Chromosomes, Mitosis and
Meiosis
Chapter 10
Learning Objective 1
•
What is the significance of chromosomes
in terms of information?
Chromosomes
Organization
•
Genes
•
•
•
Chromatin
•
•
•
cell’s informational units
made of DNA
DNA and protein
makes up chromosomes (eukaryotes)
Chromosomes
•
•
allow DNA sorting
into daughter cells
KEY CONCEPTS
•
In eukaryotic cells, DNA is wound around
specific proteins to form chromatin, which
in turn is folded and packaged to make
individual chromosomes
Learning Objective 2
•
How is DNA organized in prokaryotic and
eukaryotic cells?
Prokaryotic Cells
•
Contain circular DNA molecules
Eukaryotic Chromosomes
•
Nucleosome
•
•
•
histone (protein) bead wrapped in DNA
organized into coiled loops
held together by nonhistone scaffolding
proteins
Nucleosomes
DNA wound around a
cluster of histone
molecules
Histone tails
Linker DNA
Nucleosome
(10 nm diameter)
Fig. 10-2a, p. 213
100 nm
Fig. 10-2b, p. 213
Scaffolding Proteins
DNA
Scaffolding
proteins
2 μm
Fig. 10-3, p. 213
Chromosome Organization
1400 nm
700 nm
300 nm fiber (looped domains)
30 nm chromatin fiber
DNA
wound
around a
cluster of
histone
molecules
Condensed Condensed Scaffolding
chromosome chromatin protein
Extended
chromatin
Packed nucleosomes
Histone
10 nm
2 nm
DNA double helix
Nucleosomes
Fig. 10-4, p. 214
Learning Objective 3
•
What are the stages in the eukaryotic cell
cycle, and their principal events?
Eukaryotic Cell Cycle
•
Cycle of cell division
•
•
interphase
M phase
INTERPHASE
G1
(First gap phase)
S
(Synthesis phase)
G2
(Second gap
phase)
M PHASE
(Mitosis and cytokinesis)
Fig. 10-5, p. 215
Interphase
•
First gap phase (G1 phase)
•
•
Synthesis phase (S phase)
•
•
•
cell grows and prepares for S phase
DNA and chromosome protein synthesis
chromosome duplication
Second gap phase (G2 phase)
•
•
protein synthesis increases
preparation for cell division
M Phase
•
Mitosis
•
•
•
nuclear division
two nuclei identical to parent nucleus
Cytokinesis
•
•
cytoplasm divides
two daughter cells
KEY CONCEPTS
•
Cell division is an important part of the cell
cycle, which consists of the successive
stages through which a cell passes
Animation: The Cell Cycle
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Learning Objective 4
•
What is the structure of a duplicated
chromosome, including the sister
chromatids, centromeres, and
kinetochores?
A Duplicated Chromosome
•
Consists of a pair of sister chromatids
•
•
Centromere
•
•
•
containing identical DNA sequences
constricted region
joins sister chromatids
Kinetochore
•
•
protein to which microtubules bind
attached to centromere
Sister Chromatids
Centromere
region
Microtubules
Kinetochore
Sister chromatids
1.0 μm
Fig. 10-7, p. 218
Learning Objective 5
•
What is the process and significance of
mitosis?
Mitosis
•
Preserves chromosome number
•
•
in eukaryotic cell division
Identical chromosomes are distributed to
each pole of the cell
•
nuclear envelope forms around each set
Interphase
INTERPHASE
Chromatin
PROPHASE
Nucleolus
Nucleus
Pieces of
nuclear
envelope
PROMETAPHASE
Sister chromatids
of duplicated
chromosome
Spindle
microtubule
Nuclear envelope
Centrioles
Plasma
membrane
Kinetochore
Developing mitotic
spindle
Fig. 10-6a, p. 216
Prophase
•
•
•
Chromatin condenses into duplicated
chromosomes (pair of sister chromatids)
Nuclear envelope begins to disappear
Mitotic spindle begins to form
Mitotic Spindle
Metaphase plate
(cell’s midplane)
Kinetochore
microtubule (spindle
microtubule)
Centrioles
Astral microtubules
Pericentriolar
material
Polar (nonkinetochore)
microtubule
Sister chromatids
Fig. 10-9a, p. 219
10 μm
Fig. 10-9b, p. 219
Prophase
Prometaphase
•
•
Spindle microtubules attach to
kinetochores of chromosomes
Chromosomes begin to move toward cell’s
midplane
Prometaphase
Metaphase
•
•
•
Chromosomes align on cell’s midplane
(metaphase plate)
Mitotic spindle is complete
Microtubules attach kinetochores of sister
chromatids to opposite poles of cell
Metaphase
Anaphase
•
Sister chromatids separate
•
•
move to opposite poles
Each former chromatid is now a
chromosome
Anaphase
Telophase
•
•
•
•
•
Nuclear envelope re-forms
Nucleoli appear
Chromosomes uncoil
Spindle disappears
Cytokinesis begins
Telophase
ANAPHASE
TELOPHASE
25 μm
METAPHASE
Spindle
Cleavage furrow
Centriole
pair at
spindle
pole
Cell’s midplane
(metaphase plate)
Daughter
chromosomes
Reforming
nuclear envelope
Fig. 10-6b, p. 217
KEY CONCEPTS
•
In cell division by mitosis, duplicated
chromosomes separate (split apart) and
are evenly distributed into two daughter
nuclei
Cytokinesis
Cleavage
furrow
Actomyosin
contractile ring
10 μm
Fig. 10-10a, p. 220
Vesicles
gather on
cell’s
midplane
Plasma
Cell
membrane wall
Small
vesicles
fuse,
forming
larger
vesicles
Cell plate
forming
Eventually
one large
vesicle
exists
New cell
walls (from
vesicle
contents)
New plasma
membranes
(from vesicle
membranes)
Cell plate
Nucleus forming
5 μm
Fig. 10-10b, p. 220
Learning Objective 6
•
How is the cell cycle controlled?
Cell-Cycle Control
•
Cyclin-dependent kinases (Cdks)
•
•
•
protein kinases that control cell cycle
active only when bound to cyclins
Cyclins
•
•
regulatory proteins
levels fluctuate during cell cycle
Cyclins
1
5
Cdk
G1
1
2
1 Cyclin is synthesized and accumulates.
3
3 M-Cdk phosphorylates proteins,
activating those that facilitate mitosis
and inactivating those that inhibit
mitosis.
4 An activated enzyme complex
recognizes a specific amino acid
sequence in cyclin and targets it for
destruction. When cyclin is degraded,
M-Cdk activity is terminated, and the
cells formed by mitosis enter G1.
5 Cdk is not degraded but is recycled
and reused.
S
4
M
G2
Cyclin
4
Degraded
cyclin
5
2 Cdk associates with cyclin, forming a
cyclin–Cdk complex, M-Cdk.
2
3
M-Cdk
(triggers
M phase)
Cdk
Fig. 10-12, p. 222
KEY CONCEPTS
•
An internal genetic program interacts with
external signals to regulate the cell cycle
Learning Objective 7
•
What is the difference between asexual
and sexual reproduction?
Asexual Reproduction
•
Single parent
•
•
offspring have identical hereditary traits
Mitosis
•
basis for eukaryotic asexual reproduction
Binary
Fission
Plasma
membrane
Cell wall
Origin of
replication
Prokaryotic cell
Bacterial
DNA
Two copies
of bacterial
DNA
1 DNA replication begins at
single site on bacterial
DNA.
2 Replication continues, as
replication enzymes work
in both directions from
site where replication
began.
3 Replication is completed.
Cell begins to divide, as
plasma membrane grows
inward.
4 Binary fission is
complete. Two identical
prokaryotic cells result.
Two identical prokaryotic cells
Fig. 10-11, p. 221
Sexual Reproduction
•
•
Two haploid sex cells (gametes) fuse to
form a single diploid zygote
Meiosis
•
produces gametes
Learning Objective 8
•
•
What is the difference between haploid
and diploid cells?
What are homologous chromosomes?
Diploid Cell
•
Chromosomes are paired (homologous
chromosomes)
•
•
similar in length, shape, other features
carry genes affecting the same traits
Haploid Cell
•
Contains only one member of each
homologous chromosome pair
Fig. 10-16, p. 229
MITOSIS
PROPHASE
No synapsis of
homologous
chromosomes
ANAPHASE
Sister chromatids
move to opposite
poles
DAUGHTER
CELLS
Two 2n cells with
unduplicated
chromosomes
Fig. 10-16a, p. 229
MEIOSIS
PROPHASE I
Synapsis of homologous
chromosomes to form
tetrads
ANAPHASE I
Homologous
chromosomes move
to opposite poles
PROPHASE II
Two n cells with
duplicated
chromosomes
ANAPHASE II
Sister chromatids
move to opposite
poles
HAPLOID CELLS
Four n cells with
unduplicated
chromosomes
Fig. 10-16b, p. 229
Learning Objective 9
•
What is the process and significance of
meiosis?
Meiosis
•
•
One diploid cell divides two times, yielding
four haploid cells
Sexual life cycles in eukaryotes require
meiosis
•
each gamete contains half the number of
chromosomes in parent cell
Meiosis I
•
Prophase I
•
•
Crossing-over
•
•
•
homologous chromosomes join (synapsis)
between homologous (nonsister) chromatids
exchanges segments of DNA strands
Results in genetic recombination
Synapsis
Maternal sister
chromatids
Paternal
sister
chromatids
Synaptonemal
complex
Chromatin
Protein
Chromatin
Maternal sister
chromatids
Fig. 10-14a, p. 228
Chromosome
Synaptonemal
complex
Chromosome
0.5 μm
Fig. 10-14b, p. 228
Meiosis I
•
Metaphase I
•
•
Anaphase I
•
•
•
tetrads (homologous chromosomes joined by
chiasmata) line up on metaphase plate
homologous chromosomes separate
distributed to different nuclei
Each nucleus contains haploid number of
chromosomes
•
each chromosome has 2 chromatids
Tetrads and Chiasmata
Sister
chromatids
Chiasmata
Kinetochores
Sister
chromatids
1 μm
Fig. 10-15a, p. 228
Sister
chromatids
Chiasmata
Kinetochores
Fig. 10-15b, p. 228
Meiosis II
•
Two chromatids of each chromosome
separate
•
•
one distributed to each daughter cell
Each former chromatid is now a
chromosome
Meiosis
Meiosis
INTERPHASE
MEIOSIS I
Mid-prophase I
Nucleolus
Nuclear envelope
Chromatin
Centrioles
Interphase
preceding meiosis;
DNA replicates.
Late prophase I
Homologous
chromosomes
Developing
meiotic spindle
Homologous chromosomes
synapse, forming tetrads;
nuclear envelope breaks down.
Fig. 10-13a (1), p. 226
MEIOSIS II
Prophase II
Metaphase II
Anaphase II
Daughter
chromosomes
Chromosomes condense
again following brief
period of interkinesis.
DNA does not replicate
again.
Chromosomes line up
along cell's midplane.
Sister chromatids separate,
and chromosomes move to
opposite poles.
Fig. 10-13a (2), p. 226
Anaphase I
Metaphase I
Telophase I
Microtubule
attached to
kinetochore
Sister
chromatids
Tetrads line up on cell's
midplane. Tetrads held
together at chiasmata
(sites of prior crossingover).
Cleavage furrow
Separation of
homologous
chromosomes
Homologous chromosomes
separate and move to
opposite poles. Note that
sister chromatids remain
attached at their
centromeres.
One of each pair of
homologous
chromosomes is at
each pole.
Cytokinesis occurs.
Fig. 10-13b (1), p. 227
Telophase II
Four haploid cells
25 μm
Nuclei form at opposite poles of
each cell. Cytokinesis occurs.
Four gametes (animal) or four
spores (plant) are produced.
Fig. 10-13b (2), p. 227
Learning Objective 10
•
What are the different processes and
outcomes of mitosis and meiosis?
Mitosis
•
•
•
Single nuclear division
2 daughter cells genetically identical to
each other and to original cell
No synapsis of homologous chromosomes
Mitosis
Meiosis
•
•
Two successive nuclear divisions form
four haploid cells
Synapsis of homologous chromosomes
occurs during prophase I
Meiosis
KEY CONCEPTS
•
Meiosis, which reduces the number of
chromosome sets from diploid to haploid,
is necessary to maintain the normal
chromosome number when two cells join
during sexual reproduction
KEY CONCEPTS
•
Meiosis helps to increase genetic variation
among offspring
Learning Objective 11
•
Compare the roles of mitosis and meiosis
in various generalized life cycles
Animals
•
Somatic cells are diploid
•
•
produced by mitosis
Gametes are haploid
•
produced by meiosis (gametogenesis)
Animal Life Cycle
Gametes (n)
Meiosis
Fertilization
Zygote (2n)
Mitosis
Multicellular
diploid
organism
(2n)
Animals
Fig. 10-17a, p. 230
Simple Eukaryotes
•
May be haploid
•
•
produced by mitosis
Only diploid stage is the zygote
•
which undergoes meiosis to restore the
haploid state
Simple Eukaryote Life Cycle
Unicellular or
multicellular
haploid organism
(n)
Mitosis
Mitosis
Gametes (n)
Meiosis
Fertilization
Zygote (2n)
Simple eukaryotes
Fig. 10-17b, p. 230
Plants
•
Alternation of generations:
•
•
sporophyte generation
gametophyte generation
Plants
•
Sporophyte generation
•
•
•
multicellular diploid
forms haploid spores by meiosis
Spore divides (mitosis) to form
gametophyte generation
•
•
multicellular haploid
produces gametes by mitosis
Plants
•
•
Two haploid gametes fuse to form diploid
zygote
Zygote divides (mitosis) to produce new
diploid sporophyte generation
Plant Life Cycle
Gametophyte (n)
(multicellular haploid
organism)
Mitosis
Mitosis
Spores (n)
Gametes (n)
Fertilization
Meiosis
Zygote (2n)
Mitosis
Sporophyte (2n)
(multicellular diploid
organism)
Plants, some algae, and some fungi
Fig. 10-17c, p. 230
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