Biology

3. Interphase:
Nuclear envelope
still there
And its before S
phase because the
centrioles arent
duplicated yet

4. The chromatin
condensed
together to create
visible
chromosomes.

5. The spindle fibers
also begin to form
Migration of the two
pairs of the centrioles
to the opposite sides
of the cell.
Thinning and gradual
disappearance of
nuclear envelope.

6. Gradual mixing of
the nucleolus with
the rest of the
nucleus.
The nuclear
envelope is almost
completely
disappeared

7. Metaphase is marked by
the alignment of all the
chromosomes at the
equatorial plane of the cell
(the metaphase plate).
The nuclear membrane
dissolves
completely, marking the
beginning of metaphase.
Attachment of the the
spindle fibers to the
centromere of the
chromosome at a point
called kinetochore.

8. Movements of the
chromosomes
occurs due to
shortening of
spindle
microtubules and
kinetochore
movement along
the spindle fibers.

9. Migration and
arrival of the new
chromosomes to
the opposite poles
of the cell.

10. During this
stage, daughter
chromosomes arrive at
opposite poles of cell
and the spindle fibers
disappear.
The chromosomes
change into
chromatin and
become invisible
under the light
microscope.
Nuclear envelope
begins to form around
the new nuclei.

11. Cytokinesis or
cleavage of the
cytoplasm of the
cell begins.

12. myosin molecular motors
attach to the actin and draw
the membrane in -like a
purse string.
Once the sister chromatids
are separated, a ring of actin
filaments (microfilaments)
form a
“contractile ring”around
the middle of the cell
By the end of telophase,
two independent
daughter cells have been
formed

14. Interphase: “ before
Sphase”
1. the nuclear
envelope still there
2. the chromosomes
aren't condensed
yet
3. Replication of
centrioles didn’t
occur

15. Interphase: “ after S
phase”
1. the nuclear
envelope still there
2. the chromosomes
started to condense
3. Replication of
centrioles took
place

16. Early prophase 1:
The chromatin condensed
together to create visible
chromosomes.
The spindle fibers also
begin to form at this time.
And centrioles begun to
move away from each
other
The maternal and paternal
homologous chromosomes
come close to each other
and then align
Disappearance of the
nuclear envelope is
happening gradually

17. Prophase 1:
Same as the previous
slide except that The
two homologous
chromosome now
consists of four
chromatids, so these
chromosomes are
called TETRAD.
And now they are
connected at the
chiasma

18. Late prophase 1:
Crossing over takes
place between the
tetrad at the
Chiasma *crossing
over of segments of
chromatids*

19. Metaphase1:
The homologous paired
chromosomes are shown to
be connected by a terminal
chiasma and arranged in the
equatorial plate.
The mitotic spindle fibers
connect the centromere of
each chromosome on one
side and the pole of the
dividing cell on the other side
Attachment of the the spindle
fibers to the centromere of the
chromosome at a point called
kinetochore.
Nuclear envelope is
disappearing

20. The terminal chiasma
disappears and the
chromosomes become free
from each other.
The centromere remains
undivided so sister chromatids
move together to the
opposite poles of the cell.
This movement occurs due to
shortening of spindle
microtubules and kinetochore
movement along the spindle
fibers.
Migration and arrival of the
new chromosomes to the
opposite poles of the cell.
Imp: here seperation of the
chiasma takes place but NO
division of centromere so the
sister chromatids don’t
separate here

21. During this
stage, cytokinesis
occurres by
contraction of actin
filaments around the
center of the cell
which gives two
daughter cells.
The chromosomes
become thinner and
then changed to
chromatin.
The nuclear envelope
reforms and the
nucleolus reappears

22. The two daughter cells
that resulted from the
1st meiotic division
have 23 (1n)
chromosomes and (2C)
DNA.
These cells pass in a
short interphase called
interkinesis during
which duplication of
centrioles occurs but no
replication to DNA takes
place (NO S Phase).
Check in the next slide
we have two yellow
structure which is the
centrioles so before we
start meiosis 2
centrioles must be
duplicated

23. › no further
replication occurs
› chromosomes line
up again
(metaphase II)
› sister chromatids
separate (telophase
II and anaphase II)
› the cells divide and
chromosomes
decondense
(cytokinesis, teloph
ase II)

24. Four haploid cells *
gamete cells* in
which 2 are parental
, and 2 are
recombinant due to
crossing over

25. Wish you the best of luck and inshallah we
will all do good in the exams and pass and
get HIGH grades =)
You are the best future
dentists <3