Download Cell Cycle, Mitosis, and Meiosis

Cell Cycle, Mitosis, and
Meiosis
Cell Division and Death
• Are required for normal growth and
development.
• Mitosis produces new cells
– Mitosis occurs in somatic cells (all cells but
egg and sperm)
• Apoptosis is cell death that is part of
normal development
• Necrosis is cell death in response to
injury
The Cell Cycle
The sequence of events associated with cell
division
Figure 2.15
• S phase: DNA
synthesis
• G phase: gap for
growth
• M phase: mitosis
(nuclear division)
• Cell division or
cytokinesis is part of
G1
Stages of the Cell Cycle
• Interphase
– Prepares for cell division
– Replicates DNA and subcellular
structures
– Composed of G1, S, and G2
• Mitosis division of the nucleus
• Cytokinesis division of the cytoplasm
Replication of Chromosomes
• Process of duplicating
chromosomes during
S phase
• Occurs prior to
division
• Produces sister
chromatids held
together at
centromere
Mitosis
•Produces two identical daughter cells
•Chromosomes align
•Sister chromatids separate and move to
opposite poles.
•Nuclear membranes form around each
new nucleus
•Division of cytoplasm or cytokinesis
occurs.
Overview of Mitosis
• Continuous process divided
into
– Prophase
– Metaphase
– Anaphase
– Telophase
Mitosis in a Human Cell
Figure 2.17
Prophase
• Replicated
chromosomes
condense
• Microtubules
organize into a
spindle
• Nuclear membrane
breaks down
Figure 2.17
Metaphase
• Chromosomes line
up on the
metaphase plate
• Spindle
microtubules are
attached to
centromeres of
chromosomes
Figure 2.17
Anaphase
• Centromeres
separate
• Chromosomes
move to opposite
ends of the cell
Figure 2.17
Telophase
• Chromosomes
uncoil
• Nuclear membranes
form
• Spindle disappears
Figure 2.17
Cytokinesis
• Cytoplasmic division
• occurs after nuclear division is
complete.
• Two cells are formed.
Gametes
• Form from cell division of germ line cells
• Meiosis is cell division to produce gametes
• Meiosis has two divisions of the nucleus
(Meiosis I and Meiosis II) and produces
cells with half the number of
chromosomes (haploid)
Homologous Chromosomes
• Carry the same genes
• Pair during Meiosis I
• Separate in the
formation of gametes
• One copy of each pair
is from the mother and
one is from the father.
Figure 1.3
Meiosis I : homologous
chromosomes separate
Spindle
fibers
Nucleus
Nuclear
envelope
Prophase I
(early)
(diploid)
Figure 3.4
Prophase I
(late)
(diploid)
Metaphase I
(diploid)
Anaphase I
(diploid)
Telophase I
(diploid)
Meiosis II : sister chromatids
separate
Prophase II
(haploid)
Figure 3.4
Metaphase II
(haploid)
Anaphase II
(haploid)
Telophase II
(haploid)
Four
nonidentical
haploid
daughter cells
Results of Meiosis
Gametes
•Four haploid cells
•Contain one copy of
each chromosome and
one allele of each gene
•Each cell is unique
Figure 3.4
Recombination (crossing over)
• Occurs in prophase of
meiosis I
A
A
B
B
C
• Homologous
chromosomes exchange
genes
F
• Generates diversity
b
C
D D
E
E
F
Figure 3.5
a
a
e
f
c
b
c
d
d
e
f
Recombination (crossing over)
A
a
B
• Exchange between
homologs
• Occurs in prophase I
C
C
c
D D
E
F
d
E
F
e
f
Figure 3.5
Letters denote genes and case denotes alleles
b
c
d
e
f
Recombination (crossing over)
a
A
B
b
C
•Creates chromosomes
with new combinations of
alleles for genes A to F
D
E
F
A
a
B
c
b
c
d
d
C
D
E
F
Figure 3.5
e
f
e
f