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Cell Division: Mitosis and Meiosis

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Rhys Baker teaches science at Arthur Mellows Village College in Peterborough, UK.

Three types of cell division

Three types of cell division

Cell Division Glossary

Chromosome - A molecule of DNA wrapped around histones that becomes visible during prophase of cell division.

Chromatid - A replicated chromosome: each strand of the 'X' is a chromatid.

Diploid - Cells that have two copies of each chromosome in their nuclei.

Haploid - Cells that have one copy of each chromosome in their nuclei.

Homologous Chromosomes - Chromosomes that have the same genes in the same places. For each homologous pair, one comes from the mother, the other from the father.

What are the Stages of Mitosis and Meiosis?

All living things are made of cells - this is one of the key parts of Cell Theory. In order to survive, these cells must be able to make more cells. Cells achieve this using Cell Division - perhaps one of the more complicated topics I teach my A Level Biology students.

Cell division is the process by which biological cells multiply. There are three major types of cell division:

  1. Mitosis - used by Eukaryotic organisms to grow or reproduce asexually;
  2. Meiosis - used by Eukaryotic organisms to create sex cells (gametes);
  3. Binary Fission - used by Prokaryotic organisms to reproduce.

Despite their differences, remember that all three types of cell division begin with DNA replication - the act of doubling the amount of DNA in the cell.

Teaching Tip! The stages of cell division are complex and subtle. When examined on them, try to use labelled diagrams and tables to summarise the key information. Also ensure that all key terms are used appropriately, as this can save you time and energy.

Mitosis Stages

Mitosis is the process of cell division that forms two genetically identical nuclei from on parent cell nucleus. It is used for:

  • Asexual reproduction (e.g. Paramecium)
  • Growth (increasing cell number)
  • Repair and Maintenance (replace damaged cells with identical replacements)

Although we traditionally break down mitosis into a series of stages and sub-stages, it is actually a continuous process. In the micrographs opposite, you can see that mitosis is not necessarily synchronised and looks much messier than the clean, idealised textbook diagrams!

Interphase - Not strictly a stage of mitosis, this is where the cell prepares to divide by growing, storing energy, replicating organelles and replicating DNA.

Prophase - The chromosomes supercoil and become visible under a light microscope. The chromosomes assume their classic 'X' shape - two sister chromatids joined in the middle at the centromere. Other key events are:

  • Nuclear Envelope breaks down;
  • Centriole divides in two, travels to opposite poles of the cell to form the spindle.

Metaphase - An easy stage to identify, Metaphase is characterised by the chromosomes lining up, single file, along the middle (the equator) of the cell. At this point, each chromosome becomes attached to the spindle at its' centromere.

Anaphase - Another easily recognisable stage! Anaphase sees the chromosomes split at the centromere, separating the sister chromatids:

  • The sister chromatids are pulled apart to opposite poles of the cell
  • At this point, each chromatid becomes an individual chromosome - identical to the original parent chromosome
  • Spindle fibres shorten, pulling each chromatid by the centromere - this causes the chromatids to look like Vs

Telophase - a simple stage to recognise - you will see two nuclei starting to form in early telophase; in late telophase you will no longer be able to see the chromosomes, just two complete nuclei at opposite ends of the cell.

Interphase, Prophase, Metaphase, Anaphase and Telophase

StageMain EventKeyword

Interphase

DNA is replicated, Cell builds up energy reseves and grows.

Increase

Prophase

DNA Packaged - the chromosomes shorten and thicken

Packaging

Metaphase

Chromosomes line up in the middle of the cell

Middle

Anaphase

Chromatids break apart at the centromere and move to opposite poles

Apart

Telophase

Two nuclei formed after nuclear envelopes reform around each group of chromosomes

Two (nuclei)

Summary of Mitosis

The Stages of Meiosis

Meiosis Stages

Human body cells have 46 chromosomes. These are arranged in pairs, with one copy of each chromosome from Mum, and the other from Dad. If your sperm and eggs were made using mitosis, when these two cells fused at fertilisation, the egg would have 96 chromosomes. Definitely not human!

Meiosis is the process of cell division that halves the chromosome number and makes gametes (human gametes contain 23 chromosomes). This ensures that at fertilisation the number of chromosomes found in normal body cells - the diploid number - is restored.

Meiosis involves two divisions of the nucleus:

  • The first division generates most of the variation
  • The second division halves the chromosome number.

Meiosis is a very technical process that is most easily described in diagrams and tables (see above and below).

A human Karyotype image.

A human Karyotype image.

What are Homologous Chromosomes?

In the photo to the right, you can see all the chromosomes from a human cell. In the inset box, you see all of the chromosomes paired up according to size - this is called a karyotype. Each pair is known as a homologous pair. In each pair, one chromosome comes from Mum and the other comes from Dad.

Homologous chromosomes are:

  • The same size;
  • The same shape;
  • Have the centromere in the same place;
  • Have the same genes.

The X and Y chromosomes have only one small region that is homologous, but are still grouped together as they determine the sex of an individual.

During Crossing over, analogous sections of DNA from homologous chromosomes are swapped over.

During Crossing over, analogous sections of DNA from homologous chromosomes are swapped over.

What is Crossing Over?

Crossing over (and recombination) is where homologous chromosomes exchange genetic material and create 'recombinant chromosomes.'

During Prophase I, homologous chromosomes line up with each other and swap small amounts of their DNA from similar regions. Without recombination and crossing over, all alleles on a single chromosome would be inherited together. This system creates new gene combinations which increases our capacity (as a species) to respond to environmental change.

Meiosis Summary

StageKey Event

Prophase I

Chromosomes condense, Crossing over occurs

Metaphase I

Homologous chromosomes pair up and align in middle of cell

Anaphase I

Homologous chromosomes pulled apart

Telophase I

Nuclear Envelope reforms

Cytokinesis I

Cell splits into two

Prophase II

Centrioles divide and move to opposite poles

Metaphase II

Chromosomes attach to spindle fibres and line up along equator

Anaphase II

Sister chromatids break apart at centromere and migrate to opposite poles

Telophase II

Nuclei reform, Chromosomes uncoil

Summary of Meiosis

Cell Division Resources

Comparison of Mitosis and Meiosis

 MitosisMeiosis

Number of daughter cells made

2

4

Are the daughter cells identical

Yes

No

Number of nuclear divisions?

1

2

Haploid or Diploid?

Diploid

Haploid

Where does this occur?

Body Cells

Gonads

Do homologous chromosomes pair up?

No

Yes

Function

Growth and Asexual Reproduction

To make sex cells (gametes)

Crash Course in Meiosis

The above video analyses meiosis in great detail. It also has links to videos on related topics. This is a fantastic revision resource that all of my students are required to watch.

Cell Division Quiz

For each question, choose the best answer. The answer key is below.

Answer Key

Interpreting Your Score

If you got 0 correct answers: Cell Division Aborted! Go back and take a closer look at the information. Start with the videos and tables!

Cell Division Links

  • Cell Division Animations
    Excellent animations showing the stages of mitosis, meiosis and many more key biological processes. (Select using the drop-down menu in the top left corner)
  • Meiosis Tutorial
    A series of illustrations showing the stages of meiosis. Complete with knowledge check. Suitable for Degree level students (similar pages exist for mitosis)
  • Mitosis: An Interactive Animation
    Interactive animation showing the stages of animal cell mitosis.

© 2013 Rhys Baker

Comments

bernard on November 18, 2019:

captivating and good one indeed, very interesting

Sami khan on October 15, 2019:

Diagram are not clear and

Rumbidzai Machibiza on September 10, 2019:

clearly explained wow

sneha on September 07, 2019:

amazing thanks alot for the help

manimekala on May 27, 2019:

clear explanation

Ishaq zailani galadima on April 07, 2019:

Very nice explanation. Thank you

Ishaq zailani galadima on April 06, 2019:

Add Your Comment.my comment is how genetics is calculate

Bharti Daduriya on January 17, 2019:

Very nice explanation

Abhideep prajapati on November 30, 2018:

Good and but also improvement in explanation .

Princess on November 09, 2018:

Not good

Shaik Nishat on November 02, 2018:

Nice explanation ☺️

alexbeen on October 31, 2018:

I've always tried to make comparison charts in everything I can, this made things so easier. I hope you could make more side by side comparisons like this http://ask4essay.com/difference-between-mitosis-an...

Samreen qureshi on September 16, 2018:

Very good explanation about mitosis and meiosis .

very well deserved

Rishav kar on July 12, 2018:

actual state ments that i needed

billy bob joe on May 31, 2018:

this was not what i wanted

ajeet singh on March 11, 2018:

very nice explanation about this topic.

nicomp really from Ohio, USA on May 31, 2015:

The first instance of Mitosis and the first instance of Meiosis must have been wildly successful. They are pass-fail processes, survival-wise.

Horatio Plot from Bedfordshire, England. on June 05, 2013:

I only read this because it was you. I was fully prepared to be bored to death, but guess what; I rather enjoyed it. You have the knack of making something dry go all moist and juicy; the sign of a great teacher and communicator. Congrats on HOTD. Hubscribers on a roll!

Abdus Salam from Bangladesh on June 04, 2013:

Congratulations! your hub on hub of the day. Great hub. thanks for sharing...

Robie Benve from Ohio on June 04, 2013:

Excellent hub! A well deserved HOD. Full of interesting info and great graphics.

rose-the planner from Toronto, Ontario-Canada on June 04, 2013:

Fascinating! Excellent and insightful article. Thank you for sharing and congratulations on HOTD. (Voted Up) -Rose

Sid Kemp from Boca Raton, Florida (near Miami and Palm Beach) on June 04, 2013:

This is an excellent hub. I did learn this in high school 40 years ago, and I think everyone should know it. Your presentation skills are extraordinary! I hope to come back and read about binary fission. Will you be writing about that?

whonunuwho from United States on June 04, 2013:

These key biological processes are something that all high school students should be aware of. Those who wish to go further in the science field and biological study are well benefited by this early study. Thanks for sharing this very interesting work. whonu

summerberrie on June 04, 2013:

Congrats on HOTD!

Marcy Goodfleisch from Planet Earth on June 04, 2013:

What an amazing hub! It's like a mini chapter in biology, and excellent.presented so that it's understandable and interesting to follow! I have a question - would one of these processes be the way identical twins are created? Mitosis sounded the closest to it, to me.

Congratulations on the HOTD! Voted up and sharing!

Lucy Jones from Scandinavia on June 04, 2013:

It's mind boggling - but a very interesting topic and one I'm sure many can benefit by. Thanks for taking the time to share. Voted up and shared.

Rumana from Sharjah, UAE on June 04, 2013:

You have given very brief information.......

Maricar M. Jolo from Jubail, Kingdom of Saudi Arabia on June 04, 2013:

Very informative! Congrats! :D

Yvonne Spence from UK on June 04, 2013:

Congrats on your HOTD, well deserved!

torrilynn on March 23, 2013:

this will be very beneficial to me when i take Biology again

also its really does help to tell the difference between the two

thanks and Voted up

Robie Benve from Ohio on February 03, 2013:

Great informative hub! Voted up and awesome! :)

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