Download CELL REPRODUCTION

CELL
REPRODUCTION
Kimberly Lozano
Biology 490
Spring 2010
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CELL CYCLE
Interphase
G1: Growth (1)
New organelles form
within the cell.
S: Synthesis
Cell duplicates its DNA.
G2: Growth (2)
Cell prepares for
division to take place
during the mitotic
phase.
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Mitotic
M phase
Mitosis. Chromosomes
divide.
Cytokinesis.
Cytoplasm and cell
membrane divide.
Chromosomes as Packaged
Genes
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DNA double helix bound to
histones
DNA wrapped around histones
form nucleosome
Further coiling of nucleosome
produce 30nm wide chromatin
fiber
Coiling of chromatin fiber
produce “x” shaped
chromosome
Chromosome consists of two
identical sister chromatids
joined at the centromere
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Prokaryotic Chromosome
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Single circular chromosome
Plasmids
What is Mitosis?
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Mitosis produces two daughter cells that are identical to the parent cell.
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If the parent cell is haploid (N), then the daughter cells will be haploid.
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If the parent cell is diploid, the daughter cells will also be diploid.
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N
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This type of cell division allows multicellular organisms to grow and repair damaged
tissue.
centrioles
N
2N
2N
Interphase
•Chromatin is condensing into chromosomes and centrioles
have duplicated in preparation for mitosis.
• Chromosomes are not visible because they are uncoiled
nuclear envelope
Chromatin
Prophase
•Duplicated chromosomes are visible.
•Centrioles begin moving apart.
•Nuclear envelope is fragmenting and will disappear.
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Metaphase
• The spindle fully develops and the
chromosomes align at the metaphase
plate
Anaphase
• Chromosomes are pulled along the
microtubules toward opposite poles of the
cell
Telophase
•The cell divides into two.
•The chromosomes uncoil.
•The nucleus reforms.
•The spindle apparatus disassembles.
Cytokinesis
•Not a phase of mitosis.
•Division of cytoplasm.
•Begins as the cell lengthens in anaphase and
ends with separation of daughter cells
being complete at end of telophase.
What is Meiosis?
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Meiosis produces daughter cells that have one half the number of
chromosomes as the parent cell.
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2N
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Meiosis enables organisms to reproduce sexually. Gametes (sperm and
eggs) are haploid.
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Meiosis involves two divisions producing a total of four daughter cells.
N
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Prophase I
Early
•Homologous pairs within cell become visible.
Replication of genetic material has already occurred.
Middle
•Homologous chromosomes synapse, become shorter,
thicker.
Late
•Chromosomes become double stranded.
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Crossing-over and
Recombination During
Meiosis
•Variation
•Survival of organism
Crossing over
Metaphase I
•Homologous pairs become aligned in
the center of the cell.
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Anaphase I
Centromeres on the chromosomes
do not divide. Double stranded
chromosomes move apart to
opposite poles.
Telophase I
This stage is absent in some
species.
Two haploid cell start to form (Half
the number).
Interkinesis
Interkinesis is similar to interphase
except DNA synthesis does not occur.
Chromosomes have faded from view.
Prophase II
• Nuclear envelope breaks
down and spindle apparatus
appears.
Metaphase II
• Chromosomes become
arranged on the metaphase
plate and are attached to
the now fully formed
spindle.
Anaphase II
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Centromeres separate and two chromatids of each chromosome move to
opposite poles on the spindle. Separated chromatids are now called
chromosomes.
Telophase II
• A nuclear envelope forms around each
set of chromosomes and cytokinesis
occurs, producing four daughter cells, each
with a haploid set of chromosomes
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Meiosis results
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Chromosomes fade from view.
Total of four haploid cells are
produced.
Next phase would be fertilization.
Daughter Cells
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Sexual Reproduction and
Genetic Variability
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Enhances potential for survival of
species
Genetic variability by
recombination of whole
chromosomes
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Cited Literature
 Fried, George and Hademos, George Schaum’s Outline of
Biology. New York: McGraw Hill, 2009.

Sadava, David, C. Heller, G. Orians, W. Purves, D. Hillis, Life.
The Science of Biology, Eighth Edition,Volume 1, The Cell and
Heredity. Virginia: W.H.Freeman, 2006.
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