1. 8- How cell divided
cell division 11
Meiosis; Reduction division
Dr. Siham Gritly
University of Bahri
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2. Meiosis; Reduction division
That Occurs in Sexually Reproducing
Organisms
• Part of the process of gamete formation,
• consisting of chromosome conjugation and two
cell divisions, in the course of which the diploid
chromosome number becomes reduced to the
haploid.
• Diploid cells have two homologous copies of each
chromosome.
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4. • Meiosis is used only for the production of
sperm and eggs
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5. Meiosis has two unique features: synapsis and
reduction division.
• 1- Synapsis
• * The process of pairing throughout the length
of the homologous chromosomes and
exchanging genetic fragments is called
synapsis.
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7. • 2-Reduction Division
• Reduction division: The first cell division in
meiosis, the process by which germ cells are
formed.
• In reduction division, the chromosome
number is reduced from diploid (46
chromosomes) to haploid (23 chromosomes)
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9. Meiosis features
• -yields genetically unique haploid daughter
cells (cells with only one member of each
homologous chromosome pair).
• -involves 2 nuclear and cytoplasmic divisions
• -produces 4 haploid cells
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10. The Sexual Life Cycle
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1. In the sexual life cycle,
there is an alternation of
diploid and haploid
generations.
2. Normal diploid body
cells are called somatic
cells.
3. Somatic cells arise
from the zygote and are
all genetically identical.

11. Germ-Line Tissues
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1. Cells that
produce gametes
are called germ-line
tissues.
2. Germ-line cells
will undergo
meiosis to produce
haploid gametes.

12. The stages of meiosis can be broken down into
two main stages, Meiosis I and Meiosis II
• A. Meiosis I can be broken down into four
substages:
• Prophase I,
• Metaphase I,
• Anaphase I
• and Telophase I
• Meiosis I serves to divide the two versions of
each chromosome;
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13. • B. Meiosis II can be broken down into four
substages:
• Prophase II,
• Metaphase II,
• Anaphase II
• and Telophase II
• meiosis II separates the two replicas of each
chromosome.
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14. Meiosis I
• The first cell division in Meiosis is known as
Meiosis I.
• The function of Meiosis I is very different
from that of either Mitosis or Meiosis II.
• In both Mitosis 1 and Meiosis II sister
chromatids are separated during anaphase
to produce identical daughter cells.
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16. • In Meiosis I members of homologous
chromosome pairs are separated.
• This results in the segregation of genes into the
two gametes.
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17. stages of Meiosis I :
• 1-prophase I occurs as the chromosomes
condense, homologues pair, and crossing over
occurs;
• Prophase; Main event in prophase of M1 is
“crossing over”, also called
“recombination”.
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18. • In crossing over, homologous chromosomes
pair up, and exchange segments by breaking
and rejoining at identical locations.
• ( Crossing over allows for combinations of
genes that may never have existed previously).
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19. Crossing over allows for combinations of genes
that may never have existed previously
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21. • 2-metaphase I involves formation of the
spindle apparatus and alignment of
chromosome pairs along the center of the cell;
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22. • 3-anaphase I, The centromeres break and
homologous chromosomes separate and pulled
toward the poles (note that the sister
chromatids are still attached)
• Cytokinesis begins
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23. • 4-telophase I, the chromosomes gather at each
pole and prepare for the second division.
• cleavage furrow formed
• Cytokinesis reaches completion, creating two
haploid daughter cells
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24. Meiosis II
• Meiosis II, which also has four stages, follows
after meiosis I,
• This result is the separation of the sister
chromatids to form four haploid gametes.
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25. 4 stages of meiosis11
• * prophase 11, the chromosomes condense
and the spindle forms.
• Centrioles form and move toward the poles
• The nuclear membrane dissolves
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26. • *Metaphase 11; chromosomes line up singly on the
cell equator.
• Microtubules grow from the centrioles and attach to
the centromeres
• The sister chromatids line up along the cell equator
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27. • *Anaphase 11; centromeres divide and pulled
to opposite poles.
• The centromeres break and sister chromatids
separate
• Cytokinesis begins
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28. • *telophase 11; cytoplasm divided into 2 cells.
• The chromosomes may decondense
• Cytokinesis reaches completion, creating four
haploid daughter cell
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29. Cytokinesis
• the cytoplasmic division of a cell at the end of
mitosis or meiosis, bringing about the separation
into two daughter cells.
• The division of the cytoplasm and the plasma
membrane following the division of the nucleus
resulting into two cells, each having its own
nucleus and cytoplasm surrounded by a plasma
membrane.
• This process begins during the late stage of
mitosis (Telophase) and meiosis (Telophase II).
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