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Asexual Reproduction
Mitosis
Mitosis is the process in which
the nucleus divides to form two
new nuclei.
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How do little elephants grow up to be big
elephants?
Why do animals shed their skin?
The process of asexual
reproduction begins after a
sperm fertilizes an egg.
Three reasons why cells reproduce
by asexual reproduction:
1. Growth
2. Repair
3. Replacement
Skin cancer - the abnormal growth of
skin cells - most often develops on skin
exposed to the sun.
Cell that reproduce by asexual
reproduction reproduce constantly.
Mitosis
• All daughter cells contain the same genetic
information from the original parent cell from
which it was copied
• Every different type cell in your body
contains the same genes, but each cell only
“reads” a certain portion of the genome
• This serves to make the cells specialized,
such as into nerve or muscle tissue
Animated Mitosis Cycle
http://www.cellsalive.com/mitosis.htm
• Interphase
• Prophase
• Metaphase
• Anaphase
• Telophase & Cytokinesis
Chromosomes
Interphase
occurs before mitosis begins
- Chromosomes are copied (# doubles)
- Chromosomes appear as threadlike coils (chromatin) at
the start, but each chromosome and its copy(sister
chromosome) change to sister chromatids at end of this
phase (they are packaged up)
Nucleus
CELL
MEMBRANE
Cytoplasm
Interphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Prophase
1st step in Mitosis
- Mitosis begins (cell begins to divide)
- Centrioles (or poles) appear and begin to move to
opposite end of the cell.
- Spindle fibers form between the poles.
Centrioles
Sister chromatids
Spindle fibers
Prophase
Animal Cell
Plant Cell
Spindle fibers
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Metaphase
2nd step in Mitosis
- Chromatids (or pairs of chromosomes) attach to the
spindle fibers.
- These chromosomes line up along the center of the
cell
Centrioles
Spindle fibers
Metaphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Anaphase
3rd step in Mitosis
- Chromatids (or pairs of chromosomes) separate and
begin to move to opposite ends of the cell.
Centrioles
Spindle fibers
Anaphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Telophase
4th step in Mitosis
- Two new nuclei form.
- Chromosomes unspool and appear as chromatin
(threads rather than packages rods).
- Mitosis ends.
Nuclei
Chromatin
Nuclei
Telophase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Cytokinesis
occurs after mitosis
- Cell membrane moves inward to create two
daughter cells – each with its own nucleus with
identical chromosomes.
Animal Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Plant Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Cell Cycle
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Mitosis
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Mitosis Animation
http://www.cellsalive.com/mitosis.htm
• Interphase (90% of cycle)
•
G1 phase
– Time for cell to be a cell
– Can become G0 phase in nerve,
muscle and other cells
•
S phase
– synthesis of DNA
• G2 phase
– Time for cell to be a cell
• Mitotic phase
– Mitosis in stages
The True
Cell Cycle
Life Span of a Cell
• A cell only has a
limited amount of
cycles “coded”
into it
• Caused by
telomeres
• “Fixed” by
telomerase
Cancer
• Tumor (mass of cells)
– Benign
• Relatively harmless
– Malignant
• Puts itself at the top of the cell importance hierarchy
• Metastasis
– Spreading of cancerous cells/tissue
Mitosis Practice Quiz
• Use two words to describe the importance of
mitosis
• Draw and label the cell cycle…include
Interphase, Prophase, Metaphase, Anaphase,
Telophase, and Cytokinesis…what happens at
each stage?
• Why might telomerase be important?
• What disease is associated with mitosis?
• Are all organisms limited to a certain number of
mitotic divisions? In other words, are there any
organisms which can be effectively “immortal”