127 public questions tagged with this topic.
The cortical reaction, which occurs immediately after the first sperm fuses with the oocyte, causes changes in the zona pellucida that prevent further sperm penetration.
Ref: NCERT Biology Textbook for Class XI and XII (Zoology section), Chapter: Biology - Zoology portion covering relevant system and function.
Following fertilization, the zygote undergoes cleavage, forming a morula before further development into a blastocyst. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Zoology section), Chapter: Biology - Zoology portion covering relevant system and function.
Double fertilization is unique to flowering plants; one sperm fuses with the egg to form a diploid zygote, while the other fuses with the two polar nuclei to form a triploid endosperm, which nourishes the developing embryo.
Ref: NCERT Biology Textbook for Class XI and XII (Botany section), Chapter: Morphology and Anatomy of Flowering Plants, Topic: Plant structure and tissue systems.
The acrosomal reaction releases enzymes that digest the zona pellucida, enabling the sperm to penetrate and fuse with the oocyte. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Zoology section), Chapter: Biology - Zoology portion covering relevant system and function.
Fertilization most commonly occurs in the fallopian tube, where the sperm meets the ovum. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Zoology section), Chapter: Biology - Zoology portion covering relevant system and function.
Fertilization usually takes place in the fallopian tube, where the sperm meets the ovum. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Zoology section), Chapter: Biology - Zoology portion covering relevant system and function.
During fertilization, maternal and paternal pronuclei must migrate centrally and meet before first mitosis for syngamy and diploidy. Sperm aster nucleated by centriole centrosome extends astral microtubules interacting with cortex. Dynein heavy chain DHC-1 with dynactin DNC-1, adaptor LIS-1, and nuclear envelope bridge SUN-1/ZYG-12 KASH drives minus-end directed pulling forces anchored at cortex. Cytoplasmic dynein reels pronuclei inward while pushing female pronucleus posteriorly. Kinesin KLP-18 opposes but dynein dominates net movement. Dynein inhibition via RNAi causes pronuclei to remain peripheral and asymmetric division failure.
Ref: Gonczy et al., Journal Cell Biology: Dynein-driven pronuclear migration and centrosome positioning in C. elegans zygote.
Upon C. elegans fertilization, oocyte and sperm pronuclei must migrate to meet. After sperm entry at posterior, sperm aster nucleates microtubules. Female pronucleus migration toward centrosome depends on minus-end directed motor dynein anchored on nuclear envelope via SUN-1, ZYG-12 LINC complex. Dynein pulls microtubules, drawing pronuclei together for fusion before first mitosis. Kinesin drives opposite plus-end movement, myosin actin provides cortical but not directed migration. Mutation in dhc-1 heavy chain or dnc mutants blocks pronuclear meeting, resulting in failed karyogamy and embryonic arrest, demonstrating dynein essential for pronuclear migration during fertilization.
Ref: Gonczy et al. 1999; WormBook: Dynein ensures proper nuclear migration during C. elegans fertilization.
Slow block stabilization requires chemical hardening making fertilization envelope resistant to proteases and mechanical penetration. Ovoperoxidase released from cortical granules uses hydrogen peroxide generated by NADPH oxidase to catalyze dityrosine crosslinks between tyrosine residues of vitelline envelope glycoproteins, increasing tensile strength. Transglutaminase subsequently introduces covalent epsilon-gamma-glutamyl-lysine isopeptide bonds further reinforcing matrix. Together enzymatic crosslinking converts soft elevated envelope into tough protective shell around early embryo. Glycosaminoglycans provide osmotic lifting force, hyalin forms inner hyaline layer supporting blastomeres adhesion, sodium influx drives electrical block but not envelope stabilization.
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Fertilization envelope stabilization by ovoperoxidase and transglutaminase crosslinking.
Phosphoinositide signaling during egg activation begins with hydrolysis of phosphatidylinositol 4,5-bisphosphate PIP2 residing in inner leaflet of plasma membrane. Enzyme catalyzing cleavage is phospholipase C activated via sperm-derived PLCzeta or Src kinase-mediated phosphorylation of PLCgamma after gamete fusion. Cleavage yields membrane-retained diacylglycerol activating protein kinase C and soluble inositol trisphosphate IP3 diffusing to endoplasmic reticulum triggering calcium release. Protein kinase C is downstream target not producer of IP3, dynein ATPase powers axonemal motility, Na+/H+ exchanger regulates pH independent of phosphoinositide turnover, making PLC sole generator of IP3 surge at fertilization.
Ref: NCBI Bookshelf, Cell Signaling, Chapter 9: Phospholipase C cleavage of PIP2 to generate IP3 and DAG.
Bindin represents classic example of rapidly evolving reproductive protein under positive selection driving speciation. It is insoluble acrosomal protein retained on acrosomal process after exocytosis, contacting vitelline envelope receptor EBR1. Sequence analysis reveals lectin domains mediating species-specific adhesion plus amphipathic helical regions destabilizing membranes promoting fusion, qualifying as fusogenic. It is not jelly component dissolving in seawater, not cortical granule enzyme released by egg, nor constituent of hardened fertilization envelope that consists of crosslinked vitelline glycoproteins. Its localization strictly on sperm ensures sperm side contributes adhesive and fusogenic activity essential for membrane merger and reproductive isolation.
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Bindin as sperm fusogenic and adhesive protein.
After sperm-egg plasma membrane fusion, egg cortex reorganizes beneath fusion site into funnel-like protrusion called fertilization cone that engulfs sperm head and midpiece drawing nucleus inward. This structure depends on rapid polymerization of cortical actin microfilaments orchestrated by small GTPases RhoA, Rac, and Arp2/3 complex nucleating branched filaments. Actin mesh pushes membrane around sperm and provides traction. Myosin II later contracts cone, tubulin microvilli elongate slightly, and dynein remains sperm flagellar motor. Inhibition of actin polymerization with cytochalasin D prevents cone formation leaving sperm attached externally, proving actin assembly essential for incorporation of male pronucleus.
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Fertilization cone formation via actin polymerization in egg cortex.
