What is cell division? Mitosis and its phases Meiosis and it's types

1. CELL DIVISION
MYTOSIS & MEIOSIS
(An assignment in Biology for Engineers)
Submitted by:
Ayush Agarwal
Submitted by:
Dr. Shashi Sharma

2. What is a Cell and Cell Division?
Cell is a basic building block of life! The cell divides into two, which
divides into four and so on to produce a living organism like us! Each
cell like us has a brain, called Nucleus. The nucleus holds and
protects the DNA which contains
information about a living organism
and because of which we are we!
Now, depending on whether a cell
has a nucleus or not, it becomes a
eukaryotic cell or a prokaryotic cell.
Cells with a nucleus are known as
Eukaryotic Cells while one without
a nucleus are known as Prokaryotic Cells. This assignment focuses on
Eukaryotes and Eukaryotic Cell Division.
Every cellular organism undergoes through the process of Cellular
Division, a process where parent cell breaks into two daughter cells
which performs the same operations as the parent cell. Cellular
Division keeps on occurring from while you are a zygote to when you
are hurt and a need to quickly fill the gap is required till you become
old and die.
There are 2 type of Cell division:
1. Mitosis
2. Meiosis
Mitosis
Mitosis is a process where a single cell divides into two identical
daughter cells. The Major purpose of Mitosis is for growth and to
replace worn out cells.
Figure 1 Eukaryotic and Prokaryotic Cell

3. If not corrected in time, mistakes made during cell division can result
in changed DNA, causing genetic disorders.
Figure 2 Stages of Mitosis
Mitosis is divided into five phases:
1. Interphase
Before the division of cell may start, the copy of genetic
material (DNA) has to be made. So, first the DNA in the cell is
copied which results in two identical full cells of
chromosomes.
2. Prophase
After the DNA is duplicated and condensed into
Chromosomes. Each chromosome is composed of two sister
chromatids, containing identical genetic information. They
pair up so that the copies of chromosome -1 and
chromosome -2 are together. At the end of Prophase,
Nucleus dissolves, leaving the DNA out in open to each cell.
Small string like objects called Spindle Fibers start to form
which extends across the cell.

4. 3. Metaphase
In metaphase, chromosomes line up in the middle of cell
with the help of spindle fibers. This is to organize
chromosomes before they gets divided in two cells.
4. Anaphase
The sister chromatids are pulled
apart by the mitotic spindle to the
opposite ends. This is the shortest
step of Cell Division.
5. Telophase
After chromosomes are in the two sides of the cell, the cell
begins to stretch. A new nucleus begins to form on either
side of cell containing the chromosomes. The cells then
breaks from the middle through cytokinesis, into two
daughter cells each containing a nucleus of its own.
Meiosis
Meiosis is a process where a single cell divides into two daughter
cells each containing half the genetic information of the parent cell.
This process is required to produce egg and sperm cells for sexual
Figure 3 Structure of chromosome during Anaphase

5. reproduction. The process takes the form of one DNA replication
followed by two successive nuclear and cell divisions (Meiosis I and
Meiosis II). Like Mitosis, Meiosis involves the first step i.e.
Interphase.
One cell in meiosis divides into twice to form four daughter cells
each containing half the number of chromosomes (haploid) the
parent cell (diploid).
Meiosis I
1. Interphase
This step is same as that of Mitosis which involves
duplication of genetic material to form two identical sets of
chromosomes.
2. Prophase I
Here is when the differences between
mitosis and meiosis starts to appear. As in
mitosis, the chromosomes condense to X
shaped structures that can be seen under
a microscope, but in meiosis I, they also
pair up. Each chromosome carefully aligns
with its homologue partner so that two
match up at corresponding positions
along their full length.

6. 3. Metaphase I
During Metaphase I, homologue pairs line up at
the center of the cell i.e. metaphase plate for
separation. When they line up at the
metaphase plate, the orientation is random
which allows formation of gametes with
different sets of homologues.
4. Anaphase I
The pair of chromosomes are then pulled apart
by meiotic spindle to opposite sides of the cell.
The sister chromatids of each chromosome
however, remains attached to one another and
don’t come apart.
5. Telophase I
In this step, the chromosomes complete their
movement to opposite poles of the cell. The
single cell is then split into two daughter cells
each containing a nucleus with full set of
chromosomes through cytokinesis.

7. Meiosis II
Meiosis I is followed by Meiosis II without copying their DNA.
Meiosis II is a shorter and simpler process and can be said as
“mitosis for haploid cells”.
Cells that will undergo Meiosis II are the ones in made in
Meiosis I, which are haploid and contain only one chromosome
but still consist of two sister chromatids.
6. Prophase II
During Prophase II, chromosomes in each of the two
daughter cells from Meiosis I condense into X shaped
Structures. Again, the centrosomes moves apart, the spindle
forms between them, and the spindle microtubules begin to
capture chromosomes again In both the daughter cells.
7. Metaphase II
In both daughter cells, the chromosomes line up end-to-end
along the equator of the cell. The centrioles again move to
opposite poles in both daughter cells and meiotic spindle
fiber at each pole attaches to each of the sister chromatids
in each daughter cell.
8. Anaphase II

8. The sister chromatids separate and are pulled to opposite
poles of the cell.
9. Telophase II
Nuclear membrane form around each set of chromosome to
create two nuclei. Each daughter cell then divides into two
of their daughter cells through cytokinesis resulting in four
haploid cells each containing half a set of chromosomes.
In humans, this results in sperm cells in males and egg cells
in females. In males all four cells are sperm cells and in
females, one of these four cells are egg cells while other
three are polar bodies (which does not develop into eggs).