Fertilization
Animal Breeding
Pensacola Jr College
Sperm Maturation
w In the epididymis:
• Gain motility
• Gain fertility
• Lose cytoplasmic droplet
w In female reproductive
tract:
• Final maturation process
Capacitation
w Second sperm maturation
process in the female reproductive tract before they are capable of
fertilization
w Binding of GAG molecules (glycosaminoglycans),
a sugar
Capacitation
GAG binding
w Chemicals in seminal fluid
prevent GAG binding, so they must be diluted in female tract
w Heparin is often the GAG
molecule
w Functions of GAG binding:
• Increased sperm motility
• Stimulates calcium influx
GAG Binding
Increased Motility
Acrosome Reaction
w Calcium influx causes sperm
cell membrane to fuse with outer acrosomal membrane
w Allows release of acrosomal
enzymes
w Enzymes allow breakdown of
egg coatings
Acrosome Reaction
Acrosome Reaction
Acrosomal Enzymes
w Hyaluronidase à breaks down cumulus
w Corona-penetrating enzyme à breaks down corona
w Acrosin à breaks down zona pellucida
Fertilization
w Penetration of egg by sperm
and fusion of egg and sperm nuclei to form diploid zygote
w Process:
• Zona Reaction
• Vitelline Block
• Nuclei Fuse
Step 1 – Zona
Reaction
w Sperm has penetrated zona
using acrosin
w Sperm cell membrane fuses
with egg cell membrane
w Cortical granules fuse with
egg cell membrane
w Enzymes of cortical granules
cause zona to harden so no more sperm can enter zona
Zona Reaction 1
Zona Reaction 2
Zona Reaction 3
Step 2 – Vitelline
Block
w First sperm that has fused
to egg cell membrane has head taken in, tail and midpeice degenerate
w Fusion of cortical granules
and other factors prevent more sperm cells from fusing to egg cell membrane
Vitelline Block
Step 3 – Nuclei
Fuse
w Engulfing of sperm head
reinitiates meiosis (completion from metaphase II and extrusion of 2nd
polar body
w Sperm and egg haploid nuclei
fuse
w Zygote (diploid) is formed
Sperm and Egg
Pronuclei
Pronuclei Fuse
Polyspermy
w Fertilization by more than
one sperm cell
w In this case zygote will
have more than 2n chromosome #
w Usually results in embryo
death
w Occasionally has led to new
species (3n of old species)
Prevention of
Polyspermy
w Normally prevented by zona
reaction and vitelline block
w Breakdown of system:
• Aged oocytes (older female
animals)
• High temperatures (during
fever etc)