Mitosis vs. Meiosis

Comprehensive Overview and Differences

Mitosis is a cell division process that results in two daughter cells. Each of those cells has the same number and kind of chromosomes as the parent nucleus. In other words, Mitosis is defined as a part of the cell cycle when replicated chromosomes are separated into two nuclei.

Mitosis vs. Meiosis

On
the other hand, meiosis involves the process of two successive cell divisions
and results in four daughter cells. Biologically, it is referred to as a
special type of cell division that reduces the number of chromosomes by half.
The process occurs in a sexually reproducing single-celled and multi cellular
eukaryotes.

Defining Meiosis – An Extensive Overview

The
concept of Meiosis is primarily based on the process where a single cell
divides twice in order to produce four cells. It contains half the original
amount of genetic information. These cells are also known as the sex cells;
eggs in females and sperms in males. Meiosis can be divided into 9 stages.
Here’s everything you should know about. Take a look.

Figure 1: The Stages of Meiosis

Meiosis Stage 1

1. Interphase

  • The DNA in the cell is copied; as a result two identical full sets of chromosomes are produced.
  • There are two centrosomes outside of the nucleus, each containing paired centrioles, considered crucial for the process of cell division.
  • Microtubules extend from these centrosomes during interphase. 

2. Interphase:

  • The DNA in the cell is copied; as a result two identical full sets of chromosomes are produced.
  • There are two centrosomes outside of the nucleus, each containing paired centrioles, considered crucial for the process of cell division.
  • Microtubules extend from these centrosomes during interphase. 

3. Prophase
I:

  • The copied chromosomes get condensed into X-shaped structures that are easily visible via microscopes.
  • Each chromosome is built with two sister chromatids that contain identical genetic information.
  • The chromosomes get paired up so that both copies of Chromosome 1 and 2 are together.
  • The pairs of chromosomes may then exchange small chunks of DNA in a process known as recombination or crossing over.
  • The membrane dissolves away at the end of the Prophase I, releasing the chromosomes.
  • The meiotic spindle that consists of microtubules and other proteins extends across the cell between the centrioles.

4. Metaphase I:

  • The pairs of chromosomes line up with each other along the centre or the equator of the cell.
  • The centrioles at the opposite polls will extend along with the meiotic spindle.
  • The meiotic spindles will now attach to one single chromosome of each pair.

5. Anaphase I:

  • The paired chromosomes are pulled apart by the meiotic spindle by pulling one chromosome to one pole and the other one to the opposite pole of the cell.
  • The sister chromatids in Meiosis I stay together, which is different from what occurs in Mitosis and Meiosis II.

6. Telophase I and Cytokinesis:

  • The chromosomes move to the opposite poles of the cells.
  • A full set of chromosomes gather at each pole of the cell.
  • A membrane is formed around each set of the chromosomes in order to produce two nuclei.
  • The single cell is pinched in the middle in order to form two separate daughter cells.
  • Each of them contains a full set of chromosomes within a nucleus. This process is known as Cytokinesis.

Meiosis Stage II

7. Prophase II:

  • There are two daughter
    cells, each having 23 chromosomes.
  • The chromosomes
    condense into visible X-shaped structures in each of the two daughter cells.
  • The membrane in each
    daughter cell dissolves away and releases the chromosomes.
  • The meiotic spindle is
    formed again as the centrioles duplicate.

8. Metaphase II:

  • The chromosomes in each
    of the two daughter cells line up end-to-end along the equator of the cell.
  • The centrioles are at
    the opposite poles in each of the daughter cells.
  • At each pole of the
    cell the meiotic spindle fibre attaches to each of the sister chromatids.

9. Anaphase II:

  • At this stage the
    sister chromatids are pulled to the opposite poles due to functionalities of
    the meiotic spindle.
  • The separated
    chromatids are individual chromosomes.

10. Telophase II and Cytokinesis:

  • The chromosomes shall
    now shift to the opposite poles of the cell.
  • A full set of
    chromosomes gather together at each pole of the cell.
  • Two new cell nuclei are
    created with the membrane forming around each set of chromosomes.
  • Another round of
    Cytokinesis completes the cell division.
  • There are four
    granddaughter cells, each with half a set of chromosomes.

Now that you are
aware of the meiosis definition and the different stages involved in the
process, let’s talk about the fundamentals of Mitosis.

Defining of Mitosis; A brief introduction

Mitosis
is the cell division where the mother cell divides in order to produce two new
daughter cells. These are genetically identical to one another. In this
particular part of the cell division process, the DNA of the cell’s nucleus is
divided into two equal sets of chromosomes. The majority of cell division that
happens in our body involves the process of Mitosis.

It
populates the organism’s body with cells. This particular process involves the
replacement of old, worn-out cells with the new ones.

Mitosis
consists of four basic stages; namely Prophase, Metaphase, Anaphase and
Telophase. Let’s delve deep into the fundamental aspects of each of the stages.

Figure 2: The 4 Stages of Mitosis

Stage 1: Prophase

Early Prophase: At
the stage of early prophasethe cell
tends to break down some structures and build up others. This, as a result,
sets the stage for division of the chromosomes. The chromosomes start to
condense and the mitotic spindle begins to form. Eventually, a part of the
nucleus where ribosomes are created disappears. This is an indication that the
nucleus is all set to break down.

Late Prophase:
Also known as the Prometaphase, the mitotic spindle starts capturing and
organising the chromosomes during the stage of Late Prophase.  The chromosomes are very compact as they
finish condensing, and the nuclear envelope breaks down, releasing the
chromosomes. Eventually, the mitotic spindle grows more with some of the
microtubules beginning to capture the chromosomes.

Stage 2: Metaphase

This is one crucial
phase where the spindle captures all the chromosomes and lines them up at the
middle of the cell. At this stage, all the chromosomes align at the metaphase
plate. The two kinetochores of each chromosome are attached to the
microtubules.

 Before advancing to the next stage of
Anaphase, the cell will check and make sure that all the chromosomes are at the
Metaphase plate with the kinetochores appropriately attached to the
microtubules.

Stage 3: Anaphase

At this
particular stage, the sister chromatids separate from each other. They are
eventually pulled towards the opposite ends of the cell. Here’s how the process
works. Take note.

  • The
    chromosomes of each pair are eventually pulled towards the opposite ends of
    each cell.
  • The
    microtubules that are not attached to the chromosomes will now elongate and
    push apart. This, as a result, will separate the poles and make the cells
    longer.

It is to be
noted that each of these processes is driven by motor proteins along the
microtubule tracks. The motor proteins in Mitosis carry other microtubules and
chromosomes as they walk.

Stage 4: Telophase 

As the cell in
Telophase is almost done dividing, it begins to re-establish its normal
structures as Cytokinesis occurs. Here’s how the entire process works.

  • The
    mitotic spindle is divided into building blocks.
  • Two
    nuclei are formed and the set of Nuclear membranes and Nucleoli reappears.
  • The
    chromosomes eventually begin to decondense as they return to their stringy
    forms.

Apart from knowing about the entire functionality of the different stages associated with the process of Mitosis, we shall also learn the difference between Mitosis and Meiosis.

How many cells are produced in mitosis?

There are
ideally two cells created after the process of Mitosis with the same 46
chromosomes. However, the Haploid cells are generated through Meiosis, for
example, egg and sperm having only 23 chromosomes.

Difference between Mitosis and Meiosis

When it comes to exploring the
various fundamental aspects associated with the study of Mitosis vs. Meiosis,
establishing well-defined points of difference between the two becomes crucial.
Here’s everything one must consider.

MITOSIS MEIOSIS
The type of reproduction involved in
Mitosis is asexual in nature.
The
type of reproduction involved in Meiosis is sexual in nature.
Mitosis is genetically similar. Meiosis
is genetically different.
There’s no scope for crossing over
to occur in Mitosis.
Meiosis
involves the process of mixing of chromosomes.
There is only one division. Meiosis
involves two divisions.
There is no pairing of homologs
involved.
Meiosis
involves the pairing of homologs.
The mother cells can either be
haploid or diploid.
The
mother cells are always diploid.
Two diploid cells are produced
during the process of Mitosis.
Four
haploid cells are produced during the process of Meiosis.
The number of chromosomes in Mitosis
remains the same.
The
number of chromosomes in Meiosis is reduced to half.
Chromosomes pairing do not occur in Mitosis. Chromosomes
pairing in Meiosis takes place during zygotene of the Prophase I up to
Metaphase I.
Creates everything apart from sex
cells.
Creates
female egg cells and male sex cells.
Mitosis takes place in somatic
cells.
Meiosis
takes place in germ cells.
The spindle fibre in Mitosis
disappears completely in telophase.
The
spindle fibre in Meiosis does not disappear fully in Telophase I.
Karyokinesis occurs in Telophase. Karyokinesis
occurs in Interphase I
The duration of prophase is short in
Mitosis. It is usually of a few hours.
The
duration of Prophase in Meiosis is relatively longer. It can take days to
complete.
The centomeres divide during the
stage of Anaphase.
The
Centomeres split during the stage of Anaphase I.

Table 1: Difference between Mitosis and Meiosis

Now that you know how is Meiosis different from Mitosis, take some time to recapitulate each of the points mentioned above for a firmer establishment of the entire concept. I hope the blog will add great values to your knowledge of Mitosis vs. Meiosis.

Good luck!

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