Fertilization fro the graduation Students

process of fertilization in animals

5. FERTILIZATION

6. INRODUCTION
The union of sperm nucleus of paternal origin with an egg nucleus
of maternal origin to form the primary nucleus of the embryo.
It is Second important event in sexual reproduction.
Also called as Syngamy.
The process was discovered by Leeuwenhock in 1683.
Fertilization in frog’s egg: George Newport (1854)
Fertilization in sea urchin: Oscar Hertwig (1875)
This process has two independent function
1.Activation
2.Amphimixis

7. Types of Fertilization
Source of
Gametes
Place and nature of
fluid medium for
movement of sperms
Number of sperm
entering into ovum
Nature of fusing
Gametes
External
Internal
Cross
fertilization
/exogamy
Self
fertilization
/Endogamy
Anisogamy
Isogamy
Polyspermy
Monospermy
Marine
FW
Protandrous
Protogynous
PathologicalPhysiological

8. Species Specificity in Fertilization
It is important because it maintains the individuality of the
species.
Achieved with the help of certain Chemical substances.
Fertilizin : Gycoprotein composed of different aa and
monosaccharides in different species. Secreted by Egg
Anti Fertilizin : present on the surface of sperm.
composed of acidic amino acid.
Theses chemical cause Agglutination reaction. First reported by
F. R. Lillie.

9. PROCESS OR MECHANISM
Steps involved
1.Approximation of male and female gamete
2.Entry of Spermatozoon into ovum
3.Fusion of Sperm and Egg
4.Fusion of Sperm and Egg nucleus

10. STEP1: Approximation of male and
female gametes
Viability of gamete:
Occurs by two different ways:
External
Internal
Two phenomenon:
1.Activation of sperm motility
2.Attraction of sperms to the egg

11. Activation of sperm motility
In sea urchin it is controlled by intracellular pH.
Semen (high CO2 conc)
Sea water (Low CO2, High pH :8.0)
•Respiration
•Motility
Respiration
Flagellar movement starts

12. Role of egg to provide motility to sperm
Jelly coat
(sperm activating peptide
called SPERACT)
Egg
Sea water (Low CO2,
High pH :8.0)
Respiration
Flagellar
movement starts
Activation
of dynein

13. Attraction of sperm to the Egg
Chemotaxis: Chemical attraction
Because now we need direction

15. STEP 2: Entry of Spermatozoon into ovum
Two events
1. Sperm Capacitation
2. Acrosomal reaction

16. CAPACITATION

19. ACROSOMAL REACTION
Mammals
Sea urchin

21. Acrosomal reaction in mammals
Lysins
Hyaluronidase
Corona penetrating enzyme

22. 3 Fusion of Sperm and Egg
Plasma membranes Fusion of both the gametes and form
cytoplasmic bridge
In sea urchin: tip joins
In mammals: Equatorial region
Usually entire sperm enter.
Fertilization /reception cone:

25. PREVENTION OF POLYSREMY
MONOSPERMY: entry of one sperm leads to
POLYSPERMY: entry of more than one sperm
Physiological Polyspermy: hen’s Egg
Equal genetic
distribution
Restoration of diploidy
Polyploidy
Death

26. Prevention
Many mechanism:
Fish egg: multiple entry of sperm is restricted by micropyle
in the chorion
Egg coat acts as barrier
Mammals: long distance to reach the egg
Degeneration of extra male pronucleus.
The polyspermy checked at the level of surface by two
methods in sea urchin:
1.Fast block polyspermy (temporary)
2.Slow block polyspermy (permament)

32. Slow block polyspermy
Mechanical process
 Cortical reaction: mechanism involved exocytosis
Cortical grannule serine protease
Mucopolysacharides
Fertilization membrane
Peroxidase enzyme

33. FUSION OF SPERM AND EGG
NUCLEUS
10-20 mint
Sea urchin
Formation of pronuclei
Female pronucleus (centre of egg)
Male pronucleus (cortex of egg)
Formation of sperm ester: microtubules
centriols
Synkaryon

34. Mammals
approximation

35. Significance
Restore the diploidy
Introduce variation
Stimulate egg to complete its maturation
Activate the ovum
Introduce the centriols
Prevent polyspermy
Determine the sex
Rearrangement of various organ forming substances
Makes egg more active metabolically.