
the cell cycle can continue without G phases, whereas post-cleavage-stage embryos institute G
phases to transcribe new cyclin B transcripts (among other nuclear components).
60. In Drosophila, mesoderm, neurectoderm, and lateral ectoderm specification depends on the
activation of genes by the Dorsal transcription factor. Explain this phenomenon in terms of a
Dorsal concentration gradient.
The transcription factor Dorsal is produced in the ventral-most region of the Drosophila embryo,
and diffuses dorsally, forming a concentration gradient. Genes specifying mesoderm contain
weak enhancer elements, which will be activated only at the highest Dorsal concentrations.
Genes specifying neurectoderm and lateral ectoderm have stronger enhancers, and will be
activated at progressively lower Dorsal concentrations, which are found in more dorsal areas of
the concentration gradient.
60. A) Place the following Drosophila gene groups in the proper order of expression.
B) What is the overall effect of the hierarchical expression of these genes in Drosophila
development?
gap, homeotic selector, maternal effect, pair rule, segment polarity
Maternal effect, gap, pair rule, segment polarity, homeotic selector
Gene products (paracrine or transcription factors) or combinations of gene products from
preceding expressions activate the expression of subsequent sets. In Drosophila, these successive
sets of gene expression create finer patterns of segmentation, starting first with polarization
genes (e.g. maternal effect genes bicoid and nanos), proceeding through specifying large regions
(gap genes), then smaller segments and parasegments. Finally, segmental identity is established
by the combination homeotic selector genes, which are differentially stimulated by the preceding
gene products.
60. A) List three types of cell movements that take place during amphibian gastrulation.
B) For each type, describe where and when during the process that it takes place.
Involution – involuting marginal zone (ectoderm) at the dorsal lip of the blastopore throughout
gastrulation
Invagination – dorsal lip of the blastopore at the start of gastrulation (bottle cells)
Epiboly – involuting marginal zone and ectoderm) throughout gastrulation
Convergent extension – ectoderm, throughout gastrulation
Migration – pharyngeal endoderm, etc (including various mesoderms), during involution
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62. A) What is the general function of Hox genes in mammalian embryogenesis?
B) Describe the effects one would expect in a Hox knockout organism.
Hox genes specify the identity of various tissues and organs along a particular axis; e.g.
determination of brain regions, vertebral structures, and limb segments.
Hox knockouts (complete; i.e. all functioning paralogues eliminated) generally result in respecification of the segment or structure towards a fate determined by the next 3’-Hox
expression. For example, if all paralogues of Hox6 were eliminated, the segment specified by
Hox6 would take on the identity of Hox5.
64. For each of the following cells, tissues, or structures;
A) List a homologous cell, etc. from another model species (specify which model used).
B) Describe what characteristics are homologous.
1. Sea urchin micromeres
- amphibian dorsal lip of the blastopore
- chick Hensen’s node
- mammalian node
Each are self-specified and direct the specification of all other tissues.s
2. Mammalian blastocyst
- amphibian, echinoderm blastula
- fish, chick blastodisc
Each provides the structure for gastrulation to take place.
3. Chick primitive streak
- amphibian blastopore (or dorsal lip of the blastopore)
- echinoderm vegetal plate
- mammalian primitive streak (or node)
Each is the structure through which cells move into the embryo during gastrulation.
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Short Essay. Answer any two(10 points each). Be certain to address all parts of the
questions and provide complete answers.
65. Describe how Gurken acts to establish dorsal and ventral fates in Drosophila embryos.
Gurken is expressed only along the dorsal margin of the egg (following the path of the nucleus)
(Note – the Gurken protein does not diffuse far; therefore, the effect of the protein is limited to
the dorsal region, close to where it is initially expressed.)
Gurken binds to its receptor, Torpedo, which acts to inhibit the production of the protein Pipe in
the dorsal follicular cells.
Since Gurken is not present in the ventral region, Pipe is expressed in the ventral follicles.
Pipe interacts with the egg protein Nudel, which initiates series of proteolytic cleavages of
factors in the perivitelline space that eventually results in activated Spatzle.
Spatzle activates egg Toll receptors.
Toll binding leads to the activation of the transcription factor Dorsal, by dissociating it from the
inhibitory Cactus protein.
Active Dorsal moves into syncitial blastoderm nuclei to initiate ventralizing (mesoderm
-specifying) gene expression.
66. Describe how the dorsal lip of the blastopore is specified in amphibian embryos.
The dorsal lip of the blastopore is specified by a combination of β-catenin, VegT, Vg1, and nodalrelated (Xnr) genes. VegT, Vg1, and Xnr genes are produced in relatively high concentration by
the vegetal region. β-catenin is ubiquitous throughout the embryo, but is degraded everywhere
but the future dorsal lip area. (NOTE – answers describing initiation by β-catenin in detail will
be accepted).
Cortical rotation and kinesin activity moves the protein Dishevelled into the future dorsal lip
area.
- vegetal cortex Dsh is attached to GBP and kinesin
- kinesin moves the complex toward the marginal zone
- cortical rotation moves the entire region towards the marginal zone
Once in the marginal zone, Dishevelled blocks the activity of GSK3, which otherwise participates
in β-catenin degradation.
β-catenin acts as a transcription factor along with Tcf3, stimulating dorsal lip specifying genes
such as siamois and goosecoid.
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67. Describe the specification of Drosophila anterior and posterior regions with respect to the
location, expression, and effect of bicoid and nanos genes.
The mRNA for bicoid and nanos are produced by the nurse cells and moved into the oocyte.
Bicoid messages associate with dynein at the capped (-) end of microtubules, which are polarized
(with their capped (-) ends anterior, growing (+) ends posterior).
Nanos messages associate with the Oskar protein, which is associated with the growing (+) ends
of the microtubules at the posterior end of the egg.
Expression of the bicoid and nanos genes in the anterior and posterior regions, respectively,
results in formation of opposing protein gradients.
Bicoid protein acts as a transcription factor, inducing the expression of Hunchback, which
specifies anterior fates. Bicoid protein also inhibits the translation of nanos genes, which
limits nanos expression to areas lacking Bicoid.
Nanos protein acts as a transcription factor, inducing the expression of Caudal, which specifies
posterior fates. Nanos protein also inhibits the translation of bicoid genes, which limits bicoid
expression to areas lacking Nanos.
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