Mitosis & Meiosis
CHAPTER8
CHROMOSOMES


Chromosome: DNA in a Eukaryotic cell
that is tightly coiled and compacted in the
cell nucleus
Histones:
Proteins in
Which DNA is
Tightly wrapped
Around that
Help maintain
The shape of
The chromosomes
Chromosome Structure:




Chromosome numbers:
Chromosomes are categorized as
either sex chromosomes or
autosomes
Sex chromosomes: chromosomes
that determine the sex of an
organism
Autosomes: all other chromosomes
in an organism

Homologous chromosomes: one copy of
each autosome from each parent. The two
copies of each autosome are called
homologous chromosomes
Diploid: cells having 2 sets
Of chromosomes (2n)

Haploid: cells which contain
only one set of chromosomes (1n)

Karyotype: photomicrograph of
the chromosomes in a cell
Cell division in prokaryotes:
Binary fission
Cell Division in Eukaryotes
• Cell Cycle
– The cell cycle is the repeating set of events in
the life of a cell.
– The cell cycle consists of cell division and
interphase.
– Cell division in eukaryotes includes nuclear
division, called mitosis, and the division of
cytoplasm, called cytokinesis.
Mitosis:




If a cell wants to make a duplicate of itself, it first
must copy its DNA (part of a chromosome).
The copies then must be separated & sorted into
two sides of the cell.
The cell then splits in two. Part of each parent is
carried to the two new cells.
Results in cells such as internal organs, skin, bones,
blood, etc.
Mitosis

Mitosis animations:

http://www.youtube.com/watch?v=VlN7K1-9QB0

http://highered.mheducation.com/sites/0072495855/student_view0/chapter
2/animation__mitosis_and_cytokinesis.html
Interphase occurs just before
Mitosis begins:
 Cells spend most
of the cell cycle
in interphase
 During g1 –
offspring cells
grow to mature
size
 During S phasecells DNA is
copied
 During g2
phase- cell
prepares for cell
division (mitosis)
http://www.bioweb.uncc.edu/1110Lab/notes/notes1/lab6.htm
G0 phase
Cells can sometimes exit the cell cycle
usually from the g1 phase and enters
state called g0
 During g0, cells do not copy their DNA and
do not prepare for cell division.
 Many cells in the human body are in the
g0 phase

Interphase
Animal cell
Plant cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
st
1
step in Mitosis:
Prophase (preparation phase)
The DNA recoils,
and the
chromosomes
condense; the
nuclear membrane
disappears, and the
mitotic spindles
begin to form.
http://www.bioweb.uncc.edu/1110Lab/notes/notes1/lab6.htm
Mitosis Prophase
Animal cell
Plant cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
2nd step in Mitosis:
metaphase
The chromosomes
line up the middle
of the cell with the
help of spindle
fibers attached to
the centromere of
each replicated
chromosome.
http://www.bioweb.uncc.edu/1110Lab/notes/notes1/lab6.htm
Mitosis Metaphase
Animal cell
Plant cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
rd
3
step in Mitosis:
Anaphase (separation phase)
The chromosomes
split in the middle
and the sister
chromatids are
pulled by the
spindle fibers to
opposite poles of
the cell.
http://www.bioweb.uncc.edu/1110Lab/notes/notes1/lab6.htm
Mitosis Anaphase
Animal cell
Plant cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
th
4
step in Mitosis:
Telophase
spindle fibers
disassemble, and the
chromosomes return to a
less condensed chromatin
state.
A nuclear envelope forms
around each set of
chromosomes and a
nucleolus forms in each of
the newly formed cells.
http://www.bioweb.uncc.edu/1110Lab/notes/notes1/lab6.htm
Mitosis Telophase
Animal cell
Plant cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
After Mitosis:
Cytokinesis
The actual splitting of
the daughter cells
into
two separate cells is
called cytokinesis and
occurs differently in
both plant and animal
Cells.
Beginning of cytokinesis in a plant:
a plate forms along the
midline of the dividing cell
Beginning of cytokinesis in an animal:
cell membrane pinches in at the middle
of the dividing cell(this is called a
cleavage furrow)
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
IPMATC
http://www.youtube.com/watch?v=L0kenzoeOM
Julie Camp’s mitosis power point - http://sciencespot.net/Pages/classbio.html#Anchor-mitosis
Meiosis:

As in mitosis, if a cell wants to make a duplicate of itself,
it first must copy its DNA (part of a chromosome).

Results in reproductive cells (sperm, eggs, etc).

Part of each parent is carried to the four new cells.
Meiosis Interphase
The cell grows and
copies its DNA, and
the chromatin begins
to condense into
chromosomes.
http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html
Meiosis Prophase I
-DNA coils tightly into
chromosomes and spindle
fibers appear
-In meiosis the
homologous chromosomes
pair with one another to
form tetrads
- Portions of chromatids
may break off and attach to
adjacent chromatids, this
process is called crossing
over (When portions of
homologous chromosomes
exchange genetic material)
.Crossing over leads to
genetic recombination.
http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html
Meiosis Metaphase I
- The tetrads line up
randomly along the
midline of the cell
-Spindle fibers attach to
the centromeres of
each homologous
chromosome
http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html
Meiosis Anaphase I
-The chromosomes
move to opposite
ends of the cell.
- The random
separation of the
homologous
chromosomes is
called independent
assortment
http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html
Meiosis Telophase I & Cytokinesis
The cell begins to
divide into two
daughter cells. It is
important to
understand that each
daughter cell can get
any combination of
maternal and paternal
chromosomes.
http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html
Meiosis Prophase II
Spindle fibers form and begin moving
chromosomes toward the middle of the cell
http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html
Meiosis Metaphase II
As in Meiosis I, the
chromosomes line up
on the spindle fibers
at the midline of the
cell.
http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html
Meiosis Anaphase II
The two cells each
begin to divide. As in
Meiosis I, the
chromosomes move
to opposite ends of
each cell.
http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html
Telophase II & Cytokinesis
-
-
- a nuclear membrane forms around the
chromosomes in each of the four new cells.
Cytokinesis II then occurs.
- each new cell contains half the original cells
number of chromosomes
http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html
Comparing Mitosis and Meiosis

Mitosis




2 daughter cells
Diploid (2n)
Genetically identical
Meiosis



4 daughter cells
Haploid (1n)
Not genetically identical
http://www.youtube.com/watch?v=zGVBAH
AsjJM&feature=g-vrec
http://www.youtube.com/watch?v=qCLmR9
-YY7o