Transcript Cell Reproduction

Mitosis & Meiosis
Cell Cycle
 G1 (Gap 1)- cells carry out
normal metabolic activities
for day to day functions.
 S (Synthesis)- DNA is
replicated (duplicated,
copied).
 G2 (Gap 2)- cell prepares for
cell division by doubling cell
organelles.
Mitosis
 A stage of the cell cycle that involves the division of the
nucleus into two new nuclei that contain identical
copies of the genetic information.
 Mitosis is divided into 4 stages based on the cellular
events: Prophase, Metaphase, Anaphase, Telophase.
(PMAT)
 If you include Interphase (IPMAT – I phoned mom and
talked)
Functions of Mitosis
1. Growth
2. Repair regenerate damaged tissues.
3. Regeneration of entire body parts simpler organisms.
4. Maintenance of the body.
Mitosis and cytokinesis occur in our body cells (aka
somatic cells)
Interphase
 Period of growth & development
 Hereditary information (DNA)
copied (replicated / duplicated)
 Cells that do not divide (nerves)
are always in interphase
Prophase
DNA begins to shorten & thicken
Now called chromatids/chromosomes
Centromeres form
Nuclear membrane breaks apart
Spindle fibers begin to form
Metaphase
Chromatids / chromosomes
line up
Centromere attaches to
spindle fibers
Anaphase
Centromeres divide
Spindle fibers shorten
Sister chromatid pairs separate –
move to opposite ends of the cell.
Telophase
Spindle fibers begin to disappear
Chromosomes begin to uncoil
Nuclear membrane starts to re-form
Cell plate (plant cell) or Cleavage
furrow (animal cell) becomes highly
noticeable.
Cytokinesis (Cell Cutting)
 The division of the cytoplasm is know as cell cutting.
This signals the end of Mitosis.
 After the cells membrane or wall forms a complete new
barrier between the two sister cells. We would say
cytokinesis has just occurred.
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
http://biology.nebrwesleyan.edu/benham/mitosis/
Mitosis Animation
http://www.johnkyrk.com/mitosis.html
Results of Mitosis
 Division of nucleus
 Nuclei are identical to each other

Same number & type of chromosomes
A type of reproduction - fission,
budding, and regeneration - in
which a new organism is produced
from one parent and has DNA
identical to the parent organism.
Asexual Reproduction
Offspring produced from one
organism
Hereditary information is
identical
Mitosis is one form of asexual
reproduction
Meiosis
A type of reproduction in which
two sex cells, usually an egg and
a sperm, join to form a zygote,
which will develop into a new
organism with a unique identity.
Meiosis
 The nucleus divides twice
 Meiosis I
 Meiosis II
 Final Product will be 4 cells from one parent
that contains ½ the original amount of
chromosomes as the parent.
Interphase
 Same as in Mitosis.
 Normal life cycle functions of the cell
 Divided into 3 stages:
 G1 (Gap 1)- Growth and development
 S (Synthesis Phase) - DNA is duplicated
 G2 (Gap 2)- Organelles double in preparation
for separation
Prophase I
DNA begins to shorten & thicken
Now called chromatids/chromosomes
Centromeres form
Nuclear membrane breaks apart
Spindle fibers begin to form
 CROSSING OVER may occur.
Metaphase I
Copied chromatids /
chromosomes line up in
middle of cell in
HOMOLOGOUS PAIRS
Centromeres attach to spindle
fibers
Anaphase I
 Homologous chromosomes
separate and move to the poles.
Chromatid pairs are NOT
pulled apart
 They DO NOT separate
Chromatids move to ends of
cell
http://biotech-adventure.okstate.edu/low/basics/meiosis/phases/anaphase-I/anaphase-i.gif
Telophase I
May or May Not occur.
 If it does:
 Normal telophase, X-somes
uncoil, nucleus appears, cell
divides
No further replication of
hereditary material
http://biotech-adventure.okstate.edu/low/basics/meiosis/phases/telophase-I/telophase-I.gif
- There are now two cells with each
cell carrying only ½ the original
chromosome number. (HAPLOID)
- Cells carry one duplicated copy of a
single chromosome.
 They do not normally or necessarily carry the
same genetic information as the parent cell
or the sister chromatid.
 Because the chromosome number decreases
this phase of meiosis is known as
Reduction Division.
Prophase II
Similar to mitosis
 Starts with TWO cells instead of
one
Spindle fibers appear
 Nucleus disappears (if reformed)

http://biotech-adventure.okstate.edu/low/basics/meiosis/phases/prophase-II/prophase-II.gif
Metaphase II
Duplicated chromatid /
chromosomes line up in
middle of cell
Spindle fibers attach to
centromeres
http://biotech-adventure.okstate.edu/low/basics/meiosis/phases/metaphase-II/metaphase-II.gif
Anaphase II
Centromere divides
 Chromatids separate & move to
ends of cell

Chromatids are now individual
chromosomes
http://biotech-adventure.okstate.edu/low/basics/meiosis/phases/anaphase-II/anaphase-II.gif
Telophase II
Spindle fibers disappear
Nuclear membranes form at
each end of cell
Cells divide
 Results in 4 cells

Each with ½ the original number
of chromosomes
http://biotech-adventure.okstate.edu/low/basics/meiosis/phases/telophase-II/telophase-II.gif
http://www.johnkyrk.com/meiosis.html
In summary:
Meiosis
 Two cells form during meiosis I
 In meiosis II, both of these cells form two
cells
 The two divisions of the nucleus result in four
sex cells (gametes)
 Each has one-half the number of
chromosomes in its nucleus that was in the
original nucleus