Human sperms are allowed to fertilize ova having non functional ovastacin. The following possibilities may be of significance in the fusion of these gametes:
(a) The sperms will not fertilize ova.
(b) The sperms will blind and penetrate the zona pellucida but will not be able to fuse with ovum membrane.
(c) ZP2 will not be clipped by cortical granuel protease.
(d) CD9 protein of egg membrane microvilli will not be able to interact with sperm membrane proteins in the absence of ovastacin.
(e) Polyspermy may occur frequently.
Which combination of statements represent the outcome of the event?
(a) and (b)
(a) and (e)
(c) and (d)
(b) and (e)
B.
(a) and (e)
The mouse zona pellucida is composed of three glycoproteins (ZP1, ZP2 and ZP3) of which ZP2 is proteolytically cleaved after gamete fusion to prevent polyspermy. This cleavage is associated with exocytosis of corteical granules that are peripherally located subcellular organelles unique to ovulated eggs. Ovastacin is an oocyte-specific memeber of the astacin family of metalloendoproteases. Using specific antiserum, ovastacin is detected in cortical granuels before, but not after, fertilization. Recombinant ovastacin cleaves ZP2 is a direct substrate of this metalloendoprotease. Female mice lacking ovastacin does not cleave ZP2 after fertilization, and mouse sperm binds equally well to ovasstacin lacking two-cell embroys; as they did to normal eggs.
Since non-functional ovastacin containing ova were selected, ZP2 will not be cleaved, and so ther will be constant chances of polyspermy. The sperm egg binding will not be affected, as the cortical reaction takes place after the membrabane fusion. Once a sperm has penetrated the egg, evastacin from cortical vesicles initiates zona hardening to prevent polyspermy.
Following statements were made with respect to symbiotic association of rhizobia with legumes:
(a) nodD is regulatory gene.
(b) Nod factors are lipochitin oligosaccharides.
(c) Nod factors predominantly have α-1→ 4 linked N-acetyl-D-glucosamine backbone.
(d) Receptors for Nod factors are protein kinases with extracellular sugar-binding Lys M domain.
Which one of the following combinations represents all correct statements?
(a),(b) and (c)
(a),(c) and (d)
(b),(c) and (d)
(a),(b) and (d)
Following are certain statements regarding apomixis in plants:
(a) Apomixis cannot be used to mantain hybrid vigor over many generations in plants
(b) In sporophytic apomixis maternal genotype is maintained
(c) There is an event of meiosis during gametophytic apomixis and is also referred as apomeiosis
(d) In diplospory, meiosis of the megaspore mother cell is aborted, resulting in two unreduced spores, out of which one forms the female gametophyte
Which one of the following combinations is correct?
(a) and (b)
(a) and (c)
(b) and (c)
(b) and (d)
In which stage of Arabidopsis embryogensis is hypophysis first observed?
Octant
Dermatogen
Globular
Transition
Given below are some statements related to lower eumetazonas. Select the INCORRECT statement.
Ctenphores are diploblastic with radial symmetry
Placozonas, with weakly differentiated tissue layers, are not diploblasts
Cnidarians are diploblastic with typically two stages in their life cycle.
Hydrozonas, a Cnidarian class, often have colonial polyps in their life cycle
In case of hydra, the major head inducer of the hypostome organizer is a set of Wnt proteins acting through the canoniocal β-catenin pathway. What would be the result, if a transgenic Hydra is made to globally misexpress the downstream Wnt effector β-catenin?
Ectopic buds will be formed all along the body axis and even on the top of the newly formed buds
Ectopic tentacles form at all levels
Both ectopic tentacles and buds would be formed along the body axis
There woulod be no change observed
The following assumptions were derived from the above experiment:
(a) Medium A contained bFGF and PDGF.
(b) Medium b contained retinoic acid.
(c) Cells cultured in medium B were determined to become functional neurons prior to addition of the medium.
Which one of the following combinations represents correct statements?
(a) and (b) only
(a), (b) and (c)
(b) and (c) only
(a) and (c) only
Given below are some of the statements regarding regeneration:
(a) The type of regeneration characteristic of mammalian liver is considerd as Compensatory regeneration
(b) Regrowth of hair shaft from follicular cells exemplifies stem cell mediated regeneration
(c) Regeneration occuring through the repattering of existing tissues with little new growth is known as morphallaxis
(d) Adult structures undergoing dedifferentiation forming a blastema, that then redifferentiates to form the lost structure, is called epimorphosis
Choose the most appropriate combination of correct statements:
(d) only
(c) and (d) only
(a) , (b) and (c) only
(a) , (b) , (c) and (d)
Both TGF-β are Sonic hedgehog signals play important roles in both neuralation and cellfate patterning of the neural tube. Which one of the following statements is true?
High levels of BMP specifiy the cells to become epidermis
Very low levels of BMP specify the cells to become epidermis
High levels of BMP specifiy the cells to become neural plate
Intermediate levels of BMP do not effect the formation of neural crest cells
The zygote of C.elegans exhibits rotational cleavage. When the first two blastomeres formed (P1 and AB) are experimentally seperated, the following outcomes may be possible:
(a) The P1 cell in isolation generates all the cells it would normally make, showing autonomous specification
(b) The P1 cell in isolation generates all the cells it would normally make, showing conditional specfication
(c) The AB cell is isolation generates a small fraction of cell types it would normally make, showing conditional specification
(d) The AB cell in isolation generates a small fraction of cell types it would normally make, showing autonomous specification
Which one of the above combination of statements is true?
(a) and (c)
(b) and (c)
(b) and (d)
(a) and (d)
