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

Key PointsTypes cell movements in gastrulation - 

• Although gastrulation patterns exhibit enormous variation throughout the animal kingdom, they are unified by the five basic types of cell movements that occur during gastrulation:

1. Invagination
   • Infolding of a sheet (epithelium) of cells, much like the indention of a soft rubber ball when it is poked.
   • Examples: Sea urchin endoderm
2. Involution
   • Inward movement of an expanding outer layer so that it spreads over the internal surface of the remaining external cells.
   • Examples: Amphibian mesoderm
3. Ingression
   • Migration of individual cells from the surface into the embryo’s interior. Individual cells become mesenchymal (i.e., separate from one another) and migrate independently.
   • Examples: Sea urchin mesoderm, Drosophila neuroblasts
4. Delamination
   • Splitting of one cellular sheet into two more or less parallel sheets. While on a cellular basis it resembles ingression, the result is the formation of a new (additional) epithelial sheet of cells. 
   • Examples: Hypoblast formation in birds and mammals
5. Epiboly
   • Movement of epithelial sheets (usually ectodermal cells), spreading as a unit (rather than individually) to enclose deeper layers of the embryo.
   • Can occur by cells  dividing, by cells changing their shape, or by several layers of cells intercalating into fewer layers; often, all three mechanisms are used.
   • Examples: Ectoderm formation in sea urchins, tunicates, and amphibians

Hence the correct answer is option 4.

The correct answer is Option 4 i.e.A - iii; B - i; C - iv; D - ii

Explanation-

Isolecithal:

• In Isolecithal eggs, the yolk is evenly distributed throughout the cytoplasm.
• These eggs often have a small to moderate amount of yolk, and cleavage can occur throughout the entire egg. Examples of animals with isolecithal eggs include many mammals and some marine invertebrates.

Mesolecithal:

• Mesolecithal eggs have a moderate amount of yolk that is concentrated at one pole (vegetal pole), while the rest of the egg contains less yolk.
• Cleavage tends to be uneven, with more cell division occurring in the region with less yolk. This type of egg is often seen in amphibians and some fish.

Centrolecithal:

• Centrolecithal eggs have the yolk concentrated at the center of the egg.
• Cleavage is superficial, occurring in a thin layer around the periphery of the egg, avoiding the centrally located yolk. This type of egg is found in insects and arthropods

Telolecithal :

• Birds undergo telolecithal cleavage.
• In telolecithal cleavage, the egg has a significant amount of yolk, which is concentrated at one pole (discoidal). Cleavage occurs in a small disc of the egg called the blastodisc.

Concept:

• The Bartholin’s glands (or greater vestibular glands) are important organs of the female reproductive system.
• Danish anatomist Caspar Bartholin Secundus first described them in 1677.
• Their primary function is the production of a mucoid secretion that aids in vaginal and vulvar lubrication.
• The glands are located in the vulvar vestibule, at either side of the external orifice of the vagina.
• They are homologous to the bulbourethral (Cowper’s) glands in males.

Explanation:

• The primary function of the Bartholin glands is the production of a mucoid secretion that lubricates the distal end of the vagina during intercourse.
• The glands become active after menarche and are non-palpable.
• Each gland is oval-shaped and measures, on average, 0.5 cm.
• A two-centimeter-long efferent duct connects each gland to the posterolateral aspect of the vaginal orifice (between the hymen and the labia minora).

 

hence the correct answer is option 1

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 Option 2 i.e. Genetic specificity of interaction.

Concept:

Determination:

• This is a term in developmental biology that refers to the point in the developmental process at which a cell or group of cells becomes committed to a particular fate.
• Once a cell's role is determined, the next steps are differentiation and morphogenesis which lead to the formation of a specific type of tissue or organ.
• However, this determination is not always irreversible.

Genetic specificity of interaction:

• This term refers to the concept that the fate of a cell or group of cells is determined by the specific genes they carry.
• Genetic specificity implies that every cell or piece of tissue carries a specific set of genetic information that governs its development and dictates what form and function it will have, regardless of its environment.
• When transplanted to a different location, these cells will still follow their inherent genetic program.

Regional specificity of interaction:

• This concept suggests that a cell's or tissue's developmental behavior and fate might depend on its location within the embryo.
• In other words, cells or tissues will interact with their immediate environment and adjust their developmental path based on these interactions.
• Here, the environment and cell-to-cell interactions can influence the developmental outcome and modify a cell's fate from what was genetically programmed.

Autonomous specification:

• This describes a mode of development in which the fate of a cell is established early on and is independent of interactions with neighboring cells.
• Essentially, certain cells in the early embryo are programmed to follow a specific developmental path, regardless of their surroundings.
• The genetic information in these cells directs them to form specific parts of the organism, even if they are isolated from the rest of the embryo or transplanted into a different region.
• This is similar to the concept of genetic specificity but places more emphasis on the independence of the developmental path from neighboring cell influence.

Explanation

• The transplanted frog tissue interacts with the newt embryo following the laws of its own species-specific developmental program.
• Despite being placed into a different region and species, the transplanted tissue commits to developing into the structure it was originally destined to become, as per its inherent genetic program.
• This shows that the developmental fate is attributed more to the genetic composition of the transplanted cells rather than the influence of their new location.
• The interaction between the gene expression in the transplanted cells and the new host's cells results in the development of frog-like mouth parts in the newt larvae, illustrating the concept of genetic specificity of the interaction.
• This is distinct from the concept of regional specificity of interaction which suggests that the fate of a cell or tissue is affected by its surrounding cells or tissues and will change its developmental path to match its new environment.
• In this case, the cells contributed to the structure they were originally "programmed" to create via genetic specification, not the structure typical of the region to which they were transplanted.

Hence the correct answer is Option 2

The correct answer is Option 3 i.e.β‐catenin will accumulate in the nuclei of all blastula cells leading to animal cells getting specified as endoderm and mesoderm.

Concept:-

• Beta-catenin acts as a transcription factor in wnt signaling.
• Beta-catenin is found throughout the embryo.
• Beta-catenin is Active on the dorsal side.
• GSK-3 inhibits Beta-catenin at the ventral side.
•  During fertilization, Dsh and Wnt 11 protein from the vegetal pole translocated to the dorsal side of the egg.
• Disheveled (Dsh) inhibits Gsk-3, thereby activating Beta-catenin.

Explanation:-

Option 1:- β‐catenin accumulation in the nuclei of large micromeres will be inhibited leading to formation of ectodermal ball.

• GSK-3 inhibits beta-catenin. if GSK-3 is blocked, beta-catenin will be free, which will enter each nucleus of the vegetal pole and will form endoderm and mesoderm.
• ​  Hence, this statement is incorrect.   

Option 2:-  β‐catenin will accumulate in the nuclei of all blastula cells leading to an ectodermal ball.

• If beta-catenin will accumulate, it will form an endoderm and mesoderm, not the ectodermal ball.
•  Hence, this option is incorrect.

Option 3:- β‐catenin will accumulate in the nuclei of all blastula cells leading to animal cells getting specified as endoderm and mesoderm.

• Beta-catenin will get accumulated in the nuclei of all blastula cells which was earlier inhibited by GSK-3. Therefore, beta-catenin will form endoderm and mesoderm.
• Hence, this option is correct.

Option 4:- β‐catenin which accumulates in the nuclei of large micromeres will be inhibited leading to animal cells getting specified as endoderm and mesoderm.

• If GSK-3 is blocked, beta-catenin will enter each nucleus of all dorsal cells, it will not get inhibited.
• Hence, this option is incorrect.