Meiosis is a process of cell division that results in four haploid daughter cells each with half the number of chromosomes as the original diploid parent cell. It includes one round of DNA replication followed by two divisions, meiosis I and meiosis II. In meiosis I, homologous chromosomes pair and may exchange genetic material through crossing over, then separate so that each daughter cell receives one chromosome of each pair. Meiosis II separates sister chromatids, resulting in four haploid daughter cells that are genetically different from each other and the parent cell. Meiosis produces gametes for sexual reproduction.

1. Meiosis..
Edited By:
Gift Thamsanqa Lubisi (201209380)

2. Introduction..
• A process of reduction division in which the number of
chromosomes per cell is cut in half through the
separation of homologous chromosomes in a diploid cell.
• Diploid – 2 sets of chromosomes.
It is the term used to refer to a cell that
contains both sets of homologous chromosomes.
• Haploid – 1 set of chromosomes.
it is the term used to refer to a cell that
contains only a single set of chromosomes.

3. Meiosis
• Sex cells divide to produce gametes
(sperm or egg).
• Gametes have half the # of chromosomes.
• Occurs only in gonads (testes or
ovaries).
Male: spermatogenesis
Female: oogenesis
• Meiosis is similar to mitosis with some
chromosomal differences.

4. Homologous chromosome….
Homologous - term used to refer to chromosomes that
each have a corresponding chromosome from the
opposite-sex parent.
Homologous chromosomes are similar in shape, position
and information, but not identical to each other.

5. Homologous chromosome.

6. Important definitions..
• Meiosis is a process of reduction division in which the
number of chromosomes per cell is cut in half through
the separation of homologous chromosomes in a diploid
cell.
• Tetrad - structure containing 4 chromatids that forms
during meiosis.
• crossing-over - process in which homologous
chromosomes exchange portions of their chromatids
during meiosis

7. Crossing over..

8. Crossing over..
• Formation of a tetrad while going through the process of
crossing-over
• This occurs during prophase I of meiosis.

9. Introduction..
• Meiosis have mainly two division..
Meiosis-I.
Meiosis-II.

10. Interphase I
Phases of Meiosis
Copyright Pearson Prentice Hall
Cells undergo a round of DNA
replication, forming duplicate
chromosomes.

11. Copyright Pearson Prentice Hall
MEIOSIS I
Phases of Meiosis
Prophase I
Each chromosome pairs with its
corresponding homologous
chromosome to form a tetrad.
There are 4 chromatids in a tetrad.

12. Crossing Over - variation
nonsister chromatids
chiasmata: site
of crossing over
Tetrad
variation

13. Copyright Pearson Prentice Hall
Synapsis
and
Crossing
Over in
Action

14. Phases of Meiosis
MEIOSIS I
Metaphase I
Copyright Pearson Prentice Hall
Spindle fibers attach to the
chromosomes.
Tetrads line up in the middle:
metaphase plate.

15. Spindle fibers pull the
homologous chromosomes
toward opposite ends of the
cell.
Tetrads split into single
chromosomes.
MEIOSIS I
Anaphase I
Copyright Pearson Prentice Hall
Phases of Meiosis

16. Nuclear membranes form.
Cell separates into two cells.
The two cells produced have
chromosomes and alleles that are
different from each other and from
the diploid cell that entered meiosis
I.
MEIOSIS I
Telophase I and
Cytokinesis
Copyright Pearson Prentice Hall
Phases of Meiosis

17. Phases of Meiosis
The two cells produced by meiosis I now enter a second meiotic
division.
Unlike meiosis I, neither cell goes through chromosome
replication.
Each of the cell’s chromosomes has 2 chromatids.
Copyright Pearson Prentice Hall
Meiosis II

18. Telophase-1..

19. Meiosis-II
• No interphase..
• Similar to Mitosis…

20. Prophase-II..
• Cells have one set of sister chromatids
• Nuclear membrane breaks down
• Centrioles separate.
• Each of the daughter cells forms a spindle,
and the double stranded
chromosomes moves towards
the equator..

21. Metaphase-II..
• Sister chromatids line up at the middle of the
cell..

22. Anaphase-II..
• The centromeres of sister chromatids finally
separate.
• The sister chromatids of each pair
move toward opposite poles.
Now its individual chromosomes.

23. Telophase-II..
• Cells start to split in two
• Each cell has one set of chromosomes—it is a haploid
• Nuclei form at opposite
poles of the cell and
cytokinesis occurs.
• After completion of
cytokinesis there are
four daughter cells.
• All are haploid (n)..

25. Common non disjunction
disorder..
•
•
•
•
Down’s Syndrome – Trisomy 21
Turner’s Syndrome – Monosomy 23 (X)
Kleinfelter’s Syndrome – Trisomy 23 (XXY)
Edward’s Syndrome – Trisomy 18

26. A Comparison of Mitosis and Meiosis
• Mitosis conserves the number of chromosome
sets, producing cells that are genetically
identical to the parent cell
• Meiosis reduces the number of chromosomes
sets from two (diploid) to one
(haploid), producing cells that differ genetically
from each other and from the parent cell
• The mechanism for separating sister
chromatids is virtually identical in meiosis II and
mitosis
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

27. Fig. 13-9
MITOSIS
MEIOSIS
Parent cell
Chromosome
replication
Prophase
Chiasma
Chromosome
replication
Prophase I
Homologous
chromosome
pair
2n = 6
Replicated chromosome
MEIOSIS I
Metaphase
Metaphase I
Anaphase
Telophase
Anaphase I
Telophase I
Haploid
n=3
Daughter
cells of
meiosis I
2n
MEIOSIS II
2n
Daughter cells
of mitosis
n
n
n
n
Daughter cells of meiosis II
SUMMARY
Property
Mitosis
Meiosis
DNA
replication
Occurs during interphase before
mitosis begins
Occurs during interphase before meiosis I begins
Number of
divisions
One, including prophase, metaphase,
anahase, and telophase
Two, each including prophase, metaphase, anaphase, and
telophase
Synapsis of
homologous
chromosomes
Does not occur
Occurs during prophase I along with crossing over
between nonsister chromatids; resulting chiasmata
hold pairs together due to sister chromatid cohesion
Number of
daughter cells
and genetic
composition
Two, each diploid (2n) and genetically
identical to the parent cell
Four, each haploid (n), containing half as many chromosomes
as the parent cell; genetically different from the parent
cell and from each other
Role in the
animal body
Enables multicellular adult to arise from
zygote; produces cells for growth, repair,
and, in some species, asexual reproduction
Produces gametes; reduces number of chromosomes by half
and introduces genetic variability amoung the gametes

28. Fig. 13-9a
MITOSIS
MEIOSIS
Parent cell
Chromosome
replication
Prophase
Chiasma
Chromosome
replication
Prophase I
Homologous
chromosome
pair
2n = 6
Replicated chromosome
MEIOSIS I
Metaphase
Metaphase I
Anaphase
Telophase
Anaphase I
Telophase I
Haploid
n=3
Daughter
cells of
meiosis I
2n
Daughter cells
of mitosis
2n
MEIOSIS II
n
n
n
n
Daughter cells of meiosis II

30. Reference list:
• Gretchen, G. (2012). Meiosis slideshare. Available from:
http://www.slideshare.net/gunthergretchen/biologa-meiosis [Accessed 06 March 2014].
• Guest21d4fb. (2010). Meiosis slideshare. Available from:
http://www.slideshare.net/guest21d4fb/meiosis-2 [Accessed 06 March 2014].
• Patel, S. (2013). Meiosis slideshare. Available from:
http://www.slideshare.net/GIFTTHAMSANQA1663/savedfiles?s_title=meiosis28422102&user_login=Lionheart009 [Accessed 06 March 2014].
• Swan, J. (2011). Meiosis slideshare. Available
from: http://www.slideshare.net/jayswan/chapter-13-presentation-6504581 [Accessed 06
March 2014].