Download 201 Lec8 S13

4/26/2013
Cellular Reproduction
Cell division - A process in which a cell divides into 2 or
more cells.
Functions of cell division:
*reproduction
*growth and development
repair
*repair
Cellular Reproduction
In asexual reproduction:
•Single-celled organisms reproduce by simple cell division
•There is no fertilization of an egg by a sperm
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FUNCTIONS OF CELL DIVISION
Asexual Reproduction
Amoeba
Sea stars
African Violet
Cellular Reproduction
Sexual reproduction requires fertilization of an egg by a
sperm using a special type of cell division called meiosis.
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Eukaryotic Chromosomes
Chromosomes
Eukaryotic
Chromosomes
DNA double helix
–The DNA in a cell is packed into
an elaborate, multilevel system of
coiling and folding.
TEM
–Histones are proteins used to
k
k
t
package
DNA iin eukaryotes.
–Nucleosomes consist of DNA
wound around histone molecules.
Histones
“Beads on
a string”
Nucleosome
Tight helical
fiber
Looped domains
TEM
Duplicated chromosomes
(sister chromatids)
Centromere
Chromosome Structure
Chromosome
unduplicated vs. duplicated
● Centromere
● Sister Chromatids
●
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The Cell Cycle
S phase
(DNA synthesis;
chromosome duplication)
• The cell cycle consists
of two distinct phases
‰
‰
Interphase
Mitotic phase
G1
Interphase
(90% of time)
G2
Mitotic
phase (M)
(10% of time)
Mitosis
Cytokinesis
Interphase
INTERPHASE
Centrosomes
(with Interphase
centriole pairs)
• G1: Metabolism and growth
• End of G1: Cell signaled to
divide
• S (synthesis): DNA is
duplicated
• G2:
G2 Cell
C ll forms
f
chromosomes,
h
completes preparations for cell
and nuclear division
Chromatin
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Nuclear Plasma
envelope membrane
Prophase
and
Prometaphase
PROPHASE
Fragments of
Early mitotic
Centrosome
nuclear envelope
spindle
Centromere
Chromosome, consisting
Chromosome
of two sister chromatids
Spindle
microtubules
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Metaphase, Anaphase, Telophase
METAPHASE
Spindle
ANAPHASE
TELOPHASE
Nuclear Cleavage
envelope furrow
forming
Daughter
chromosomes
Cytokinesis
Animal cells
Plant cells
Meiosis
Sexual reproduction requires fertilization of an egg by a
sperm using a special type of cell division called meiosis.
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Meiosis
Homologous
chromosomes
separate.
Chromosomes
duplicate.
Sister
chromatids
separate.
Pair of homologous
chromosomes in
diploid parent cell
Duplicated pair of
homologous
chromosomes
Sister
chromatids
MEIOSIS I
INTERPHASE BEFORE MEIOSIS
MEIOSIS II
Meiosis
MEIOSIS I:
INTERPHASE
PROPHASE I
METAPHASE I
Centrosomes
(with centriole
pairs)
Sites of
crossing over
Microtubules
attached
to chromosome
Spindle
Nuclear
envelope
Chromatin
Sister
chromatids
Pair of
homologous
chromosomes
Chromosomes
duplicate.
Homologous
chromosomes
pair up and
exchange
segments.
ANAPHASE I
Sister chromatids
remain attached
Centromere
Pairs of
homologous
chromosomes
line up.
Pairs of
homologous
chromosomes
split up.
Meiosis
MEIOSIS II: SISTER CHROMATIDS SEPARATE
TELOPHASE I
AND
CYTOKINESIS
PROPHASE II
METAPHASE II
ANAPHASE II TELOPHASE II
AND
CYTOKINESIS
Cleavage
furrow
Sister
chromatids
separate
Two haploid
cells form;
chromosomes
are still
doubled.
Haploid
daughter
cells forming
During another round of cell division, the sister
chromatids finally separate; four haploid
daughter cells result, containing single
chromosomes.
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Meiosis
How do we account for genetic variation? Cross over:
*Independent assortment
*Crossing over
*Random fertilization
Independent Assortment:
Mitosis and Meiosis
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