Developmental Biology MCQ Quiz in मल्याळम - Objective Question with Answer for Developmental Biology - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

The correct answer is (C) → (A) → (B) → (D)

Concept:

The fusion of haploid male gamete (sperm) to haploid female gamete (ovum) to form diploid zygote is called fertilization.

The events of fertilization usually include

1. contact and recognition between sperm and egg;
2. regulation of sperm entry into the egg;
3. fusion of genetic material from the two gametes; and
4. activation of egg metabolism to start development.

Explanation: 

The process preceding to fertilization involves following steps.

1. Chemoattraction of sperm to the egg by chemicals secreted by egg.
2. Binding and interaction of sperm to vitelline membrane
3. Passage of sperm through extracellular envelope.

Statement A: release of enzymatic contents from the acrosomal vesicle through exocytosis

• The acrosome reaction releases enzymes exocytotically. 
• These proteolytic enzymes digest the egg’s protective coating, allowing the sperm to reach and fuse with the egg cell membrane.
• acrosome reaction in amphibians and mammals almost same
• this reaction starts only with interaction of ZP binding receptors on sperm interact with ZP proteins on egg membrane. 

​Fig 1: Acrosome Reaction

 

Statement B: binding and interaction of the sperm to vitelline membrane

• Surrounding the egg cell membrane is an extracellular layer often used in sperm recognition.
• In most animals, this extracellular layer is the vitelline envelope.
• In mammals, it is the much thicker zona pellucida.
• Cortical granules lie beneath the egg’s cell membrane.

Statement C: chemoattraction of the sperm to the egg by soluble factors secreted by egg

• Species-specific chemotactic molecules secreted by the egg can attract sperm that are capable of fertilizing it.
• In sea urchins, the chemotactic peptides resact and speract have been shown to increase sperm motility and provide direction toward an egg of the correct species

Statement D: Passage of sperm through extracellular envelope.

• After acrosome reaction, secondary binding of sperm and egg takes place and part of egg membranes are degraded by enzymes of sperm 
• this paves way for sperm head whereas tail piece remains outside and membrane of egg hardens to avoid polyspermy.

Fig 2: Mechanism of Passage of sperm through extracellular envelope of egg.

 

So, the correct answer is option 4 and the sequence is  (C) → (A) → (B) → (D)

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 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

 

The Correct Answer is Option 2: Abnormalities of the hands and feet wherein the digits fuse.

Concept: Developmental Biology (Limb Development)

HOX genes: These genes specify the identity of the limb region and are a homeobox transcription factor. Homeobox transcriptional factors play a major role in body patterning and embryonic patterning.

Functions of Hox genes:

• Primarily responsible for specifying the location of the formation of limbs and specifying mesenchymal cells into stylopod, zeugopod, and autopod.
• Hox genes are also responsible for the zone of polarizing activity and digits formation (fingers).
• Hox genes and specification:
  • Hox 9, 10: stylopod (Femur and Humerus)
  • Hox 11: zeugopod (ulna and radius, tibia and fibula)
  • Hox 12, 13: autopod (ankles and toes, wrists and fingers)

Mutations:

• Hoxa12 (HOXA13): This mutation is known to cause hand-foot-genital syndrome. The person having this mutation will have deformed fingers and toes.
• Hox 11 knockout: Zeugopod will not form.
• Hox 13 knockout: Autopod will not form.
• Hoxd13 (HOXD13): People with this mutation is known to have the mutations of hand and feet where their digits fuse.

Explanation:

1. Since HOXD13 gene is not responsible for zeugopod formation, this option is incorrect.
2. Humans homozygous for the HOXD13 gene mutation is known to have deformities of the hands and feet where the digits fuse. This disease is known as Synpolydactyly. Therefore, this option is correct.
3. Since Hox 9 and Hox 10 are responsible for the stylopod, HOXD13 will not affect it. Therefore, this option is also incorrect.
4. HOXD13 is not related to proximal regions of limbs. Therefore, this option is incorrect.

Conclusion: A homozygous mutation in HOXD13 is associated with the abnormalities of the limbs (hand and feet), the digits also fuse in this condition, which makes option B the correct answer.

 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