Meiosis: Prophase 1 Video Lecture - NEET

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so let us quickly brief let me quickly
brief you about meiosis 1 and meiosis 2
so when we talk about meiosis 1 it is
reduction l division
why is it called induction l division
because two haploid cells are formed
from diploid cell so basically the
ploidy of the cell get reduced from
deployed to help life so it is reducing
that is why it is called reduction
division whereas when you talk about
meiosis 2 it is very similar to mitosis
it is an equation l division why because
here four haploid cells are formed from
two haploid cells so it is like haploid
2 employed so there is no change in the
ploidy of the cell so if it has n grow
set of chromosomes it still has n set of
chromosomes so here what happens so if
you look at the overall process of
meiosis what is happening one diploid
cell first forms two haploid cells then
these two applied cells form total four
haploid cells so this is the entire
process of meiosis so the first step is
reduction because the ploidy reduces
from deployed to employed the second
step is equation ax because both are
haploid so meiosis two will be very
similar to mitosis now we will talk
about each of the steps of first meiosis
1 and then meiosis 2 so let us talk
about profiles one of meiosis one so
what happens here so if you talk about
the proof if you try to compare it with
the prophase of mitosis you will see
that in the prophase one of meiosis one
is longer than mitosis longer than the
prophase of mitosis
so this prophase one is further divided
into many
that is it is divided into five stages
because the stage this prophase one is
quite complex and based on the behavior
of the chromosome during each phase of
the profiles monitor is divided into
five phases so the first stage stage is
left to teen what happens in this stage
the term left to teen it is derived from
the term left to lemma which means thin
threads so what happens at this stage
here the chromosomes gradually become
visible because before this the
chromosomes do not examine exist as such
they were all thread like chromatic
threads which were highly visible so
here the individual Kronos will start
and dancing and they start to become
compact so they tend to be visible they
are however they are very close to each
other they are so close that they are
almost indistinguishable from each other
they are so close so in this stage then
you clear em Philip on the nucleoli they
also disappear in fact the centrioles
also migrate to the opposite poles so
these are some of the things which
happen in this stage I mean this is a
very common which happens in any pro
fields now how does it look like let us
suppose if this is yourself so you
basically have two chromosomes like this
so let us suppose this is so both of
them are different why because we are
talking about sexual reproduction so why
is it received from the father the other
one is received from the mother so let
us suppose this is fattener that is
received from father and this is
maternal which is received from mother
so here the chromosomes become visible
at least and the nuclear membrane
nucleolus all those things disappear st.
rule's also move to migrate to opposite
poles somewhat like this the next stage
is
14 what is the meaning of Zico teen it
means paired threads so pairing will
take place in this stage right anyways
we I told you that meiosis is all about
pairing and recombination so that
pairing will happen in this is I go team
stage what happens here the homologous
chromosomes start pairing together
so water homologous chromosomes
homologous chromosomes are a set of
chromosomes which are like they both
belong to the same trait so how will the
homologous chromosome start pairing ah
something like this let us suppose this
is 1 over locus chromosome this is
neither moma locus chromosome
again so this is how they will pair up
right so this is one set of homologous
chromosome this is another set of
homologous chromosome because you have
chromosomes like this you have many
chromosomes like this so the homologous
chromosome will pair up so basically
this means that both of them.i two
copies of the same chromosome so this
process is known as synapses this is
called that is pairing of chromosomes
together is called synapses the third
stage is PAC heating the word Pakatan
means thick threads so you see that
Tooting with thin threads where you just
had individual chromosomes when they've
got period of favor called zygote in
which we meant paired threads now the
threads will be even thicker so what
happens here here bivalent chromosomes
appear as tech tracks so what does
tetrads now what will happen is that all
these so here you have two chromosomes
here you have two chromosomes now all
these four chromosomes will come
together like this so it became even
more thick and this
the word tech track means a group of
four a group of four that is called
tetra tetra means four so here if you
see one two three four so you have four
chromosomes grouped together and that is
why it is known as a tetrad so tetrad
formation takes place and packy team so
you see how thick it becomes that is why
it is named as packet in which means
thick threads so now here that this
stage now this tetrad is also known as
bi valent now in this stage there are
the sites where recombination takes
place new sites become visible and the
annual as recombination nodules let us
suppose let me try to draw it little
bigger something like this so if you see
these regions so these are the regions
that crossing over will take place
between this and this so crossing over
means exchange of genetic material
between the homologous chromosomes they
will say exchange genetic material that
is known as crossing over
so these recombination Manti wounds
become very very evident or they get
displayed at this stage that is packet
II so it is it is acquired along stage
longer than let doting and Zygo team
here recombination nodules appear as I
said and recombination occurs between
the homologous chromosomes
now what happens after recombination
then comes the dip low teen stage dip
low teen die means two so this means two
trends so now that they travel again
break into two parts that is why it is
called dip floating so dissolution of
the synaptic ml complex what is in act
animal is an actor named L is derived
from the term synapses as a result of
synapses that is pairing up a complex is
formed that is the structure of the food
chromosomes the tetrad that is known as
sin after never
complex so this will get dissolved so
what will happen chiasmata formation
will take place now let us see what is
chiasmata so here we will see later
suppose this is one chromosome this is
the second chromosome it is just a rough
picture now let us suppose this is the
third chromosome and this is the fourth
chromosome so now this is from say
maternal so this is a different
chromosome all together right so these
regions these regions are basically
egg-shaped regions because if you
actually see this is how it looks like
so these are X shaped regions if you see
here so this is how it actually looks
like so that X shaped region is quality
as matter which has already recombined
some properties so half of it will be
dark in colour for example it will be
something like this so this portion will
be dark in colour
the remaining portion will be white
whereas here this ocean will be dark in
color as remaining portion will be white
so that is how recombination will take
place and this egg shaped structure is
known as chiasmata and this is a very
long stage this stage can last even for
a couple of months so the recombined
homologous chromosome of the tetrad will
tend to separate from each other however
they will not get completely separated
so the egg shaped regions where they
will stay in touch that region is known
as chiasmata so chiasmata is the region
when crossing over had taken place so
recombination or you are those points
where the crossing over will take place
he has matter those regions where
crossing over have already taken place
and the last step is dying
Highness's what happens here dying
kindnesses kindnesses again is related
to kinetic that means movement so
Dionysus means moving true so here what
happens is terminal ization of chiasmata
so now it will completely break and it
will form two separate chromosomes so
something like this will be formed no so
this is one this is the second one so
the first one will look somewhat like
this because these are the regions where
the crossing over had taken place and
the second one will look somewhat like
this the second one was all red but now
if you see the regions of crossing over
they have slightly white so what do you
see this is your result
so the chiasmata is time analyzed that
means these regions have set apart from
each other but now you get two haploid
chromosomes right so this is not right
now you don't need to applied
chromosomes I'm sorry so here you get
two separate chromosomes where
recombination have taken place so now
none of them are exactly identical to
the paternal chromosome all exactly
identical to the maternal chromosome
both of them are a mixture of the two
so with this stage the prophase one ends
so here the chromosomes again get fully
condensed nucleolus disappears nuclear
membrane breaks down so all these things
happen which are form into profiles
nucleus will vanish nuclear membrane
will break down mitotic spindle will
begin to form that means the centrioles
will move towards opposite poles here
somewhat like this and then it will
start to form the spindle so now you
will find the process quite similar to
mitosis because the spindle formation is
taking place this step to present
transition to metaphase now as soon as
the spindle starts forming it indicates
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