3 Explanation - Mitosis and Meiosis Presentation - Standard Version.pptx

Vers. 07/2020 © Kesler Science, LLC
Mitosis and
Meiosis
Presented by Kesler Science

© Kesler Science, LLC
Mitosis and Meiosis
Essential Questions:
Reflect on the Essential
Questions before you dive in…
1. If you were quizzed today,
which questions would you know
the answers to already?
2. Which questions would you
need to learn more about to
answer confidently?
1. What are mitosis
and meiosis?
2. What occurs at
different phases in
cell division?
3. How are mitosis
and meiosis similar
and different?

Mitosis and Meiosis
Vocabulary
Cell: Smallest structural and functional unit of an
organism. Our bodies are made of them.
Somatic cell: All cells in the body, except for germ cells
Germ cell: Contain half of the number of
chromosomes. Only found in the ovaries and testes
(reproductive organs)
Cell division: How cells reproduce by splitting apart.
There are two types: Mitosis and Meiosis.
Mitosis: The way in which somatic cells divide
Meiosis: The ways in which germ cells divide
Type of Cell: somatic germ
Divides by: mitosis meiosis I&II
# of
Chromosomes:
46
(in humans)
23
Location in
body:
Found all
over the
body
Reproductive
system
(testes and
ovaries)
Differences in Cell Division

Mitosis and Meiosis
Vocabulary
chromatin – unwound
DNA found in the nucleus
chromosome – tightly
packed DNA, found only
during cell division. Can be
seen with a microscope
What is the difference between
chromatin and chromosomes?
chromatin chromosome

Mitosis and Meiosis Vocabulary
chromatid – each of two
thread-like strands into
which a chromosome divides
during mitosis
sister chromatids –
two identical copies of a
chromatid
centromere – a structure in
a chromosome that holds the
two chromatids together
What does a
centromere hold
together?
Image by bioninja: Cornell, B. 2016. http://ib.bioninja.com.au

Mitosis and Meiosis
Vocabulary
spindle fibers – controls the
movement and separation of
chromosomes during division
centriole – helps in the
formation of spindle fibers
nuclear envelope – a
membrane that separates the
nucleus from the cytoplasm in
eukaryotic cells
centrioles
nuclear envelope is
breaking down spindle fibers
nuclear envelope is
broken down

Mitosis
Somatic cells
• Use mitosis for cell division.
• Contains 46 chromosomes
in humans
• Found throughout the body:
Blood vessels
Blood cells
Bone Marrow
Brain
Muscles
Skin
Teeth
Intestines and other internal organs
Image credits: commons.wikimedia.org:
Cardiac muscle by OpenStax College -
Anatomy & Physiology, Connexions
http://cnx.org/content/col11496/1.6/, Jun
19, 2013., CC BY 3.0 Spinal Cord motor
neuron and red blood cells by Fayette A
Reynolds M.S, Berkshire Community College
Bioscience Image Library

Mitosis
Credits: David O Morgan-The Cell Cycle. Principles of Control. commons.wikimedia.org. TheAlphaWolf - CC BY-SA 3.0, commons.wikimedia.org
Stages of early mitosis in a vertebrate cell with
micrographs of chromatids
Cell Division by Mitosis
Mitosis in somatic cells results in two cells
exactly the same as the parent cell
The two new cells are diploid cells
Mitosis involves one “set” of division stages
Mitosis results in
diploid (2) cells

Mitosis
Mitosis creates new cells
that can be used for cell
growth and repair.
This image shows a recent cell division and the resulting two
daughter cells, including two nuclei and unwinding chromosomes.
After a cell goes
through mitosis, how
many cells are there?

Mitosis
Mitosis is also used for
asexual reproduction:
1. budding
2. vegetative
reproduction
3. binary fission
4. fragmentation
(Examples: some types
of jellyfish, worms, and
plants)

Mitosis
• Four basic phases
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase/Cytokinesis
By
Ali
Zifan
CC
BY-SA
4.0
commons.wikimedia.org
• Occurs in a strict sequential order called
the cell cycle
• Produces diploid cells (2) with the same
genetic makeup as parent cell

Mitosis
Prophase
First phase of mitosis
• Chromosomes condense and
become visible through a
microscope
• Spindles begin to form
• The nuclear membrane
breaks down
• Centrioles begin moving
toward the poles
The nuclear membrane breaks
apart to allow the contents to be
used in mitosis. What is stored
in the nucleus? chromosomes
spindles
nuclear
membrane
centrioles

Mitosis
Metaphase
Second phase of mitosis
• The chromosomes, guided by the spindle
(microtubule) fibers, line up in the middle of the
dividing cell
• The centrosomes are at opposite ends (spindle poles)
of the cell
centrosome
spindle fibers
chromosomes
By
Ali
Zifan
CC
BY-SA
4.0
centrosome - an organelle near the nucleus of a
cell that contains the centrioles (in animal cells)
and from which the spindle fibers develop in cell
division

Mitosis
Anaphase
Third phase of mitosis
• The two sister chromatids of each chromosome are
pulled apart by the spindle fibers
• Chromatids move away from each other toward the
poles; now each one is called a chromosome
• The cell elongates so that the poles are farther
apart
Why does the cell get longer during anaphase??
chromosomes
spindle fibers

Mitosis
Telophase (and cytokinesis)
The last phase of mitosis
• The chromosomes have reached
the poles and begin to unwind
• Two new nuclear envelopes form
around each of the two
separated sets of chromosomes
(forming two nuclei in one cell)
cleavage furrow
at midbody
new nuclear
envelopes
forming
By Ali Zifan CC BY-SA 4.0 commons.wikimedia.org
Fluorescent scan of
final stage of mitosis
• The cleavage furrow begins separating the cytoplasm
into two cells, each with a nucleus (this is cytokinesis)
• When complete, the cell has divided into two daughter
cells exactly like the parent cell

Mitosis Interphase
Occurs between mitosis
cycles
• Chromatin is unwound
• The cell grows in
preparation for cell
division
• Note the position of the
centrioles
• Just before mitosis starts,
single chromosomes
replicate to make a pair
of long, stringy sister
chromatids
centrioles
unwound
chromatin
nucleolus
By
Ali
Zifan
CC
BY-SA
4.0
nucleus
Where is the
chromatin during
interphase?

Think About It
Mitosis was named in 1882 by a German scientist.
The name was taken from the ancient Greek word
mitos, which means “string”. What parts of mitosis
may have inspired this name?

Meiosis
Germ cells
• Found only in reproductive
organs
• spermatozoa (sperm
cells)
• ova (egg cells)
• 23 chromosomes
• Divide by meiosis
Which cells are more common in the
human body, germ cells or somatic cells?
Credits: Ciencias Españolas CC BY-SA 3.0, wikimedia.org. www.medicalgraphics.de CC-BY-ND 4.0
Here are microscopic images of
human sperm (spermatozoa) and
egg (ova) cells

Meiosis
Cell Division by Meiosis I and II
• Meiosis in germ cells results in a variety of genetically different offspring
• Involves two “sets” of division stages (meiosis I & II)
Meiosis results in haploid (4) cells
By Rdbickel - Own work, CC BY-SA 4.0, commons.wikimedia.org
Four haploid
daughter cells

Meiosis
Meiosis
• Reduces the number of
chromosomes in the parent
cell by half
• Produces four gamete cells
• Meiosis is required to
produce ova and sperm cells
for sexual reproduction
What is meiosis?
sperm
ova
(or egg)

Meiosis
Crossing Over
Meiosis Vocabulary
• homologous chromosomes – During meiosis, the
matching paternal (from the father) and maternal
(from the mother) chromosomes pair up inside a
cell
• crossover – This is the process where homologous
chromosomes pair up and exchange genetic
material to form new chromosomes
• haploid cells – Four cells form as a result of
meiosis. Each one is genetically different from
each other and the parent cells

Meiosis
By Ali Zifan - Own work; Campbell Biology (10th Edition) by: Jane B. Reece & Steven A. Wasserman., commons.wikimedia.org/
Meiosis cell division occurs in two sets of stages, meiosis I and II
Meiosis I Meiosis II

Meiosis
Meiosis I – Prophase I
First phase of meiosis I
• Chromosomes become
visible under a microscope
as they condense
• Homologous chromosome
pairs align and crossover
occurs
• Nuclear envelope disappears
• Spindles enter nucleus
What is the role of the spindle fibers?
(Hint, it is the same as mitosis.)
centrioles
spindles
homologous chromosomes
nuclear envelope
fragments
Image by Ali Zifan - Own work; CC BY-SA 4.0, commons.wikimedia.org/

Meiosis
Meiosis I – Prophase I
What is “crossover”?
• Crossover is part of
prophase I
• Crossover “swaps” genetic
material between two
homologous chromosomes
The result is more genetic
diversity This shows the crossing-over process,
which occurs in the nucleus.
https://cnx.org/contents/GFy_h8cu@10.8:GYZS3DDP@8/The-Process-of-Meiosis CC BY-SA 4.0

Meiosis
Meiosis I – Metaphase I
Second phase of meiosis I
• Crossover is complete
• Homologous chromosome
pairs move toward the
center and line up
• Spindle fibers attach to the
centromere of each
chromosome
Image by Ali Zifan - Own work; Campbell Biology (10th Edition) by: Jane B. Reece & Steven A. Wasserman., CC BY-SA 4.0, commons.wikimedia.org/
What is crossover?

Think About It
The names of the phases of cell division were inspired by ancient Greek
words. For each of these prefixes, describe why that Greek meaning is a
good fit for the phase it names.
prefix meanings explain
pro- before; in front of
meta- after; in the middle of
ana- again; return
telo- end; completion

Meiosis
Meiosis I – Anaphase I
Third phase of meiosis I
• Cell starts to lengthen
• Two of each chromosome
pairs separate and are pulled
by the spindle fibers toward
opposite poles
• In meiosis, the chromatids
remain together. This is in
contrast to mitosis, where
sister chromatids separate
sister chromatids
remain together
spindle fibers
homologous
chromosomes
move to opposite
poles of the cell
What remains together and what separates
during anaphase I?

Meiosis
Meiosis I – Telophase I
Fourth phase of meiosis I
• Complete haploid (4) sets
of chromosomes
• A cleavage furrow appears
• By the end of the stage the
parent cell has divided into
two daughter cells
• This separation of
cytoplasm is called
cytokinesis
2 new daughter
cells form
cleavage furrow
What is cytokinesis?

Meiosis
Interkinesis in Meiosis
• A period of rest
• No replication of DNA
occurs during this phase
daughter
cells
unwound
chromatin
centrioles
nucleus
How many cells were there at
the start of meiosis?
How many cells are there now,
at interkinesis?

Meiosis
Meiosis II – Prophase II
First phase in meiosis II
• Begins with two daughter cells from meiosis I
• Chromosomes are condensed
• Nuclear envelope begins to break down
• Centrosomes have replicated and are moving toward
the poles
Notice there are two
cells now from meiosis I
centrioles
chromosomes
nuclear
envelope
spindles form
around
chromosomes

Meiosis
Meiosis II – Metaphase II
Second phase of meiosis II
• The spindles draw the
chromosomes to the center
plate
• The centromeres are
bound to the spindle fibers
from opposite sides
Are any sister chromatids identical? Why
or why not? Metaphase II chromosomes line up at the
“equator” of each cell
centromeres
spindle
centriole

Meiosis
Meiosis II – Anaphase II
Third phase of meiosis II
• The two sister chromatids of each chromosome are
pulled apart by the spindle fibers
• Chromosomes move away from each other toward
the poles
• The cell elongates so that the poles are farther apart
sister chromatids
separate
centromeres
pulled apart by
spindle fibers

Meiosis
Meiosis II – Telophase II
Last phase of meiosis II
• Chromosomes reach
opposite poles
• Cytokinesis (separation of
cytoplasm) occurs and
nuclear envelopes form
• Meiosis is complete with
four daughter cells
(haploid), each different
from the other and from
the parent cell
Initial
parent cell
Four haploid
daughter cells
Using these images, compare the
chromosomes in the initial parent
cell with the haploid daughter cells.

Meiosis
Summary of Meiosis
• Form of cell division that results in half the number of
chromosomes in gametes or sex cells (sperm and ova)
• Maintains the same number of chromosomes from
generation to generation
• Results in an assortment of genetic material passed on
to offspring
The numbers on the right represent how many chromosomes are found in
each human cell during meiosis.
Compare what happens to the number of chromosomes during meiosis.
46
92
parent
cell
haploid gametes (sperm or ova)
cells split
again; do
NOT
replicate!
cell
splits
DNA
replication
46
46
23
23 23 23
Meiosis I
Meiosis II
homologous
chromosomes

Think About It
Meiosis is like an
intricate dance of
chromosomes.
For each stage of
meiosis, describe
a dance move you
could do to
represent what is
happening to the
chromosomes,
and why it fits.
prophase I
metaphase I
anaphase I
telophase I
prophase II
metaphase II
anaphase II
telophase II

Mitosis and Meiosis
Comparison of Mitosis and Meiosis
Mitosis Same for Both Meiosis
Happens in body cells A type of cell division Happens in sex organs
(testes and ovaries)
One stage of division Replicates DNA Two stages of divisions
(meiosis l and ll)
Create diploid cells (2) Creates new cells Creates haploid cells (4)
New cells are genetically the
same as the parent cells
New cells are not genetically
the same as each other or
the parent cell
No genetic diversity Increases genetic diversity

Give your best answer to...
1. What are mitosis and meiosis?
2. How are mitosis and meiosis similar and different?
Check for
Understanding

Give your best answer to...
3. What occurs at different phases in cell division?
Check for
Understanding

Still have
questions?
Which essential questions do you still need help to understand?

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