Cell Reproduction
http://biofinity.org/images/Cell%20Division%20Micrograph.jpg
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Chromosome
Histone
Chromatid
Centromere
Chromatin
Sex Chromosome
Autosome
Homologous
Chromosome
Karyotype
Diploid
Haploid
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
K.
Cells with one set of chromosomes
Cells with two sets of
chromosomes
Rod-shaped structures made of
DNA and proteins
Proteins found in DNA
X and Y chromosomes
A chromosome other than a sex
chromosome
All chromosomes visible in a cell
Matching chromosomes
Copied half of a chromosome
Holds chromatids together
DNA during interphase
 Chromosome
 Histone
 Chromatid
 Centromere
 Chromatin
 Sex Chromosome
 Autosome
 Homologous Chromosome
 Karyotype
 Diploid
 Haploid
C
D
I
J
K
E
F
H
G
B
A
 Growth
and repair
 Creation of gametes (Sex Cells)
 Method of reproduction in unicellular
organisms
http://stealthisknowledge.com/Pictures/images-mesoblast_cell_division_still.jpg
 While
cells are
growing, their DNA
appears as long,
stringy chromatin
material.
 When cells are ready
to divide, the
chromatin condenses
to form
chromosomes.
http://kmarsh2.umwblogs.org/files/2008/10/mitosis_cartoon_1.jpg
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Chromosomes —DNA
wrapped around proteins
to form an X-shaped
structure
• Histones —proteins
that DNA wraps around
• Sections of
chromosomes are
called genes
• http://www.youtube.co
m/watch?v=9kQpYdC
nU14
Histones
http://activity.ntsec.gov.tw/lifeworld/english/content/images/en_gene_c5.jpg
 Each
chromosome is
made of two identical
halves called sister
chromatids held
together at a point
called a centromere.
 The sister chromatids
are the result of DNA
copying itself.
 They are called double
stranded and will
need to separate
before the cell divides.
http://www.biologycorner.com/resources/chromosome-labeled.gif
 Humans
have 46 chromosomes in the
nucleus of every cell
• Two are the sex chromosomes (X and Y)
 XX = female
 XY = male
• The other 44 are called autosomes
• They occur in matching pairs
 Called homologous chromosome pairs
 One chromosome in each pair comes from mom and
the other comes from dad
A
karyotype is
a photograph of
the matching
pairs of
chromosomes
 http://www.yout
ube.com/watch?
v=V8sNC9Cdv0
E&feature=relat
ed
http://www.mathemagic.org/MOBM/images/karyotype.jpg
 Diploid
cells contain the full set of
chromosomes (all 46)
• All body cells are diploid
 Haploid
cells contain half the number of
chromosomes (23)
• One from each homologous pair
• Sperm and egg cells are haploid
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Binary fission
Mitosis
Asexual reproduction
Meiosis
Gametes
Interphase
Cytokinesis
Prophase
Spindle fiber
Metaphase
Anaphase
Telophase
Cell plate
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
K.
L.
M.
Division of cell’s cytoplasm
Division of cell’s nucleus
Reproductive cells
Division of a prokaryotic cell
Pull chromatids apart
Chromosomes line up in middle of
the cell
Chromatids separate
Two new nuclei form
Production of offspring from one
parent
Time between cell divisions
Results in the formation of gametes
First phase of mitosis
Forms between two new plant cells
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Binary fission
Mitosis
Asexual reproduction
Meiosis
Gametes
Interphase
Cytokinesis
Prophase
Spindle fiber
Metaphase
Anaphase
Telophase
Cell plate
D
B
I
K
C
J
A
L
E
F
G
H
M
 http://www.youtube.com/watch?v=Q6uc
KWIIFmg
 How many new cells do you make every
day?
• About 2 trillion (25 million cell per second)
• Cells reproduce asexually (one parent)
 One cell becomes two
• The process is different in prokaryotes and
eukaryotes
 Prokaryotes
reproduce by
binary fission
• DNA is circular (no
chromosomes)
• DNA copies itself
• Cell divides--Simple 
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Eukaryotes use two types of cell division
• Mitosis —produces body cells
• Meiosis —produces gamete cells
• Both mitosis and meiosis happen in stages
http://ghr.nlm.nih.gov/handbook/illustrations
/mitosismeiosis.jpg
Mitosis is part of the
Cell Cycle
 Three stages in the
Cell Cycle:
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• Interphase —period of
growth, development and
DNA replication
• Mitosis —division of the
nucleus
• Cytokinesis —division of
the cytoplasm
• http://www.youtube.com/
watch?v=lf9rcqifx34&feat
ure=related
http://faculty.capebretonu.ca/cglogowski/BIOL%20101%20IMAGES/CellCycle_L.jpg
 Cells
spend most
of their time in
interphase
 Three phases
• G1—first growth
phase (Cells grow to
full size)
• S—DNA synthesis
(copied)
• G2—second growth
phase (prepares to
divide)
http://imcurious.wikispaces.com/file/view/cell_cycle.jpg/114427989/cell_cycle.jpg
 Some
cells exit the cycle after the G1
phase and enter the G0 phase. These
cells no longer divide.
• Muscle cells
• Nerve cells
 Mitosis
(division of nucleus) is divided into
four stages:
• Prophase
 DNA condenses into chromosomes
 Nuclear membrane disappears
 Centrioles and spindle fibers appear
• Metaphase
 Chromosomes line up in the middle of the cell
• Anaphase
 Sister chromatids separate and move toward poles
• Telophase
 Chromosomes uncoil back into chromatin
 Nuclear membrane forms around each set of chromosomes
Stages of Mitosis
Interphase
Prophase
Metaphase Anaphase Telophase
http://www.clt.astate.edu/mhuss/mitosis1.jpg
 The
final stage of the
cell cycle is
cytokinesis (dividing
the cytoplasm)
• In animal cells, cytokinesis
begins with a pinching in
of the membrane forming
a cleavage furrow.
• In plant cells, cytokinesis
begins with the formation
of a cell plate.
• End result is two identical
diploid daughter cells
http://www.uic.edu/classes/bios/bios100/lectf03am/cleavage.jpg
http://www.vcbio.science.ru.nl/images/cellcycle/mito_solanum_cellplate.jpg
 Meiosis
produces gamete cells (sperm
and egg cells)
• Gamete cells are haploid (half the number of
chromosomes)
• Full number of chromosomes is restored during
fertilization.
• A cell passes through interphase and copies its
DNA.
• The cell then divides twice resulting in
4 haploid gamete cells.
 Meiosis
is also
divided into stages:
• Prophase I
 Chromosomes form and
find their homologous
match
 This is called synapsis
(pairing of homologous
chromosomes)
 Each pair of homologous
chromosomes is called a
tetrad.
 Crossing over can occur
in each tetrad resulting in
a genetic recombination
of genes.
http://www.biologycorner.com/resources/crossingover.jpg
• Metaphase I
 Matching pairs of chromosomes (tetrads) line up in
the middle of the cell and attach to spindle fibers.
• Anaphase I
 Homologous chromosomes separate and move to the
poles (independent assortment)
• Telophase I and Cytokinesis I
 Nucleus and Cell both divide for the first time. This
reduces the number of chromosomes to one half. This
is called a reduction division.
 However, the chromosomes are still double stranded.
X
diploid
• Prophase II
 Spindle fibers reappear
• Metaphase II
 Chromosomes line up in the middle of the cell and
attach to spindle fibers
• Anaphase II
 Chromatids split and move to poles
• Telophase II and Cytokinesis II
 Nucleus and cell divide for the second time
 This is essentially a mitotic division.
 4 haploid gamete cells are produced. They have half
the number of single stranded chromosomes.
http://www.phschool.com/science/biology_place/labbench/lab3/images/stages2.gif
Meiosis occurs in the testes and the ovaries
Spermatogenesis —production of 4 mature sperm cells.
Oogenesis —production of 1 mature egg cell and 3
smaller polar bodies that degenerate.
http://www.biologycorner.com/resources/oogenesis.jpg
 Fertilization
—union
of sperm and egg cell.
 Sexual reproduction,
involving the
production of sperm
and egg cells by
meiosis followed by
fertilization, ensures
genetic variation in
all offspring.
http://biology.ucsd.edu/classes/bimm110.SP07/images/fertilization2.jpg