Developmental Biology TEST

1.

In Drosophila imaginal disc development, Wingless (Wg) and Decapentaplegic (Dpp) act as orthogonal morphogen gradients. Cells at their intersection express Distalless gene. What does this spatial expression signify?

A. Distalless is expressed where Wg or Dpp alone is high.
B. Distalless expression requires combined signaling thresholds of both Wg and Dpp.
C. Distalless is repressed by both Wg and Dpp.
D. Distalless expression is random within imaginal discs.

2.

In limb regeneration of salamanders, removal of nerve supply prevents regeneration. Implantation of beads soaked in FGF2 partially rescues the process. This indicates:

A. FGF2 alone is sufficient for complete regeneration.
B. Nerve supply provides trophic factors like FGFs essential for blastema maintenance.
C. Regeneration depends only on dedifferentiation.
D. FGF2 inhibits wound healing.

3.

A planarian is bisected transversely into anterior and posterior halves. Both regenerate complete organisms, but inhibition of β-catenin results in double-headed worms. What does this suggest?

A. β-catenin promotes anterior identity.
B. β-catenin specifies posterior identity.
C. β-catenin induces apoptosis in posterior cells.
D. β-catenin is irrelevant to polarity.

4.

In amphibians, removal of notochord during neurulation results in the absence of the floor plate and motor neurons in the neural tube. Which molecule is responsible for this inductive effect?

A. BMP4
B. Sonic Hedgehog (SHH)
C. Retinoic acid
D. FGF8

5.

During chick eye development, removal of the optic vesicle before lens induction prevents lens formation. However, if optic vesicle tissue is grafted back later, lens induction still fails. What does this indicate?

A. Optic vesicle continuously maintains lens development.
B. Lens induction requires early contact between optic vesicle and ectoderm during a specific competence window.
C. Ectoderm can form lens at any stage after optic vesicle contact.
D. Lens induction is independent of optic vesicle signaling.

6.

In an amphibian embryo, UV irradiation of the vegetal pole before fertilization leads to embryos without dorsal structures. Injection of β-catenin mRNA rescues the normal dorsal development. What does this imply?

A. β-catenin acts upstream of cortical rotation.
B. β-catenin is a key dorsal determinant activated by cortical rotation.
C. UV light directly inactivates β-catenin.
D. Dorsal determinants are nuclear transcription factors.

7.

Removal of the apical ectodermal ridge (AER) from a developing chick limb bud results in limb truncation. However, if FGF8-soaked beads are implanted, limb development continues normally. What does this show?

A. FGF8 promotes limb outgrowth by maintaining progress zone proliferation.
B. FGF8 controls digit identity.
C. FGF8 represses SHH expression.
D. FGF8 induces apoptosis in AER.

8.

In a Drosophila embryo, a gap gene mutation causes the loss of consecutive body segments. Which gene class acts downstream to refine and subdivide these segments into specific patterns?

A. Maternal effect genes
B. Pair-rule genes
C. Segment polarity genes
D. Homeotic genes

9.

In C. elegans, if EMS cell is isolated and cultured without P2 cell, it divides into two endodermal cells. When cultured with P2, one cell forms mesoderm and one endoderm. What conclusion can be drawn?

A. P2 provides inhibitory signal to EMS.
B. P2 induces mesoderm formation via cell-cell signaling.
C. EMS is autonomously specified.
D. P2 prevents endoderm formation.

10.

When a chick embryo is exposed to exogenous retinoic acid during neurulation, multiple limb buds form in abnormal positions. Which statement best explains this effect?

A. Retinoic acid represses SHH signaling.
B. Retinoic acid alters Hox gene expression pattern, shifting positional identity.
C. RA promotes random proliferation of mesoderm.
D. RA inhibits FGF8 signaling at the AER.

11.

In mouse embryos, Hox genes show colinearity: their order on chromosome corresponds to their spatial expression. If Hoxb8 is experimentally expressed in anterior neural tissue, what happens?

A. No change occurs due to positional resistance.
B. Posteriorization of anterior structures occurs.
C. Duplication of anterior neural tissue occurs.
D. Loss of neural crest formation occurs.

12.

An experiment on zebrafish shows that inhibition of Nodal signaling leads to absence of mesoderm and endoderm, but ectoderm remains normal. What does this indicate about Nodal’s developmental role?

A. Nodal is essential for neural induction.
B. Nodal specifies mesendodermal lineages.
C. Nodal acts only during gastrulation.
D. Nodal promotes anterior development.

13.

In Drosophila, loss-of-function of torpedo gene (EGF receptor) in follicle cells leads to ventralized embryos. However, injecting gurken mRNA into oocytes rescues the phenotype partially. What does this reveal?

A. Torpedo acts downstream of gurken.
B. Gurken and torpedo act in the same pathway but in different cells.
C. Gurken is independent of torpedo for dorsal signaling.
D. Torpedo and gurken act in parallel redundant pathways.

14.

A researcher overexpresses BMP4 uniformly in a Xenopus embryo. Despite this, a small patch of neural tissue forms near the dorsal side. Which mechanism best explains this observation?

A. Local suppression of BMP4 by organizer-derived inhibitors like Chordin and Noggin.
B. BMP4 cannot act on dorsal cells due to receptor absence.
C. BMP4 degradation occurs faster in the dorsal side.
D. Dorsal side cells are committed to neural fate before BMP signaling.

15.

In Xenopus embryos, the dorsal lip of the blastopore is transplanted into the ventral region of another gastrula. The host embryo forms a secondary axis, but both axes share a common notochord.
What does this suggest about the nature of the organizer and its signaling?

A. Organizer is purely autonomous and does not require host interaction.
B. Organizer induces only neural tissues but not mesodermal differentiation.
C. Organizer induces secondary axis using both self-derived and host-derived cells.
D. Organizer acts only on vegetal hemisphere cells.

16. Apoptosis during interdigital cell death (digit separation) is regulated mainly by:
A. Wnt signaling
B. BMP signaling
C. SHH signaling
D. FGF signaling

17. During oogenesis in Drosophila, localization of gurken mRNA defines:
A. Dorsal-ventral polarity
B. Anterior-posterior polarity
C. Both A-P and D-V axes
D. Axis inversion

18. In mouse embryos, implantation occurs when the embryo reaches the:
A. Morula stage
B. Early blastocyst stage
C. Late gastrula stage
D. Neurula stage

19. In zebrafish, mutation in no tail (ntl) gene affects:
A. Eye formation
B. Notochord development
C. Heart looping
D. Brain segmentation

20. Which experiment proved that cell fate in early amphibian embryos is not fixed but regulative?
A. Spemann’s constriction experiment
B. Mangold’s graft experiment
C. Driesch’s sea urchin isolation experiment
D. Vogt’s fate mapping

21. If β-catenin is degraded in early Xenopus embryo, what occurs?
A. Extra neural tissue
B. Ventralized embryo
C. Dorsal duplication
D. Arrest of cleavage

22. In Drosophila, maternal effect genes establish:
A. Segment polarity
B. Gap gene expression
C. Anterior-posterior polarity
D. Homeotic gene regulation

23. Neural crest cells do NOT contribute to:
A. Peripheral nervous system
B. Adrenal medulla
C. Melanocytes
D. Skeletal muscle fibers

24. Inhibition of SHH signaling during limb bud development leads to:
A. Duplication of digits
B. Loss of posterior digits
C. Shortened limb
D. Formation of ectopic limbs

25. Transplanting dorsal lip of the blastopore into ventral region of another Xenopus gastrula leads to:
A. Normal development
B. Ventralization
C. Secondary body axis formation
D. Arrested gastrulation

26. In Drosophila, homeotic transformation of antenna into leg results from mutation in:
A. Ultrabithorax
B. Antennapedia
C. Bicoid
D. Kruppel

27. During chick limb development, grafting ZPA cells to anterior margin causes:
A. Limb loss
B. Mirror-image digit duplication
C. Random digit pattern
D. Shortened limb

28. If Noggin and Chordin are experimentally removed from Xenopus embryos, outcome will be:
A. Extra neural tissue
B. Absence of neural tissue (ventralized embryo)
C. Duplication of notochord
D. Expanded dorsal structures

29. In C. elegans, ablation of P2 cell leads to:
A. Duplication of pharynx
B. No posterior structures
C. Extra nervous system
D. Ventralization

30. A mutation in nanos gene of Drosophila will specifically affect:
A. Head formation
B. Thoracic segment identity
C. Abdomen formation
D. Wing development

31. Transplantation of Hensen’s node to the marginal zone of a chick embryo results in:
A. Arrested gastrulation
B. Secondary axis formation
C. Limb duplication
D. Extraembryonic membrane defects

32. Injection of bicoid mRNA into the posterior pole of a Drosophila embryo produces:
A. Two heads
B. No head
C. Extra thoracic segments
D. Ventralization

33. Blocking cortical rotation in Xenopus embryos leads to:
A. Dorsalized embryo
B. Ventralized embryo
C. Partial duplication of axes
D. Arrest at cleavage stage

34.

In vertebrate limb development, Sonic Hedgehog (SHH) from the zone of polarizing activity (ZPA) defines the anterior-posterior axis. If SHH-expressing cells are grafted to the anterior margin of a developing chick wing bud, which phenotype is expected?

A. Limb fails to develop
B. Limb develops with mirror-image duplication of digits
C. Only proximal structures will form
D. Normal limb with minor deformities

35.

In C. elegans, the P2 cell influences the fate of ABp but not ABa during early cleavage. If P2 is ablated (destroyed), which of the following outcomes will best describe the embryo?

A. Normal development due to redundant signaling.
B. Loss of posterior structures and abnormal cell fate in ABp.
C. Overproduction of mesodermal cells.
D. Formation of an additional gut primordium.

36.

During chick embryogenesis, the primitive streak defines the body axis. If a second primitive streak is induced experimentally by grafting Hensen’s node into the marginal zone, what will be the most likely result?

A. One embryo with two heads and a single tail.
B. Two embryonic axes forming a conjoined twin.
C. Arrest of development at the gastrula stage.
D. Only partial duplication of posterior structures.

37.

In Drosophila, a mutation in the bicoid gene leads to embryos lacking anterior structures. If mRNA of bicoid is injected into the posterior pole, which of the following will occur?

A. The embryo will develop two heads, one at each end.
B. The embryo will have no effect as posterior region suppresses bicoid.
C. The embryo will have duplicated thoracic and abdominal structures.
D. The embryo will die before gastrulation.

38.

In Xenopus embryos, the dorsal-ventral axis formation is initiated after fertilization. Suppose the cortical rotation is experimentally blocked by cooling the zygote immediately after fertilization. Which of the following outcomes is most likely?

A. Normal dorsal axis will form, as sperm entry already defines the dorsal side.
B. Embryo will develop with duplicated body axes.
C. Embryo will become ventralized, lacking neural structures.
D. The embryo will develop normally because zygotic transcription compensates.

39.

Apoptosis during digit formation in limb buds is controlled by:

A. FGF
B. BMP
C. Wnt
D. SHH

40.

The gradient of retinoic acid in vertebrate embryos regulates:

A. Dorsoventral axis
B. Left-right asymmetry
C. Anteroposterior axis
D. Neural crest migration

41.

Which molecule acts as an antagonist to BMP signaling in neural induction?

A. Wnt
B. FGF
C. Chordin
D. Retinoic acid

42.

Which experiment first proved the concept of embryonic induction?

A. Mangold–Spemann organizer graft
B. Drosophila bicoid gradient study
C. Chick limb bud rotation
D. Sea urchin fertilization block

43.

The process by which cells acquire different identities during development is called:

A. Differentiation
B. Competence
C. Determination
D. Morphogenesis

44.

Which morphogen gradient is responsible for dorsal structures in Xenopus?

A. BMP4
B. Wnt11
C. Chordin
D. Noggin

45.

Fate mapping of amphibian embryo is done using:

A. Radioactive markers
B. Vital dyes
C. Immunofluorescence
D. RNA probes

46.

The dorsal lip of the blastopore in amphibians is functionally equivalent to:

A. Organizer
B. Neural plate
C. Yolk plug
D. Animal pole

47.

Zona pellucida is digested by sperm enzyme:

A. Hyaluronidase
B. Acrosin
C. Trypsin
D. Collagenase

48.

In mammals, implantation occurs at which stage of embryonic development?

A. Blastula
B. Morula
C. Gastrula
D. Late cleavage

49.

Which gene family plays a crucial role in pattern formation along the anterior–posterior axis?

A. Pax genes
B. Hox genes
C. Notch genes
D. Wnt genes

50.

The neural crest cells give rise to all except:

A. Melanocytes
B. Adrenal medulla
C. Peripheral neurons
D. Skeletal muscles

51.

The Spemann organizer functions by secreting:

A. Sonic hedgehog
B. BMP inhibitors
C. Retinoic acid
D. FGF

52.

In C. elegans, the cell lineage is invariant. The fate of each cell is determined by:

A. Cell position
B. Cell interactions only
C. Cell lineage and cytoplasmic determinants
D. Random differentiation

53.

During chick development, the primitive streak represents:

A. Site of gastrulation
B. Neural induction
C. Area pellucida formation
D. Yolk syncytial layer

54.

Which gene determines anterior-posterior polarity in Drosophila embryo?

A. Dorsal
B. Bicoid
C. Snail
D. Gurken

55.

The process of gastrulation in sea urchin involves:

A. Epiboly of vegetal cells
B. Invagination of vegetal plate
C. Ingression of animal cells
D. Convergent extension of mesoderm

56.

In Xenopus development, the organizer region corresponds to:

A. Animal pole
B. Blastopore lip
C. Neural plate
D. Grey crescent

57.

Which of the following molecules establishes dorsal–ventral polarity in Drosophila embryo?

A. Bicoid
B. Gurken
C. Dorsal
D. Nanos

58.

The grey crescent in amphibian eggs is formed due to:

A. Migration of cytoplasm towards the animal pole
B. Cortical rotation exposing lighter cytoplasm
C. Movement of yolk towards vegetal pole
D. Fertilization cone formation