All life has to begin somewhere. In fact
you and I or let's say humans we all
have started our life from a single cell.
This single cell is what we call a
zygote. Now the zygote is formed by the
fusion of a male and a female
reproductive cells or the gametes. So
due to the fusion of these gametes a zygote is formed
and this fusion is what
you call fertilization. So let's see
fertilization in detail. So do you know
that during sexual reproduction the male
deposits the sperm in the female
reproductive tract? Now these sperms in
the female reproductive tract they float
to the oviduct or the fallopian tube. Now
here in the fallopian tube they may
find an ova released from the ovary
but there's something very important for
you to note that out of those millions
sperms only a single sperm can mate the
ova to fertilize it to produce a baby. The
rest of the sperms they usually die. So
as a first step of reproduction now this
ova and sperm will meet and this meeting
of sperm and ova will result in the
formation of a single cell and this
meeting or the fusion of these two
gametes is what we call a fertilization.
So we can simply call fertilization as
the fusion of male and a female nuclei
to form a single nucleus and the
cell which is formed by the male and
female gametes this cell is known as a
zygote. So zygote it is the first
cell of a new life and this zygote it
contains the chromosomes from both the
mother and the father and as it
contains the chromosome from both
mother and father the baby which is
going to develop from this zygote will
have the characteristics of both mother
and the father. So you can also note this
in yourself as well so I’m sure you have
realized that some of your characters it
matches with your mom and some of your
characters they match with your father.
Right now if you see in here this
process of fertilization it is taking
place inside a female reproductive
system. So when it is taking place inside
the female reproductive system we can
call this process as internal
Fertilization. So internal fertilization
is a type of fertilization which occurs
inside the female reproductive system. It
can be seen in various animals such as
in human cat, cow, dog, hen etc. On the
other hand you will be surprised to know
that there is a different kind of
fertilization. In this type of
fertilization the male and the female
gametes they fuse together outside the
female body. Now when it is occurring
outside the female body it can also be
called as external fertilization. This
type of fertilization it is usually seen
in the aquatic animals such as in frogs,
fishes etc. Now let us take an example of
frogs to understand external
fertilization. Frogs move to the water
bodies like pond during the rainy season.
Now when the male and female frog they come
close they come together. The female frog
it lays hundreds of eggs. Are you
thinking that this female it is
going to give birth to hundred babies?
Well no. Some of these eggs they get
eaten up by other animals. So that is the
need why she lays hundreds of eggs. Now next
the laid eggs, the eggs which are laid by
this female they get covered with the
delicate with a very thin layer of a
jelly. This jelly it protects these eggs up
to some extent and it also keeps them
together. Now the male frog it deposits
the sperm over these laid eggs. As you
know the sperm floats you know with the
help of its tail, these sperms of the Frog
also they float randomly over these eggs
and when these sperms they come in
contact with the eggs the fertilization
may take place. Now such type of
fertilization is what we call external
fertilization. So external fertilization can
be simply defined as a type of
fertilization which occurs outside the
female body. So now you have understood
that the fusion of male and a female
gamete it can occur either inside or
outside the body. Next let us see
something more interesting. Do you know
in some women the fallopian tube is
blocked due to some reason? Now these
women they cannot bear babies as you
know the sperm cannot reach the ova to
fertilize it. So how does the
fertilization take place in such women?
Well in such cases the eggs from the
female reproductive system are collected
with the help of a syringe and similarly
the sperms from the male are collected
in a test tube. Now these egg and sperm
are allowed to fuse in this test tube
to form zygotes. So, usually the ratio of
you know this ratio it is in the
proportion of one egg is to 75,000 sperms.
Now the zygotes which are formed by the
fusion of these two are allowed to
develop for a week or so and the healthy
zygotes from this developed ones,
they are placed back in the
mother's uterus.
Now these zygotes they develop like in a
usual way to form babies and such babies
are known as test-tube babies and this
kind of fertilization which has just now
occurred in the test tube is what you
call in vitro fertilization. So we can
simply say that in vitro fertilization
or IVF it is a type of fertilization
which occurs in a test tube and such
babies which develop through the in
vitro fertilization are known as
test-tube babies. So we have just now
seen how a mother who is not you know
reproductively well how she can go under
the IVF. You know there is a big
misconception that the test tube babies
they are developed completely in the
test tube only but the fact is that only
the fertilization takes place in the
test tube and the rest of the
development as you have just seen it
occurs inside the mother's uterus. So
students in this lesson now you have
understood that what is fertilization. So
we have just seen that fertilization is
nothing but the fusion of male and
female nuclei to form a single nucleus.
You have also seen that fertilization it
is usually of two types where an
internal fertilization is a type of
fertilization which occurs inside the
female reproductive system
and the external fertilization on the
other hand it occurs outside the female
reproductive system. You have also seen
that test tube babies are the babies
which develop from the in vitro
fertilization i.e., from the
fertilization in the test tubes.
