BIOL 331: ADVANCED
DEVELOPMENTAL BIOLOGY
COMPREHENSIVE REVIEW QUESTIONS
& VERIFIED ANSWERS 2026/2027
UPDATE
1. During Drosophila development, which gene is responsible for organizing the anterior-
posterior axis and acts as a morphogen by diffusing from the anterior pole?
A. Bicoid
B. Nanos
C. Hunchback
D. Caudal
Answer: A
Conceptual Explanation: Bicoid is a maternal effect gene that forms a concentration
gradient from the anterior end, acting as a transcription factor and translation inhibitor to
specify anterior structures.
2. Which cellular process is characterized by the conversion of a group of epithelial cells into
migratory mesenchymal cells, facilitating gastrulation and neural crest migration?
A. Apoptosis
,B. Epiboly
C. Invagination
D. Epithelial-Mesenchymal Transition (EMT)
Answer: D
Conceptual Explanation: EMT involves the loss of cell-cell adhesion (like E-cadherin) and
the acquisition of migratory properties, essential for gastrulation and organogenesis.
3. In the Wnt signaling pathway, what is the fate of beta-catenin in the absence of a Wnt
ligand?
A. It translocates to the nucleus to activate transcription.
B. It binds to the Frizzled receptor to initiate signaling.
C. It is phosphorylated by a destruction complex and targeted for degradation.
D. It stabilizes the actin cytoskeleton at the cell membrane.
Answer: C
Conceptual Explanation: Without Wnt, a complex containing GSK3, Axin, and APC
phosphorylates beta-catenin, leading to its ubiquitination and degradation by the
proteasome.
4. The Spemann-Mangold organizer in amphibians induces the formation of the neural tube
by secreting inhibitors of which signaling molecule?
A. FGF
, B. Sonic Hedgehog
C. BMP4
D. Retinoic Acid
Answer: C
Conceptual Explanation: The organizer secretes Chordin, Noggin, and Follistatin, which
bind to and inhibit BMPs. Since BMPs promote ectoderm to become epidermis, their
inhibition allows the ectoderm to default to neural tissue.
5. Which phenomenon describes the observation that genes located at the 3’ end of the Hox
cluster are expressed earlier and more anteriorly than those at the 5’ end?
A. Homeotic transformation
B. Spatial and temporal collinearity
C. Alternative splicing
D. Dosage compensation
Answer: B
Conceptual Explanation: Hox genes exhibit collinearity, where their physical order on the
chromosome corresponds to their expression pattern along the body axis.
6. What is the primary role of the Zone of Polarizing Activity (ZPA) in the developing
vertebrate limb?
A. Specifying the anterior-posterior axis via Shh secretion.
DEVELOPMENTAL BIOLOGY
COMPREHENSIVE REVIEW QUESTIONS
& VERIFIED ANSWERS 2026/2027
UPDATE
1. During Drosophila development, which gene is responsible for organizing the anterior-
posterior axis and acts as a morphogen by diffusing from the anterior pole?
A. Bicoid
B. Nanos
C. Hunchback
D. Caudal
Answer: A
Conceptual Explanation: Bicoid is a maternal effect gene that forms a concentration
gradient from the anterior end, acting as a transcription factor and translation inhibitor to
specify anterior structures.
2. Which cellular process is characterized by the conversion of a group of epithelial cells into
migratory mesenchymal cells, facilitating gastrulation and neural crest migration?
A. Apoptosis
,B. Epiboly
C. Invagination
D. Epithelial-Mesenchymal Transition (EMT)
Answer: D
Conceptual Explanation: EMT involves the loss of cell-cell adhesion (like E-cadherin) and
the acquisition of migratory properties, essential for gastrulation and organogenesis.
3. In the Wnt signaling pathway, what is the fate of beta-catenin in the absence of a Wnt
ligand?
A. It translocates to the nucleus to activate transcription.
B. It binds to the Frizzled receptor to initiate signaling.
C. It is phosphorylated by a destruction complex and targeted for degradation.
D. It stabilizes the actin cytoskeleton at the cell membrane.
Answer: C
Conceptual Explanation: Without Wnt, a complex containing GSK3, Axin, and APC
phosphorylates beta-catenin, leading to its ubiquitination and degradation by the
proteasome.
4. The Spemann-Mangold organizer in amphibians induces the formation of the neural tube
by secreting inhibitors of which signaling molecule?
A. FGF
, B. Sonic Hedgehog
C. BMP4
D. Retinoic Acid
Answer: C
Conceptual Explanation: The organizer secretes Chordin, Noggin, and Follistatin, which
bind to and inhibit BMPs. Since BMPs promote ectoderm to become epidermis, their
inhibition allows the ectoderm to default to neural tissue.
5. Which phenomenon describes the observation that genes located at the 3’ end of the Hox
cluster are expressed earlier and more anteriorly than those at the 5’ end?
A. Homeotic transformation
B. Spatial and temporal collinearity
C. Alternative splicing
D. Dosage compensation
Answer: B
Conceptual Explanation: Hox genes exhibit collinearity, where their physical order on the
chromosome corresponds to their expression pattern along the body axis.
6. What is the primary role of the Zone of Polarizing Activity (ZPA) in the developing
vertebrate limb?
A. Specifying the anterior-posterior axis via Shh secretion.
