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Cell Reproduction
Mitosis & Meiosis
CELL DIVISION
allows organisms to grow, repair damaged
structures and reproduce
single-cell organisms: reproduce/make
more of their kind when one cell divides itself
multi-cell organisms: can reproduce when
special cells from two “parents” combine to
make a new cell
this new cell keeps dividing and a new
organism/living thing is formedver
CELL CYCLE
 when a cell grows,
prepares to be divided,
and then divides into
2 new “daughter” cells
 each “daughter” then
begins the cell cycle
again
 3 stages:
interphase, mitosis,
cytokinesis
Mitosis
• One type of cell division
Cell process in which the nucleus
divides to form two nuclei identical to
each other, and identical to the
original nucleus, in a series of steps
(prophase, metaphase, anaphase, and
telophase)
Mitosis allows for growth
and replaces worn out or
damaged cells.
Interphase
• Period of growth & development
• DNA replication (copied)
• Cells that do not divide (nerves)
are always in interphase
• Cells spend most of their time
here.
http://biotech-adventure.okstate.edu/low/basics/mitosis/phases/interphase/interphase.gif
Prophase
•DNA begins to shorten & thicken
–Now called chromatids /
chromosomes
•Centromeres form
•Nuclear membrane breaks apart
•Spindle fibers form
http://biotech-adventure.okstate.edu/low/basics/mitosis/phases/prophase/prophase.gif
Metaphase
•Chromatids / chromosomes
line up
•Centromere attaches to
spindle fibers
http://biotech-adventure.okstate.edu/low/basics/mitosis/phases/metaphase/metaphase.gif
Anaphase
•Centromeres divide
•Spindle fibers shorten
•Chromatid pairs separate – move
to ends of cell
•Chromatids are now called
–Each ½ of the pair is now called a
chromosome
http://biotech-adventure.okstate.edu/low/basics/mitosis/phases/anaphase/anaphase.gif
Telophase
•Spindle fibers disappear
•Chromosomes uncoil
•Nuclear membrane forms
•Cell divides (cytokinesis)
http://biotech-adventure.okstate.edu/low/basics/mitosis/phases/telophase/telophase.gif
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
http://biology.nebrwesleyan.edu/benham/mitosis/
Results of Mitosis
• Division of nucleus
–Nuclei are identical to each other
•Same number & type of chromosomes
Asexual Reproduction
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
Sexual Reproduction
Meiosis
Sexual Reproduction
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.
Sexual reproduction
results in a great variety,
or diversity, of offspring.
Meiosis
process of cell division where the
number of chromosomes is reduced
[made less] by half
chromosome pairs separate into 2
different cells, then divide again
(total of four cells)
chromosomes duplicate (make a
copy) before the first cell division
http://biotech-adventure.okstate.edu/low/basics/meiosis/diagram/
Interphase
• DNA is duplicated
Prophase I
• DNA shorten & thicken
– Forms chromatids / chromosomes
http://biotech-adventure.okstate.edu/low/basics/meiosis/phases/prophase/leptotene/leptotene.gif
Metaphase I
• Copied chromatids /
chromosomes line up in
middle of cell
• Centromeres attach to
spindle fibers
http://biotech-adventure.okstate.edu/low/basics/meiosis/phases/metaphase-I/metaphase-I.gif
Anaphase I
• Chromatid pairs are pulled
apart
–They DO NOT separate
• Move to ends of cell
http://biotech-adventure.okstate.edu/low/basics/meiosis/phases/anaphase-I/anaphase-i.gif
Telophase I
• 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. Both cells have
full sets of genetic
material
(chromosomes)
Prophase II
• Similar to mitosis
–Starts with TWO cells instead
of one
•Spindle fibers appear
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
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