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UNIT 8: REPRODUCTION
PART 1: CELL DIVISION:
MITOSIS AND ASEXUAL
REPRO.
Introduction
Key Questions
1. Why do body-type cells need to reproduce, and
how is this accomplished?
2. Why do organisms that reproduce asexually
normally produce identical offspring?
3. Why do sex cells contain ½ the normal number of
chromosomes, and how are these cells created?
Reproduction
 MITOSIS:
 Used
for growth and tissue repair and for
asexual reproduction.
FACT!
Each minute your body needs to make about
300 MILLION NEW CELLS!
It does so by the process of MITOSIS!!!
How does Mitosis work???
 Before
a cell divides, it first COPIES (replicates)
its genetic material
 Then, the nucleus divides by MITOSIS
 Then, the cytoplasm divides to form 2 new cells
(CYTOKINESIS)
Reproduction
 Result of Mitosis:
 Formation
of 2 new genetically identical
daughter cells from 1 parent cell.
Reproduction
I. Stages of Mitosis in Animals: PMAT
Reproduction
1.
INTERPHASE
 Phase cell is in when NOT going through mitosis.
 Performing
metabolic activities to maintain
homeostasis and growing in size
 DNA is in form of chromatin
 “2n”
refers to the “normal chromosome number”
Reproduction
 If cell is to go through mitosis, it must prepare by
REPLICATING the chromosomes.
 The
chromatin doubles, so now there are 2
identical copies of the genetic material.
 2n
x 2 = 4n (what is in the cell now)
Draw Interphase
Chromatin
(doubles)
Nuclear Membrane
(disappears)
Reproduction
2. PROPHASE
 Doubled
chromatin reorganizes into
chromosomes – becomes shorter and coiled
2
pairs of centrioles move to opposite sides (or
poles) – act as anchors
Reproduction
 Prophase Continued:
 Centrioles
produce mitotic spindle and
begin to move to opposite poles
 Nuclear
membrane and nucleolus
disappear
Draw Prophase – use 2 colors
Centrioles
Doubled
Chromosomes
Reproduction
3. METAPHASE – Middle
 Chromosomes line up down middle of cell
Draw Metaphase
Spindle
Reproduction
4. ANAPHASE - Away
 Chromosomes
 Sister
split at the centromere
chromatids move away to opposite
poles, so each side has an identical copy of
each chromatid
Draw Anaphase
Reproduction
5. TELOPHASE – To normal
 Chromatids
begin to elongate and uncoil – go
back to being in form of chromatin
 Mitotic spindle disappears
 Nuclear membrane forms around each set of
chromosomes
 Nucleolus reappears
Reproduction
 LASTLY…

CYTOKINESIS – cytoplasm divides
 Results
in 2 IDENTICAL daughter cells!
Draw Telophase/Cytokinesis
Reproduction
 Is Mitosis the same in plant cells???
 The
process is very similar, but there are 2
differences:
Reproduction
1. Plant cells do not have centrioles
a
spindle does form and the chromosomes
move in the same way as animal cells
Reproduction
2. Plant cells have rigid cell walls, so they do not
pinch-in during telophase
a
cell plate forms across the middle of the cell.
 cell
plate grows outward and joins old cell wall
which divides the cell in half
Plant Cell Mitosis
Interphase of Cell Cycle
Whitefish cells
Prophase
Metaphase
Anaphase
Telophase
Animal Cell Mitosis

http://tidepool.st.usm.edu/pix/mitosis.jpg
Animations
 http://www.ai.mit.edu/lab/olympics/98/events/MI
Tosis/mitosis-animation.gif
 http://www.cellsalive.com/mitosis.htm
Videos
 Mitosis and Meiosis = (mitosis = 1-17:28)
 Mitosis – Part 1 = 4:18
 MitosisMeizisis = 27:33
What Causes Aging?
 Telomeres
 http://learn.genetics.utah.edu/content/chromosome
s/telomeres/
 Progeria (2:28)
 http://www.progeriaresearch.org/cbs-monday-
night.html
 Aging video on server – (9:06)
What is Cancer
 Cancer is uncontrolled cell division.
Applicable NY State Learning Standards
 2.1d, 4.1b, 4.1c
How do
Organisms
Reproduce
Asexually???
BY MITOSIS!!!
Define Asexual Reproduction:
 When a single parent cell
produces identical offspring by
dividing into 2 cells!
Types of Asexual
Reproduction
Type: Binary Fission
 Examples: BACTERIA and other
one-celled organisms.
 Description:
Cell
goes through mitosis
Cytoplasm divides into 2 EQUAL
parts.
Binary Fission
Type: Budding
 Examples: - yeast, hydra, and
sponges.
 Description:
Cell goes through mitosis
Cytoplasm divides into 2 UNEQUAL
parts.
Budding
Type: Sporulation
 Examples: fungi and ferns.
 Description:
Organisms
produce large numbers
(thousands) of spores by mitosis.
Spores are highly resistant cells that
can mature into adult plants.
Sporulation
Type: Regeneration
 Examples: Starfish, earthworms,
and planaria.
 Description:
Simple organisms can re-grow lost
parts.
Parent cells near missing body
parts go through mitosis.
Regeneration
Type: Vegetative
Propagation
 Examples: See below.
 Description:
Asexual
reproduction of plants
using its roots, stems, or leaves.
Vegetative Propagation
 1. Runners
 Example – strawberry plants!
 Description:
Stem
that grows sideways and has
buds!
New plant grows where runners
touch ground.
Vegetative Propagation - Runners
Vegetative Propagation
 2. Cuttings
 Example - ivy
 Description:
Piece
of a root, stem, or leaf
removed from a plant. Grow in
water, then plant in soil.
Vegetative Propagation –
Cuttings
Vegetative Propagation
 3. Grafting
 Examples: oranges, grapes
 Description:
Cut
branch from 1 tree is attached
to the base of another.
Vegetative Propagation - Grafting
Unit 8: Part 2
Meiosis
Sexual Reproduction
 The offspring are NOT identical to either
parent.
 Accomplished
through meiosis and fertilization
 Results in increased variation in species
which increases the chance of survival.
Remember:
 Mitosis
occurs in all body cells (somatic),
EXCEPT sex cells
 Body cells contain a DIPLOID (2n) –the
normal number of chromosomes.
 We have 2 chromosomes of each type (1 from
mom, 1 from dad)
 For example, humans have 23 homologous
pairs (total of 46) of chromosomes in body
cells.
Human Karyotype
We have 2 copies of each chromosome
(1 from mom and 1 from dad)
Meiosis
Part 2: Meiosis
 Organisms that reproduce SEXUALLY need
to produce sex cells that have ½ the normal
chromosome number.
Meiosis
 So, when an egg + sperm come together
(fertilization) the original chromosome
number is restored!
+
=
1n
1n
2n
 The process used to create these specialized
sex cells is MEIOSIS!!!
Meiosis
 Define: Meiosis:
 Formation
of sex cells that contain 1
chromosome of each homologous pair
(matching pairs)
Meiosis
 Result of Meiosis:
 One
cell results in the formation of 4 cells
that have ½ the number of chromosomes.
Result of Meiosis:
Meiosis
 How does MEIOSIS work???
There
are 2 divisions in meiosis:
Round
1 (when reduction occurs):
Meiosis
 INTERPHASE
Chromatin
is the same as in mitosis:
doubles
Cell prepares for meiosis
Homologous Chromosomes
Meiosis

PROPHASE I:
 The
chromosomes become shorter and more coiled as
in mitosis.
 DIFFERENCE: The replicated chromosomes line up
exactly with its homologous chromosome.
 NOTE: HOMOLOGOUS chromosomes are not
identical – but they match very closely in terms of
the genes they carry.
Meiosis
 DIFFERENCE:
 The
homologous pairs then become
attached at their centromeres forming
TETRADS – forming of the tetrads is
called SYNAPSIS.
Meiosis
 DIFFERENCE:
 When
the tetrads are together, the chromosomes
twist about each other and exchange parts or
characteristics – called CROSSING OVER.
 ***This
results in genetic variability**
Crossing Over
Prophase I
Meiosis
METAPHASE I:
 The
tetrads (homologous chromosomes and
their copies) formed in prophase line up in the
middle.
 Centromeres
of chromosomes attach to the
spindle fibers
Metaphase I
Meiosis
ANAPHASE I:

DISJUNCTION - The homologous chromosomes of
each tetrad separate and move to opposite ends of the
cell.

Each cell will receive only 1 chromosome from each
homologous pair, but that chromosome still has its sister
chromatid.
Anaphase I
Meiosis
TELOPHASE I and CYTOKINESIS:

Same as in mitosis – cytoplasm divides and results in 2
daughter cells.

BUT – each cell has half as many chromosomes as the
original cell, because each cell has only 1 chromosome
from each homologous pair.
Telophase I and Cytokinesis
Meiosis
 So, now we have 2 cells that have half of the
number of chromosomes as in the original cell,
and each chromosome still has a sister chromatid.
Meiosis

Round 2 (2nd division – much like mitosis):
 The
2 cells go right into prophase II (no doubling
of chromosomes needed, so no interphase)
Meiosis
PROPHASE II:

Each daughter cell forms a spindle and double-stranded
chromosomes move toward middle.
METAPHASE II:

Chromosomes attach to spindle fibers at their
centromeres and line up in the middle.
Prophase II
Metaphase II
Meiosis
ANAPHASE II:

The centromeres divide and the sister chromatids
separate.

These single-stranded chromosomes move to opposite
ends of the cells.
Anaphase II
Meiosis
TELOPHASE and CYTOKINESIS II:

Both daughter cells divide.

Result is 4 MONOPLOID cells – the genetic material is
different in each cell and they do not match the parent
cell!

Now we have 4 cells with single-stranded chromosomes
(1/2 the normal number).
Telophase II and Cytokinesis
Gametogenesis - Males
Gametogenesis-Females
Meiosis Animations/Videos
 On server: ‘Mitosis and Meiosis’- at 17:28-26:13