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Cellular Division
Mitosis
Meiosis
Chromosomes
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Humans have 23 pairs
of chromosomes
1 set inherited from
mother
1 set inherited from
father
https://bioinformatics.cs.vt.edu/~heath/IMAGES/human_chromosomes.gif
Chromosome
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DNA is called chromatin
when in cell during
normal functioning of
cell – cannot discern
anything except
nucleolus
DNA replicates
When cell divides, DNA
condenses into tight “X”
shape, one side the
original and the other
side copied DNA
http://www.yorku.ca/kdenning/images/bioanthropology/chromosome.jpg
Mitosis – Somatic Line

Mitosis
http://staff.kings.edu/kdils/StudentWork/Kalinay%20Lessons/lesson_plan_3_files/image007.jpg
Mitosis Stages - Interphase

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Cell spends most of its
life in interphase (G1)
Signaled to replicate
DNA (S phase)
Cell resumes normal
functions with
replicated DNA (G2)
http://kvhs.nbed.nb.ca/gallant/biology/mitosis_phases.jpg
Mitosis Stages - Prophase
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DNA condenses
Spindles form (they
organize and guide
DNA as it separates to
each side of the cell
Nucleus begins to
dissolve
Spindle fibers attach
DNA
http://kvhs.nbed.nb.ca/gallant/biology/mitosis_phases.jpg
Mitosis Stages - Metaphase

DNA lines up
along equator
of cell
http://kvhs.nbed.nb.ca/gallant/biology/mitosis_phases.jpg
Mitosis Stages - Anaphase

Spindle fibers
attached to DNA
shorten and DNA
moves to one side of
the cell
 Notice that arms
of the
chromosome
separate
http://kvhs.nbed.nb.ca/gallant/biology/mitosis_phases.jpg
Mitosis Stages - Telophase

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Cell begins to pinch in
along the equator of the
cell
Nucleus begins to form
Mitosis
http://kvhs.nbed.nb.ca/gallant/biology/mitosis_phases.jpg
Mitosis Stages – Interphase – 2 cells

Cell spends most of
its life in interphase
(G1)

Signaled to replicate
DNA (S phase)

Cell resumes normal
functions with
replicated DNA (G2)
http://kvhs.nbed.nb.ca/gallant/biology/mitosis_phases.jpg
Meiosis – Germ Line

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Sexual Reproduction
In humans – 23 pairs of
chromosomes, or a
total of 46
chromosomes

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1 chromosome from
mother
1 chromosome from
father
Meiosis
Meiosis
http://www.accessexcellence.org/RC/VL/GG/meiosis.php
Meiosis Stages - Interphase



Cell spends most of
its life in interphase
(G1)
Signaled to replicate
DNA (S phase)
Cell resumes normal
functions with
replicated DNA (G2)
http://www.dnaletters.com/img/3.gif
http://www.realscienceprograms.com/files/IMAGES/egg_cell.jpg
Meiosis Stages – Prophase I
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DNA condenses
Replicated DNA from
adjoining chromosomes
crossover
Spindles form (they
organize and guide DNA as
it separates to each side of
the cell
Nucleus begins to dissolve
Spindle fibers attach DNA
http://scienceprofonline.googlepages.com/meiosis.jpg/meiosis-full.jpg
http://www.ri.net/schools/Narragansett/NHS/mywebpage/meiosis.jpg
Meiosis Stages - Metaphase I

Replicated
chromosomes of DNA
lines up along equator
of cell
http://scienceprofonline.googlepages.com/meiosis.jpg/meiosis-full.jpg
http://www.ri.net/schools/Narragansett/NHS/mywebpage/meiosis.jpg
Meiosis Stages - Anaphase I
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Spindle fibers attached
to chromosome DNA
shorten and one of the
pairs of chromosome of
DNA moves to one side
of the cell – or the other
Chromosome number
in humans – 23 – no
longer in pairs
http://scienceprofonline.googlepages.com/meiosis.jpg/meiosis-full.jpg
http://www.ri.net/schools/Narragansett/NHS/mywebpage/meiosis.jpg
Meiosis Stages – Telophase I
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Cell begins to pinch in
along the equator of the
cell
Division not yet
complete
NOTE – cells now only
have half the
chromosome number
http://scienceprofonline.googlepages.com/meiosis.jpg/meiosis-full.jpg
http://www.ri.net/schools/Narragansett/NHS/mywebpage/meiosis.jpg
Meiosis Stages - Prophase II

Spindle fibers form and
attach to DNA
http://scienceprofonline.googlepages.com/meiosis.jpg/meiosis-full.jpg
http://www.ri.net/schools/Narragansett/NHS/mywebpage/meiosis.jpg
Meiosis Stages - Metaphase II

DNA lines up along
equator of cell
http://scienceprofonline.googlepages.com/meiosis.jpg/meiosis-full.jpg
http://www.ri.net/schools/Narragansett/NHS/mywebpage/meiosis.jpg
Meiosis Stages - Anaphase II

Spindle fibers
attached to DNA
shorten and DNA
moves to one side of
the cell
 Notice that arms
of the
chromosome
separate
http://scienceprofonline.googlepages.com/meiosis.jpg/meiosis-full.jpg
http://www.ri.net/schools/Narragansett/NHS/mywebpage/meiosis.jpg
Meiosis Stages - Telophase II


Cells begins to pinch in
along the equator of the
cell
Nucleus begins to form
http://scienceprofonline.googlepages.com/meiosis.jpg/meiosis-full.jpg
http://www.ri.net/schools/Narragansett/NHS/mywebpage/meiosis.jpg
Meiosis Stages – Interphase – 4 cells

Cell spends most of
its life in interphase
(G1)

Signaled to replicate
DNA (S phase)

Cell resumes normal
functions with
replicated DNA (G2)
http://scienceprofonline.googlepages.com/meiosis.jpg/meiosis-full.jpg
http://www.ri.net/schools/Narragansett/NHS/mywebpage/meiosis.jpg
Fertilization (Humans)
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Egg with 23
chromosomes
Sperm with 23
chromosomes
Fertilization – zygote
with 23 PAIR of
chromosomes!
TA DA! (Sea Urchins)
http://www.brown.edu/Courses/BI0032/gentherp/pronucl.jpg
Questions?
BJ Shaw Panochthus frenzelianus American Museum of Natural History 2004