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

Concept:

• The Class B Floral Organ Identity genes are necessary for the proper development of the petals and stamens normally found in the second and third whorls of the flower.
• The APETALA3 (AP3) and PISTILLATA (PI) MADS-box gene products likely interact as a heterodimer to specify the B function of the organ identity model.​

• Mutations in either AP3 or PI result in alterations in the 2nd and 3rd whorls, such that petals are replaced by sepals, and stamens are replaced by carpels.
• These 3rd whorl carpels often fuse together with the 4th whorl carpels to form an enlarged gynoecium.
• Consistent with their mutant phenotypes, AP3 and PI RNAs accumulate in the 2nd and 3rd  whorls, beginning at around stage 3 of flower development.
• In addition, constitutive expression of both AP3 and PI from the CaMV35S promoter leads to 1st whorl sepals developing as petals, and to stamens developing at the expense of the 4th whorl carpels.

​

Hence the correct answer is option 2​

The correct answer is Option 1 i.e. AP2 

Concept:

• Floral meristem initiates the formation of four different types of floral organs: sepals, petals, stamens, and carpels, in the form of concentric rings, called whorls. 
• All the meristematic cells in the apical dome are consumed for the initiation of the innermost organ called the carpel, leaving behind only floral primordia as the floral bud develops. 
• In flowers, the following whorls are present: Sepals, Petals, Stamen and Pistil
• Three types of genes regulate floral development:
  1. Floral organ identity genes - These directly controls the identity of the flower. Products of these genes are transcription factors that likely control the expression of other genes that are involved in the formation or functions of the floral organs.
  2. Cadastral genes - These are spatial regulators of floral identity genes as they set boundaries for the expression of floral identity genes. 
  3. Meristem identity genes - These genes are required for the initial induction of the organ identity genes. They are also considered to be positive regulators of floral organ identify genes.
• Five genes are known to control the floral organ identity - APETALA1(AP1), APETALA2(AP2), APETALA3 (AP3), PISTILLATA (PI) and AGAMOUS (AG).
• Because mutations in these genes lead to changes in the floral organ identity without affecting the initiation of the flower, hence, these genes are homoeotic genes. 
• These homeotic genes fall into three categories/ classes i.e., type A, type B, and type C, that define three different activities:
  1. Type A activity - this is encoded by AP1 and AP2 controls the identity of first (sepals) and second (petals) whorls. Loss of type A activity results in the formation of the carpel in the place of sepals and the formation of stamens in the place of petals.
  2. Type B activity - This is encoded by AP3 and PI and it controls the identity of second (sepals) and third (stamens) whorls. Loss of B activity results in the formation of sepals instead of petals and carpels instead of stamens.
  3. Type C activity- this is encoded by AG and it controls activity in the third (stamens) and fourth(carpels) whorls of the flower. Loss of type C activity results in the formation of petals instead of stamens and the replacement of fourth whorls by the development of new flowers. 

Explanation:

• Most of the plant homeotic genes belong to a class of related sequences called MADS-box genes. 
• Many of the genes that determine the floral organ identity are MADS-box genes. 
• AP1, AP3/PI and AG are examples of MADS-box genes. 
• AP2 is the exception to this, it is not a MADS-box gene. 

Hence, the correct answer is Option 1. 

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  A and D

Explanation:

(A) Correct: Notch signaling is known for its role in lateral inhibition, which is a process where cells adopting a particular fate inhibit their neighbors from adopting the same fate. In the context of C. elegans, activation of Notch signaling in a VPC leads it to adopt a secondary cell fate, thereby preventing it from becoming a primary vulval cell.
(B) Incorrect: Notch signaling does not induce primary cell fate; it is actually responsible for inducing secondary fates in VPCs that are adjacent to the primary cell fate VPC.
(C) Incorrect: This statement is true but stated inversely here; the lack of Notch signaling can lead a cell to adopt a primary fate, but typically, Notch signaling inhibits primary fate to promote secondary fate adoption.
(D) Correct: LIN-12, the Notch receptor in C. elegans, is essential for the lateral communication between VPCs. This communication is critical for ensuring the proper distribution of primary, secondary, and tertiary fates among the VPCs.

The correct answer is Option 4

Explanation:

• Option 1 is incorrect because while cell movement and changes in position can occur during the development of multicellular organisms, including both angiosperms and gymnosperms, this is not a significant differentiating factor in their early development.
• Option 2 is incorrect because a suspensor, which is a structure that helps in pushing the developing embryo into the nutritive tissue of the seed, can form in both angiosperms and gymnosperms. It is not unique to angiosperms.
• Option 3 is not a defining difference between angiosperms and gymnosperms. Both groups can undergo cellular divisions where cell walls are formed between daughter nuclei after the initial cell divisions in the zygote. This description more broadly concerns differences in types of embryonic development, such as free-nuclear (initially lacking cell walls) versus cellular, but does not accurately distinguish between all angiosperms and gymnosperms.
• Option 4 accurately reflects a difference in the early development of angiosperms and gymnosperms regarding the orientation of the embryo. In gymnosperms, the shoot apical meristem (the region that will give rise to the future shoot) forms near the micropyle (the opening in the ovule through which the pollen tube typically enters). In contrast, in angiosperms, the shoot apical meristem forms at the end of the embryo opposite the micropyle. This difference is related to the overall orientation and development patterns of the embryos in each group

In gymnosperms, the early development of the embryo occurs with the formation of the Shoot apical meristem  near the micropyle. This means that as the embryo grows, the region that will become the future shoot system develops close to the point of entry for the sperm cells. This orientation is linked to the gymnosperms' evolutionary context and their specific embryological processes, such as the development of a suspensor that pushes the embryo into the nutritive tissue of the seed.

In contrast, angiosperms exhibit an opposite orientation. The SAM forms at the end of the embryo away from the micropyle. This orientation reflects the angiosperms' evolutionary adaptations and differences in how the embryo develops within the seed. The angiosperm seed structure and embryogenesis are such that the embryo is "turned around" compared to gymnosperms, with the future shoot system developing away from the micropyle.

Conclusion:

Therefore, the correct answer is Option 4

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 Petals and Carpels

Explanation:

E-class homeotic genes in Arabidopsis thaliana are essential for the development of various floral organs. These genes, also known as SEPALLATA (SEP) genes, play a critical role in specifying the identity of all four types of floral organs (sepals, petals, stamens, and carpels) by interacting with other classes of homeotic genes (A, B, and C).

SEPALLATA genes (SEP1, SEP2, SEP3, and SEP4) are required for the proper development and identity of petals, stamens, and carpels.
In the classical ABC model of flower development, E class genes (SEPALLATA genes) work in combination with A, B, and C class genes to specify the identity of the floral organs:

• A + E specify sepals.
• A + B + E specify petals.
• B + C + E specify stamens.
• C + E specify carpels.

 

Fig:  ABCE model for floral organ determination in which SEPs act as Class E genes required for floral organ identity. (Source: Taiz)