Download Chromosomes

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
Cellular Reproduction
In asexual reproduction:
•Single-celled organisms reproduce by simple cell division
•There is no fertilization of an egg by a sperm
LM
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.
LM
Eukaryotic Chromosomes
Chromosomes
Eukaryotic
Chromosomes
DNA double helix
–The DNA in a cell is packed into
an elaborate, multilevel system of
coiling and folding.
–Nucleosomes consist of DNA
wound around histone molecules.
“Beads on
a string”
TEM
–Histones are proteins used to
package DNA in eukaryotes.
Histones
Nucleosome
Tight helical
fiber
Looped domains
TEM
Duplicated chromosomes
(sister chromatids)
Centromere
Chromosome Structure
Chromosome
unduplicated vs. duplicated
● Centromere
● Sister Chromatids
●
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)
Mitotic
phase (M)
(10% of time)
Cytokinesis
Mitosis
G2
Interphase
INTERPHASE
Centrosomes
(with centriole pairs)
Interphase
• G1: Metabolism and growth
• End of G1: Cell signaled to
divide
• S (synthesis): DNA is
duplicated
• G2: Cell forms chromosomes,
completes preparations for cell
and nuclear division
Chromatin
LM
Nuclear Plasma
envelope membrane
Prophase
and
Prometaphase
PROPHASE
Fragments of
Early mitotic
Centrosome nuclear envelope
spindle
Centromere
Chromosome, consisting
of two sister chromatids
Spindle
microtubules
Metaphase, Anaphase, Telophase
METAPHASE
Spindle
ANAPHASE
Daughter
chromosomes
TELOPHASE
Nuclear Cleavage
envelope furrow
forming
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.
Meiosis
Chromosomes
duplicate.
Homologous
chromosomes
separate.
Sister
chromatids
separate.
Pair of homologous
chromosomes in
diploid parent cell
Duplicated pair of
homologous
chromosomes
INTERPHASE BEFORE MEIOSIS
Sister
chromatids
MEIOSIS I
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.
Meiosis
How do we account for genetic variation? Cross over:
*Independent assortment
*Crossing over
*Random fertilization
Independent Assortment:
Mitosis and Meiosis