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Meiosis
Group 3- Student 1, Student 2, Student 3, Student 4, Student 5,
Student 6
What is meiosis?
 Meiosis occurs in order to form gametes during
sexual reproduction in eukaryotes.
 Meiosis results in four genetically different, haploid
daughter cells from one diploid cell.
 While mitosis is completed by most types of cells
within an organism, meiosis is only completed by
the gonads, or reproductive organs within the
organism.
Phases of Meiosis:
 After DNA has replicated in the S phase of the cell life
cycle, Meiosis is completed in a series of phases similar
to mitosis, but meiosis has two divisions instead of one:
 Meiosis I




Prophase I
Metaphase I
Anaphase I
Telophase I & Cytokinesis
 Meiosis II




Prophase II
Metaphase II
Anaphase II
Telophase II & Cytokinesis
Meiosis I: Prophase I
 During Prophase I, DNA condenses into
chromosomes and becomes visible, crossing over
occurs, and the nuclear envelop disappears,
centrioles start to move toward the poles and the
meiotic spindle appears.
Crossing Over
https://www.youtube.com/watch?t=27&
v=5x_Rp1mwotQ
 Prophase I is important
because this is where
crossing over occurs
 Crossing Over results
in the genetic variation
of the four daughter
cells
 During crossing over,
parts of homologous
chromosomes may
break off and pair with
another set of
chromosomes
Meiosis I: Metaphase I
 During metaphase I, the
sister chromosomes line
up along the center of
the cell and spindle
fibers that extend from
the centrioles attach to
the centromere region of
the chromosomes.
Meiosis I: Anaphase I
 The spindle fibers
begin to shorten
and the cell
elongates as
microfilaments
push against each
other.
Chromosomes
move towards each
pole of the cell.
Meiosis I: Telophase I &
Cytokinesis
 During telophase I, the homologous chromosome pairs are
at either end of the cell and cytokinesis occurs.
 Cytokinesis is the process where a cleavage furrow forms,
pinching the cell into two daughter cells that are not identical
to the parent cell or to each other due to crossing over that
occurred.
 The two daughter cells only remain in this stage for a short
period before beginning Meiosis II.
Meiosis II: Prophase II
 Both of the two daughter cells from Meiosis I enter
Meiosis II starting with Prophase II.
 The sister chromatids condense and the meiotic
spindle appears.
 Crossing over does not occur during prophase II.
 Centrioles move towards the poles of the cell.
Meiosis II: Metaphase II
 The sister chromatids line
up along the center of the
cell and the spindle fibers
attach to the centromere
region of the
chromosomes.
Meiosis II: Anaphase II
 Spindle fibers shorten,
separating sister
chromatids and
moving chromosomes
to opposite poles of
the cell. The cell
elongates due to
microfilaments
pushing against each
other.
Meiosis II: Telophase II
and Cytokinesis
 During telophase II, the sister
chromatids are at opposite
ends of the cell. The nuclear
envelops form around the
chromatids at each end of the
cell and the cleavage furrow
begins to form.
 During cytokinesis, the
cleavage furrow pinches the
new cells in two.
The End Result:
 The completion of
meiosis results in four
haploid daughter cells
that are all genetically
different due to
genetic recombination
that occurs during
crossing over in
prophase I.
References
 http://www2.estrellamountain.edu/faculty/farabe
e/BIOBK/BioBookmeiosis.html
 http://www.aboutkidshealth.ca/en/howthebodyw
orks/geneticsintroduction/celldivision/meiosisintr
oduction/pages/stagesofmeiosisi.aspx
 All images were retrieved from Microsoft Clipart
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