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Developmental
assignment

Register no: 17BTYE007
Name: N
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07
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Akshaya
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U
Dr
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C

Biology

Contents​:
introduction
1)occurrnce of fertilization
2)After the process of ovulation
3)process of fertilization
4)History of sperm
5)History of egg
6)Morphology of sperm
7)Morphology of egg
8)Recognition of egg and sperm
9)sperm attraction-Action at a distance 10)The
acrosomal reaction in sea urchin
11)Species-specific recognition in sea urchins:
12)Induction of mammalian acrosomal
13)secondary binding of sperm to the zone pellucida
14)Diseases
15)conclusion
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Introduction about Fertilization:

"The process of combining the male gamete or
sperm with the female gamete or ovum
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The two cells unite during
fertilization, they form a diploid cell
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When sperm enters the vagina during sexual
intercourse, these sperms swim through the cervix
and uterus and finally in to the Fallopian tube
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Only one
sperm penetrates in to the egg and finally breaks
throughout the cell membrane of the egg
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2)After the process of ovulation :
After the sperm penetrates the egg,its tail falls
off
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The resulting zygote contains all the
chromosomes needed for a new individual
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The stages of fertilization can be divided into four
process
*Sperm preparation
*Sperm egg recognition and binding
*Sperm-egg fusion
*Fusion of sperm and egg pronuclei and
activation of the zygote
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Preparation of the Sperm
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In response to the
dilution of semen in the vagina, they undergo several
changes, which are collectively known as
capacitation​
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Intracellular Ca++ levels increase
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Spermatic motility is activated and tails change
beat frequency
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Sperm cell surface antigens are lost
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Step II
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In sea urchins, the
sperm head binds directly to the egg outer surface
and this triggers the acrosome reaction
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The increased pH
triggers the dissociation of the profilactin complex
(actin and profilin) and the released actin monomers
polymerize to form a filament called the acrosomal
process
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In sea urchins then, the sperm
literally skewers the egg
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STEP III
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For many years the process by which the plasma
membrane of the sperm and egg fused was a black
box
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Judith White, Diana Miles, and Paul
Primakoff and their colleagues, have now shed light
on this process
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This suggested that ​PH-30 was involved in
sperm and egg fusion and it was given the name
fertilin
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Activation - The Egg’s Response
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Polyspermy
refers to the fertilization of the egg by more than one
sperm, resulting in zygotes with greater than a

diploid amount of DNA
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3)Process of fertilization :
During fertilization the sperm burrow through the
egg shell(zona pellucida) to reach the outer
membrane of the egg
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Once the
sperm penetrates the egg, a reaction occurs that
hardens the egg membrane to prevent the entry of
other sperms
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After the egg drops from the ovary, it travels through
the Fallopian tube, it stays there for 24hours so it
can be fertilized
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It was discovered by
Anton van leeuwenhoek, the Dutch micropist in
1678
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Later he believed that each sperm
contains a performed embryo
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Leeuwenhoek was
disappointed in his inability to find the performed
embryo within the spermatozoa
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Nicolas hartsoekar, co-discover of sperm,
drew a performed human("homnculus") within the
sperm
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Many investigators

considered spermatozoa is an unimportant and as
an enormous waste of time
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L
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B
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They noted
that it is universally existed in all sexually matured
males and they are absent in immature and aged
individuals
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Von Kolliker describe the formation of
sperm from cross of adult testes
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In 1876, Oscar hertwig and
Herman For demonstrated the entry of sperm into
the egg and those cells nuclei
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Hertwig repeatedly
observed a sperm entering an egg and saw the two
nuclei unite after mixing the both together and he
noted that one sperm enters the egg and all the
nuclei of the embryo derived from the fused nucleus
after fertilization
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Fertilization was at last recognized as
the union of sperm and egg and the gametes of sea
urchin remains the best example
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Karl Ernst von Baer discovered
the mammalian ovum in 1827, and Edgar Allen
discovered the human ovum in 1928
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6)Morphology of sperm:
Each sperm consist of a haploid nucleus, a
propulsion system to move the nucleus and has a
sac of enzymes to enable the nucleus to enter the
egg
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During the
maturation of the sperm, the haploid nucleus
becomes very streamlined and it's DNA becomes
slightly compressed, in front of the haploid nucleus

acrosomal vesicle is present
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It is
considered to be lysosome
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The awesome
and nucleus constitute the head of the sperm
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flagella are complex structure
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7)Morphology of egg​:
The materials that is necessary for the
beginning of growth and development must be
stored in the mature egg(the ovum)
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It either
absorbs or synthesizes proteins such as yolk, they
act as a food source of developing embryo
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The egg
cell, or ovum (plural ova), is the female reproductive
cell (gamete) in oogamous organisms
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When egg and sperm fuse, a
diploid cell (the zygote) is formed, which rapidly
grows into a new organism
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The chemoattraction of the sperm to the egg by
soluble molecules secreted by the egg
2
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The binding of the sperm to the extracellular
envelope (vitelline layer or zona pellucida) of the egg
4
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Fusion of egg and sperm cell plasma membranes
9)Sperm attraction: Action at a distance:
Species-specific sperm attraction has been
documented in numerous species, including
cnidarians, molluscs, echinoderms, and
urochordates
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In 1978, Miller demonstrated that the eggs of
the cnidarian ​Orthopyxis caliculata​ not only secrete a
chemotactic factor but also regulate the timing of its
release
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Miller found that when sperm were added
to oocytes that had not yet completed their second
meiotic division, there was no attraction of sperm to
eggs
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Thus,
these oocytes control not only the type of sperm they
attract, but also the time at which they attract them
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In most marine
invertebrates, the acrosomal reaction has two
components:

the fusion of the acrosomal vesicle with the sperm
plasma membrane (an exocytosis that results in the
release of the contents of the acrosomal vesicle) and
the extension of the acrosomal process
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Contact with
egg jelly causes the exocytosis of the sperm’s
acrosomal vesicle and the release of proteolytic
enzymes that can digest a path through the jelly coat
to the egg surface
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A major
species-specific recognition step occurs at this point
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In 1977, Vacquier and co-workers
isolated this nonsoluble 30,500-Da protein from the
acrosome of ​Strongylocentrotus purpuratus​ and
found it to be capable of binding to dejellied eggs of
the same species
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purpuratus​ binds to its own dejellied

eggs, but not to those of ​Arbacia punctulata
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This crosslinking opens calcium
channels to increase the concentration of calcium in
the sperm
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The

calcium channels in the membrane would be
sensitive to this change in membrane potential,
allowing calcium to enter the sperm
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In the sea urchin, the vitelline envelope is
very thin and porous
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In mammals, however, the
zona pellucida is a very thick matrix, so the sperm is
far removed from the egg
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Indeed, sperm that undergo
the acrosomal reaction before they reach the zona
pellucida are unable to penetrate it
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This region is where the ​ZP3​-binding
proteins are located, and yet the sperm must still
remain bound to the zona in order to lyse a path
through it
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​ Whereas acrosome-intact sperm will not bind to
ZP2,​ acrosome-reacted sperm will
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The structure of the zona
consists of repeating units of ​ZP3​ and ​ZP2​,
occasionally crosslinked by ​ZP1​ (Figure 7
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It
appears that the acrosome-reacted sperm transfer
their binding from ​ZP3​ to the adjacent ​ZP2
molecules
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One of the proteins released by these granules is a
protease that specifically alters ​ZP2​
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In guinea pigs, secondary binding to the zona is
thought to be mediated by the protein PH-20
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The blood sera of these sterile guinea pigs
had extremely high concentrations of antibodies to
PH-20
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The
contraceptive effect lasted several months, after
which fertility was restored
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14)Diseases​:
Various disorders can arise from defects in the
fertilization process
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However, some researchers have found that in rare

pairs of fraternal twins, their origin might have been
from the fertilization of one egg cell from the mother
and eight sperm cells from the father
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15)Conclusion​:
we will consider how fertilized eggs
prevent additional sperm from fusing (a condition
known as polyspermy) and how the fertilized egg is
activated to begin development
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ncbi
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nih
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ck12
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Scott F
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