Developmental Biology MCQ Quiz in বাংলা - Objective Question with Answer for Developmental Biology - বিনামূল্যে ডাউনলোড করুন [PDF]

The vulva is a part of female sex apparatus, the positional information needed by the vulva progenitor cells is provided by a cell within the gonad called anchor cell. In absence of anchor cell a vulva does not develop. The signal that commits p5-p and p7p to their secondary fates might not come directly from the anchor cell but via p6p in the form of a different extracellular signaling compound.

The correct answer is Option 1 i.e. Epiboly.

Concept:

• Gastrulation is the process of coordinated movements of cells and tissues wherein the cells of the blastula are rearranged dramatically.
• There are numerous cells present in the blastula and their position is determined during the cleavage.
• During gastrulation, these cells are rearranged to get new position and new neighbouring cells. 
• The cells that will form the endoderm and mesoderm are brought inside the embryo whereas the cells that will form the skin and nervous system are spread across the outer surface. 
• This gastrulation results in the formation of three germ layers - outer ectoderm, inner endoderm and interstitial mesoderm.
• This also set stage for the interaction between the cells 
• Entire embryo participates in the gastrulation process and the movement in the different parts is coordinated.
• Gastrulation involved following movement - invagination, involution, regression, delamination and epiboly. 

Important Points

Epiboly - 

• Epiboly is the expansion of one sheet of cells over another sheet of cells.
• The epithelial cells are spread such that they enclose the deeper layers (endoderm and mesoderm). 
• It involves the movement of the blastula cells that will form the ectoderm.
• Hence, this is the correct option.

Emboly - 

• It is the first process in gastrulation and it is also called internalisation. 
• In this process the cells of blastula that will become endoderm and mesoderm are arranged below the layer of cells that will becomes the ectoderm.
• So involved the movement of cells that will form endoderm and mesoderm.
• Hence, this is an incorrect option.

Involution - 

• Involution is the inward movement of the expanding outer layer so as to spread across the inner surface of the external cells.
• Hence, this is an incorrect option.

Ingression - 

• Ingression is the individual migration of the cells from the surface layer towards the interior.
• Hence, this is an incorrect option.

Hence, the correct answer is option 1.

The correct answer is The release of the cortical granules after sperm entry converts the vitelline membrane into the fertilization membrane which blocks polyspermy.

Explanation:

The cortical reaction is a crucial event in the process of fertilization, particularly in sea urchins, and it plays a key role in preventing polyspermy (the entry of more than one sperm into the egg).

• After sperm entry, cortical granules located just beneath the plasma membrane of the egg are released (exocytosis) into the space between the plasma membrane and the vitelline membrane.
• The contents of these cortical granules modify the vitelline membrane, converting it into the fertilization membrane, which serves as a physical barrier that prevents additional sperm from entering the egg, thus blocking polyspermy.

Other Options:

• The entry of Ca²⁺ ions into the egg initiates development: While calcium is crucial for initiating the cortical reaction, development is not initiated solely by calcium entry.
• The exocytosed cortical granules during egg maturation contain components of the zona pellucida: Sea urchins do not have a zona pellucida; this structure is present in mammals. The correct term here is vitelline membrane in sea urchins.
• The depolarization of the plasma membrane after sperm entry helps to block polyspermy: This is related to the fast block to polyspermy, which occurs immediately after sperm entry, but it is not related to the cortical reaction (which is the slow block).

Thus, Option 4 correctly describes the role of the cortical reaction in preventing polyspermy by forming the fertilization membrane.

The correct answer is It leads to digestion of the zona pellucida.

Concept:

The acrosomal reaction is a critical step in the process of fertilization, where the sperm interacts with the outer layers of the egg to allow its entry.

What is the Acrosomal Reaction?

• The acrosomal reaction occurs when the sperm comes into contact with the egg's outer layer, specifically the zona pellucida in mammals (or the vitelline envelope in non-mammalian species).
• The reaction involves the release of hydrolytic enzymes from the acrosome, which is a specialized vesicle at the tip of the sperm cell.
• These enzymes digest the zona pellucida, allowing the sperm to penetrate this layer and eventually reach the egg's plasma membrane for fertilization.

Explanation:

"It is a repulsive interaction between the sperm and the egg."

• This statement is incorrect. The acrosomal reaction is not a repulsive interaction; it is a mechanism that facilitates the interaction between the sperm and the egg.

"It involves digestion of the acrosome by the sperm when it encounters an egg."

• This statement is incorrect. The acrosome itself is not digested. Instead, it releases enzymes that help digest the zona pellucida of the egg.

"It leads to digestion of the zona pellucida."

• This statement is correct. The acrosomal reaction releases enzymes that digest the zona pellucida, allowing the sperm to penetrate and reach the egg's plasma membrane.

"It is the fusion of the sperm and egg plasma membranes."

• This statement is incorrect. The fusion of the sperm and egg plasma membranes occurs after the acrosomal reaction and sperm penetration. The acrosomal reaction itself is a separate event that facilitates this fusion.

Conclusion: The correct answer of the acrosomal reaction is It leads to digestion of the zona pellucida. This process is essential for the sperm to penetrate the egg's outer layers and proceed with fertilization.

The correct answer is Option 3

Concept: 

Autonomous Specification:

• Autonomous specification refers to the inherent ability of a cell or group of cells to differentiate into specific cell types based on their intrinsic factors or developmental program.
• Cells have the inherent potential to follow a predetermined developmental pathway and differentiate into specific cell types without relying heavily on external signals or interactions with neighboring cells.
• Autonomous specification is often associated with the early stages of embryonic development, where cells possess predetermined information or cues that guide their differentiation.

• One classic example of autonomous specification involves the early development of the nematode Caenorhabditis elegans.

Example in C. elegans:

• During the early embryogenesis of C. elegans, certain cells inherit specific cytoplasmic determinants. These determinants are molecules often proteins or RNAs that are unequally distributed in the parent cell and become segregated into particular daughter cells during division.
• For example, the muscle cell fate in C. elegans is determined by the segregation of muscle fate determinants. These determinants are factors that promote the expression of muscle-specific genes in the cells that inherit them.
• Therefore, the fate of these cells is "autonomously" determined; it does not depend on signals from other cells but relies on the inheritance of these internal determinants. This shows how the developmental pathway of a cell can be preset by its lineage and the specific molecules it inherits during cell division.

Conditional Specification:

• Conditional specification implies that the fate or differentiation of cells is influenced by external conditions, signals, or interactions with neighboring cells.
• Cells may require specific signals, cues, or environmental factors to trigger their differentiation into particular cell types. In the absence of these external influences, the fate of the cells may be different.
• Conditional specification is often observed in later stages of development, where cell fate decisions are influenced by the surrounding microenvironment or interactions with adjacent cells.

Example with Notch-Delta signaling in Drosophila:

• The Notch-Delta signaling pathway is a well-studied example of conditional specification, playing a critical role in the development of many organisms, including the fruit fly Drosophila melanogaster.
• Specifically, in Drosophila neurogenesis (the development of the nervous system), the Notch-Delta signaling pathway helps determine which cells become neurons and which become epidermal cells. Cells express the Delta ligand on their surface, which can bind to the Notch receptor of neighboring cells.
• When a cell's Delta ligand binds to the Notch receptor of an adjacent cell, it inhibits the tendency of that neighboring cell to also become a neuron, promoting its development into epidermal tissue instead. This interaction ensures a balanced distribution of neuronal and epidermal cells.
• Thus, the fate of cells in this system is conditional upon their interactions with neighboring cells, unlike the inherited determinants seen in autonomous specification.

Fig:- (A) - Autonomous specification in the early tunicate embryo. When the four blastomere pairs of the 8-cell embryo are dissociated, each forms the structures it would have formed had it remained in the embryo. (B) - Conditional specification- cell becomes depends on its position in the embryo. Its fate is determined by interactions with neighboring cells. (Source:- Gilbert 12^th edition)

Explanation: 

Autonomous specification refers to a mechanism by which a cell's fate is determined early in development by factors that are internally localized within the cell or its precursors, without requiring further input from its environment or neighbors. An example is the predetermined fate of cells in C. elegans due to the segregation of specific cytoplasmic determinants. In contrast, conditional specification relies on the interaction between cells, where a cell's fate is not predetermined but instead influenced by signals from its neighbors. The Notch-Delta signaling pathway is a well-documented example of this, playing a crucial role in various developmental processes including the determination of cell differentiation in the neural development of Drosophila (fruit flies). This choice appropriately highlights the key differences in the implementation of autonomous and conditional specification

Conclusion:

Therefore, the correct answer is Option 3

 

 Key Points

• Hydra is one of the few organisms that possess tremendous regeneration potential, capable of regenerating complete organism from small tissue fragments or even from dissociated cells.
• This peculiar property has made this genus one of the most invaluable model organisms for understanding the process of regeneration.

ROUTINE CELL REPLACEMENT BY THREE TYPES OF STEM CELLS

• A hydra’s body is not particularly stable.
• In humans and flies, for instance, a skin cell in the body’s trunk is not expected to migrate and eventually be sloughed off from the face or foot, but that is exactly what happens in hydra.
• The cells of the body column are constantly undergoing mitosis and are eventually displaced to the extremities of the column, from which they are shed.
• Thus, each cell plays several roles, depending on how old it is, and the signals specifying cell fate must be active all the time. In a sense, a hydra’s body is always regenerating.
• This cellular replacement is generated from three cell types.
• Endodermal and ectodermal cells are unipotent progenitor cells that divide continuously, producing more lineage-restricted epithelia.
• The third cell type is a multipotent interstitial stem cell found within the ectodermal layer.
• This stem cell generates neurons, secretory cells, nematocytes, and gametes.
• The most significant cell proliferation by each of these three types of stem cells occurs within the central region of the body, after which displaced myoepithelia and migrating interstitial progeny move to and differentiate at the apical and basal extremities.
• Compared with the myoepithelial stem cells (endoderm and ectoderm), interstitial stem cells are paused in G2 phase of the cell cycle for a longer period and cycle at a faster rate, suggesting that the interstitial stem cells are poised to immediately respond to a need for cell replacement through rapid proliferation.
• These three cell types are all that are needed to form a hydra, and if hydra cells are separated and reaggregated, a new hydra will form.

 

Explanation:

• Endodermal and ectodermal cells are unipotent progenitor cells that divide continuously, producing more lineage-restricted epithelia.
• The third cell type is a multipotent interstitial stem cell found within the ectodermal layer.

Hence the correct answer is option 3.

Key Points

• Hydra is one of the few organisms that possess tremendous regeneration potential, capable of regenerating complete organism from small tissue fragments or even from dissociated cells.
• This peculiar property has made this genus one of the most invaluable model organisms for understanding the process of regeneration.

ROUTINE CELL REPLACEMENT BY THREE TYPES OF STEM CELLS

• A hydra’s body is not particularly stable.
• In humans and flies, for instance, a skin cell in the body’s trunk is not expected to migrate and eventually be sloughed off from the face or foot, but that is exactly what happens in hydra.
• The cells of the body column are constantly undergoing mitosis and are eventually displaced to the extremities of the column, from which they are shed.
• Thus, each cell plays several roles, depending on how old it is, and the signals specifying cell fate must be active all the time. In a sense, a hydra’s body is always regenerating.
• This cellular replacement is generated from three cell types.
• Endodermal and ectodermal cells are unipotent progenitor cells that divide continuously, producing more lineage-restricted epithelia.
• The third cell type is a multipotent interstitial stem cell found within the ectodermal layer.
• This stem cell generates neurons, secretory cells, nematocytes, and gametes.
• The most significant cell proliferation by each of these three types of stem cells occurs within the central region of the body, after which displaced myoepithelia and migrating interstitial progeny move to and differentiate at the apical and basal extremities.
• Compared with the myoepithelial stem cells (endoderm and ectoderm), interstitial stem cells are paused in G2 phase of the cell cycle for a longer period and cycle at a faster rate, suggesting that the interstitial stem cells are poised to immediately respond to a need for cell replacement through rapid proliferation.
• These three cell types are all that are needed to form a hydra, and if hydra cells are separated and reaggregated, a new hydra will form.

 

 

Explanation:

• Compared with the myoepithelial stem cells (endoderm and ectoderm), interstitial stem cells are paused in G2 phase of the cell cycle for a longer period and cycle at a faster rate, suggesting that the interstitial stem cells are poised to immediately respond to a need for cell replacement through rapid proliferation.

Hence the correct answer is option 4

Concept:

• The MADS-domain transcription factors are crucial for flower organ specification in plants.
• Among the following plant homeotic genes, AP1 (APETALA1) does not code for a MADS-domain transcription factor necessary for flower organ specification.
• MADS-domain transcription factors are a family of DNA-binding proteins that play crucial roles in plant development, particularly in the specification of floral organ identity.
• The term "MADS" is an acronym derived from the names of the original four genes identified in which this domain was found: MCM1 (from yeast), AG (AGAMOUS), DEFICIENS (from Antirrhinum), and SRF (serum response factor).
• MADS-domain transcription factors contain a conserved DNA-binding domain called the MADS (MCM1, AGAMOUS, DEFICIENS, SRF) domain. This domain is characterized by a region of approximately 60 amino acids that forms a DNA-binding and dimerization module.
• The MADS domain allows these transcription factors to bind to specific DNA sequences called MADS-box elements in the promoters of target genes.

Explanation:

• AP1 is a floral meristem identity gene in Arabidopsis thaliana and belongs to the APETALA1/FRUITFULL (AP1/FUL) subfamily of MADS-box genes.
• It plays a role in specifying sepal and petal identity in the first two whorls of floral organs.
• However, AP1 does not directly encode a MADS-domain transcription factor.
• Instead, it encodes a protein with a different DNA-binding domain called the AP1 domain, which is structurally distinct from the MADS domain.
• The other plant homeotic genes mentioned, such as AP3 (APETALA3), AG (AGAMOUS), and PI (PISTILLATA), do code for MADS-domain transcription factors.
• AP3 and PI are involved in specifying petal and stamen identities, while AG is crucial for specifying stamen and carpel identities in the floral organ development process

 

Concept:

• Tetrapod limbs appear to have evolved by appropriating and modifying a spatial regulation system that originated in our shared ancestor with modern fish.
• It's a fantastic evolutionary tale that poses intriguing issues regarding how homology is defined.
• During limb development in tetrapods (four-limbed vertebrates), the AER is a specialized region located at the distal end of each developing limb bud.
• The AER is a thickened ridge of ectodermal tissue that interacts with the underlying mesenchymal cells to promote limb outgrowth and determine the overall pattern of the limb.

Explanation:

• In an apical ectodermal ridge (AER), the presence of the Zone of Polarizing Activity (ZPA) is necessary for the production of a functional appendage in tetrapods.
• Within the AER, the ZPA is a specific region that plays a crucial role in establishing the anterior-posterior (AP) axis of the limb and determining its pattern.
• The ZPA is located in the posterior part of the limb bud and contains a signaling molecule called Sonic Hedgehog (Shh).
  • The production of Sonic Hedgehog by the ZPA is essential for the proper development and patterning of the limb.
  • Sonic Hedgehog acts as a morphogen, a signaling molecule that forms a concentration gradient within the developing tissue.
  • The concentration gradient of Sonic Hedgehog influences the expression of specific genes in the surrounding cells, leading to the establishment of different positional identities along the AP axis of the limb.
• The presence of the ZPA and its production of Sonic Hedgehog are crucial for several aspects of limb development, including:
  • Anterior-Posterior Axis Patterning:
    • Sonic Hedgehog signaling from the ZPA determines the anterior-posterior positional identity of the developing limb.
    • Different levels of Sonic Hedgehog concentration result in the formation of different digit identities along the length of the limb.
    • For example, higher concentrations of Sonic Hedgehog promote the formation of posterior digits, while lower concentrations contribute to the formation of anterior digits.
  • Digit Number and Identity:
    • The ZPA and Sonic Hedgehog signaling play a role in specifying the number and identity of digits.
    • By establishing a gradient of Sonic Hedgehog expression, the ZPA helps determine the number and location of digit primordia along the AP axis.
    • This process is crucial for the formation of the appropriate number and arrangement of functional fingers or toes.
  • Limb Outgrowth:
    • The AER, including the ZPA, is also involved in promoting limb outgrowth.
    • The AER acts as a signaling center that stimulates the proliferation of underlying mesenchymal cells, contributing to the elongation and extension of the limb bud.
    • This coordinated growth is necessary for the proper formation of a functional appendage.
  • In summary, the presence of the Zone of Polarizing Activity (ZPA) in the apical ectodermal ridge (AER) is necessary for the production of a functional appendage in tetrapods.
  • The ZPA, through the production of Sonic Hedgehog, is involved in establishing the anterior-posterior axis, specifying digit number and identity, and promoting limb outgrowth.
  • These processes are crucial for the development of a properly patterned and functional limb in tetrapods.

Hence the correct answer is option 1

Concept:

• Izumo and Juno are two proteins that play critical roles in mediating the interaction between sperm and egg.
• In order for fertilization to occur, there must be specific recognition and binding between the sperm and egg.
• Izumo, located on the surface of the sperm, interacts with Juno, located on the surface of the egg.
• This interaction is essential for the fusion of sperm and egg membranes, leading to fertilization.

Important Points

• To demonstrate that Izumo and Juno interact with each other, an in vivo experiment using cell lines expressing these proteins can be conducted.

Option 1 - INCORRECT

• It focuses on the absence of Izumo in sperm and assumes that fertilization will not occur without Izumo.
• However, it does not directly address the interaction between Izumo and Juno, which is the specific focus of the question.

Option 2 - INCORRECT

• This experiment would provide information about the localization of Izumo on sperm and Juno on eggs.
• However, the presence of these proteins on their respective cells does not necessarily indicate that they interact with each other.

Option 3 - INCORRECT

• Although this option utilizes a fluorescence resonance energy transfer (FRET) assay, which can indicate a physical interaction between proteins, it does not provide in vivo evidence of the interaction between Izumo and Juno.
• This approach involves mixing purified Izumo and Juno proteins in a tube, which does not accurately reflect the complex cellular environment in which the interaction occurs during fertilization.

Option 4 - CORRECT

• Here, two independent kidney cell lines are developed: one expressing Izumo and the other expressing Juno.
• When these two cell lines are mixed together, they tend to aggregate with each other.
• This aggregation indicates that the Izumo-expressing cells are interacting with the Juno-expressing cells.
• The aggregation is likely a result of the specific binding between Izumo and Juno, mimicking the interaction that occurs between sperm and egg during fertilization.
• This experiment provides evidence that Izumo and Juno interact with each other, as the presence of both proteins on the cell surfaces leads to cell-cell adhesion and aggregation.

Hence, the correct answer is option 4.