Fertilisation

1. FERTILIZATION

2. FERTILISATION
It is the union of haploid male and
female pronuclei to form zygote
nucleus.
Or it is fusion of male and female
gametes to form zygote.
Usually it occurs in ampulla of
fallopian tube of female in human
beings.

3. STEPS BEFORE FERTILISATION
 Maturity of mates.
 Gametogenesis in mates.
 Copulation at proper time.
 Discharge of semen into female.
 Proper sperm count in semen.
 Proper shape, size & vigour in
sperms.

4. BEFORE FERTILISATION
 Both male and female mates must be
matured or attain puberty.
 Gametogenesis must occured in both.
 They must mate between 14th to 17th day
of menstrual cycle.
 Proper amount of semen must be
discharged into vagina by male. (2 to 4 ml
having 10 crore sperm per ml).
 60 % sperms should have proper shape,
size and structure and 40 % of them must
be vigourous.

5. STEPS OF FERTILISATION
 Attraction of sperm and secondary
oocyte
 Capacitation
 Penetration of sperm into corona
radiata
 Acrosome reaction
 Formation of fertilisation cone
 Resumption of meiosis – II of
oogenesis
 Migration of male pronucleus
 Amphimixis

6. STEPS OF FERTILISATION
 ATTRACTION OF GAMETES
 Secondary oocyte secrete a glycoprotein
named as FERTILIZIN.
 Sperm has an amino acidic receptor for
it named as ANTIFERTILIZIN.
 Antifertilizin is attracted towards
fertilizin and sperm move near egg.
 CAPACITATION
 Coating over sperm, mainly acrosome is
removed and it can accept signals of
fertilizin for movement towards it.

7. STEPS OF FERTILISATION
 PENETRATION OF SPERM
 After contact, sperm can enter corona
radiata and reach zona pellucida.
 ACROSOME REACTION
 At Zona pellucida, acrosome of sperm
breaks and release enzyme
HYALURONIDASE.
 It digests part of head zona pellucida
and vitelline membrane.

8. STEPS OF FERTILISATION
 FORMATION OF FERTILISATION CONE
 At point of contact to sperm, oolemma
forms a reception / fertilisation cone.
 After entry of first sperm, vitelline
membrane thickens and become the
fertilisation membrane that prevents
further sperm entry.
 Oolemma burst at cone, distal centriole
and nucleus of sperm enter into it. Entry
of centriole initiates second maturation
division forming ovum and secondary

9. STEPS OF FERTILISATION
 RESUMPTION OF MEIOSIS–II IN 2O OOCYTE
 Entry of distal centriole of sperm
initiates second maturation division in
secondary oocyte forming ovum and
secondary polar body.
 MIGRATION OF MALE PRONUCLEUS
 After entry, sperm nucleus enlarges to
become male pronucleus and ovum
nucleus become female pronucleus.
 Male pronucleus moves to female
pronucleus along penetration path.

10. STEPS OF FERTILISATION
 If female pronucleus is on same path, it
continue to meet on same path.
 If female pronucleus is not on same
path, it change path to copulation path.
 AMPHIMIXIS
 It is the union of haploid male and
female pronuclei forming deploid zygote
nucleus.
 This completes fertilisation.
 The mother is now said to be pregnant.

11. SIGNIFICANCE OF FERTILISATION
 It restores diploid chromosome number
in zygote from fusion of two haploid
gametes.
 It facilitates formation of ovum by
introducing centriole from sperm to
secondary oocyte.
 It forms first cell of all multicellular
bodies that is Zygote.
 Copulation path makes the axis of
cleavage in zygote.

12. PARTHENOGENESIS
 It is a special mode of sexual
reproduction in which, unfertilised egg
develops into embryo, without
contribution of male.
 Production of females by
parthenogenesis is THELYTOKY.
e. g. Aphid,
 Production of males by parthenogenesis
is ARRHENOTOKY.
e. g. Honey bee drone