Transcript Cell Cycle & Cell Division

Types of Cell Reproduction
Asexual reproduction involves a
single cell dividing to make 2 new,
identical daughter cells
Mitosis & binary fission are
examples of asexual reproduction
Sexual reproduction involves two
cells (egg & sperm) joining to make a
new cell (zygote) that is NOT
identical to the original cells
Meiosis is an example
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Review
of
Mitosis
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Mitotic Stages:
Interphase
Cleavage
Furrow
Prophase
Telophase
Metaphase
plate
Metaphase
Anaphase
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Eukaryotic Cell Division
 Used for growth and
repair
 Produce two new cells
identical to the original
cell
 Cells are diploid (2n)
Prophase
Metaphase
Chromosomes during
Metaphase of mitosis
Anaphase Telophase Cytokinesis
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Mitosis Animation
Name each stage as you see it occur?
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Locate the Four Mitotic
Stages in Plants
Anaphase
Telophase
Metaphase
Prophase
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Uncontrolled Mitosis
 If mitosis is not
controlled, unlimited
cell division occurs
causing cancerous
tumors
 Oncogenes are special
proteins that
increase the chance
that a normal cell
develops into a tumor
cell
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Cancer cells
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Meiosis
Formation of Gametes
(Eggs & Sperm)
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Facts About Meiosis
Preceded by interphase which
includes chromosome replication
Two meiotic divisions --- Meiosis
I and Meiosis II
Called Reduction- division
Original cell is diploid (2n)
Four daughter cells produced that
are monoploid (1n)
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Facts About Meiosis
Daughter cells contain half the
number of chromosomes as the
original cell
Produces gametes (eggs & sperm)
Occurs in the testes in males
(Spermatogenesis)
Occurs in the ovaries in females
(Oogenesis)
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Remember:
• FSH-follicle stimulating hormone regulated
by Pituitary gland regulates meiosis in egg
and sperm.
• Case study: Eric- dr’s removed his damaged
Pituitary gland. So a side effect would be
low sperm count. He still produced
testosterone bc that is regulated by testes.
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More Meiosis Facts
 Start
with 46 double stranded
chromosomes (2n)
After 1 division - 23 double
stranded chromosomes (n)
After 2nd division - 23 single
stranded chromosomes (n)
 Occurs in our germ cells that
produce gametes-NOT SOMATIC
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Why Do we Need Meiosis?
It is the fundamental basis of
sexual reproduction-more
genetic variation
Two haploid (1n) gametes are
brought together through
fertilization to form a diploid
(2n) zygote
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Fertilization – “Putting it
all together”
2n = 6
1n =3
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Replication of Chromosomes
Replication is the
process of
duplicating a
Occurs in
chromosome
Interphase
Occurs prior to
division-”S phase”
Replicated copies
are called sister
chromatids
Held together at
centromere
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A Replicated Chromosome
Gene X
Sister
Chromatids
Homologs
(same genes,
different alleles)
(same genes,
same alleles)
Homologs separate in meiosis I and
therefore different alleles separate.
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Meiosis Forms Haploid Gametes
 Meiosis must reduce the chromosome number
by half
 Fertilization then restores the 2n number
from mom
from dad
child
too
much!
meiosis reduces
genetic content
The right
number!
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Meiosis: Two Part Cell
Division
Sister
chromatids
separate
Homologs
separate
Meiosis
I
Meiosis
II
Diploid
Diploid
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Haploid
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Meiosis I: Reduction Division
Spindle
fibers
Nucleus
Early
Prophase I
(Chromosome
number
doubled)
Late
Prophase
I
Nuclear
envelope
Metaphase
Anaphase Telophase I
I
I
(diploid)
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Prophase I
Early prophase
Homologs pair.
Crossing over
occurs.
Late prophase
Chromosomes condense.
Spindle forms.
Nuclear envelope
fragments.
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Can crossover occur between 2
different chromosomes?
• Yes, but scientists refer to this as a
mutation.
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Tetrads Form in Prophase I
Homologous chromosomes
(each with sister
chromatids)
Join to form a
TETRAD
Process Called Synapsis
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Crossing-Over
 Homologous
chromosomes in
a tetrad cross
over each other
 Pieces of
chromosomes or
genes are
exchanged
 Produces
Genetic
recombination in
the offspring
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Homologous Chromosomes
During Crossing-Over
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Crossing-Over
Crossing-over multiplies the already huge
number of different gamete types
produced bycopyright
independent
assortment 25
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Metaphase I
Homologous pairs
of chromosomes
align along the
equator of the
cell
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Anaphase I
Homologs separate and
move to opposite poles.
Sister chromatids remain
attached at their
centromeres.
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Telophase I
Nuclear envelopes
reassemble.
Spindle disappears.
Cytokinesis divides cell
into two.
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Meiosis II
Gene X
Only one homolog of each
chromosome is present in
the cell.
Sister chromatids carry
identical genetic
information.
Meiosis II produces gametes with
one copy of each chromosome and
thus one copy of each gene.
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Meiosis II: Reducing
Chromosome Number
Prophase
II
Metaphase
Telophase
II
Anaphase
4 Genetically
II
II
Different
haploid cells
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Prophase II
Nuclear envelope
fragments.
Spindle forms.
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Metaphase II
Chromosomes align
along equator of cell.
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Anaphase II
Equator
Pole
Sister chromatids
separate and
move to opposite
poles.
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Telophase II
Nuclear envelope
assembles.
Chromosomes
decondense.
Spindle disappears.
Cytokinesis divides
cell into two.
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Results of Meiosis
Gametes (egg & sperm)
form
Four haploid cells with
one copy of each
chromosome
One allele of each gene
Different combinations
of alleles for different
genes along the
chromosome
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Meiosis Animation
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Comparing
Mitosis and
Meiosis
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Comparison of Divisions
Mitosis
Meiosis
2
Number of
divisions
1
Number of
daughter cells
2
4
Yes
No
Same as parent
Half of parent
Where
Somatic cells
Germ cells
When
Throughout life
At sexual maturity
Genetically
identical?
Chromosome #
Role
Growth and
repair
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Sexual reproduction
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