Biology
Meiosis
Remember from Chapter 1:
CHARACTERISTICS OF LIVING THINGS
REPRODUCE
ALL LIVING THINGS __________
Remember from Chapter 7, there are
EUKARYOTIC
basically 2 types of cells__________
PROKARYOTIC
and ____________
Now let’s review Ch 10..........
Mitotic Cell Division
• Mitosis makes two identical
daughter cells from one Parent cell
• Bacteria and other prokaryotes
may use mitosis to reproduce –
called Binary Fission
• This is asexual reproduction
ASEXUAL REPRODUCTION
Bacteria reproduce using
BINARY FISSION
This is mitosis!
Budding is used by
plants and some animals
to reproduce asexually
(mitosis)
Hydra
Regeneration is
another way some
animals reproduce
asexually (mitosis)
Planaria
MITOSIS
identical
Produces cells that are __________
copies of parent cell
Major Events in Mitosis
• Chromosome number must be
maintained in animals.
• Many plants have more than two
copies of each chromosome.
• Mitosis and meiosis are types of
nuclear division that make
different types of cells.
• Mitosis makes more diploid cells.
MITOSIS-in conclusion
2 cells genetically
• Makes ___
identical to parent cell & to
_________
each other
2n (diploid)
• Makes _________ cells
SOMATIC (body)
• Makes __________
• Used by organisms to:
increase size of organism, repair
injuries, and replace worn out
cells
ADVANTAGES OF
ASEXUAL REPRODUCTION
Can make offspring
faster
Don’t need a partner
ADVANTAGES OF
ASEXUAL REPRODUCTION
Works great for making
new skin cells, blood
cells, and any of the
other body cells that
need to be replaced
Our body cells are called
Somatic cells (repeat word)
DISVANTAGES OF
ASEXUAL REPRODUCTION
ALL ALIKE
No genetic diversity
within a population
One disease can wipe
out whole population
Question….if not asexual,
then how can we
reproduce?
Sexual Reproduction
Sexual reproduction is when
two gametes (sex cells)
fuse together to make a
zygote.
SEXUAL REPRODUCTION
In humans, (and in many other
organisms), sexual reproduction
combines the genetic material from
the gametes of 2 parents (sperm &
egg) into a zygote
-develops into
offspring that
are genetically
DIFFERENT
__________
from parents
• Let’s review sexual reproduction
• In sexual reproduction, there are
two parents.
• Each parent has a gamete, or sex
cell to donate to the offspring.
• Each gamete has one set of
chromosomes.
• The two gametes come together
(fertilization) to form one new cell
called a Zygote.
• This Zygote will grow and divide to
become a unique organism.
ADVANTAGES OF
SEXUAL REPRODUCTION
Allows for variation in population
Individuals can be different
Provides foundation for EVOLUTION
Allow species adapt to
changes in
their environment
EGG
+
SPERM 
If egg and sperm cells had the
same number of chromosomes
as other body cells . . .
baby would have too many
chromosomes!
MEIOSIS is the way we can
avoid this problem.
Meisosis
makes cells
with half the
number of
chromosomes
for sexual
reproduction
Sex Cells (also called germ cells)
• Germ cells develop into_ gametes.
– Germ cells are located in the ovaries
and testes of humans and other animals.
egg and sperm
– Gametes are sex cells:__________.
– Gametes have DNA that is passed to
the offspring.
sex cells
(sperm)
(egg)
• Haploid (n) cells have one copy of
every chromosome.(Remember diploid
cells have two copies)
– Gametes are haploid.
– Human gametes have 22 autosomes
and 1 sex chromosome.
Haploid cells develop into mature
gametes.
• Gametogenesis is the production of
gametes.
• Gametogenesis differs between
females and males.
– Sperm become
streamlined and motile.
– Sperm primarily
contribute DNA to an
embryo.
Haploid cells develop into mature
gametes.
• Gametogenesis differs between
females and males.
– Eggs contribute DNA, cytoplasm,
and organelles to an embryo.
– During meiosis, the
egg gets most of the
contents; the other
cells form polar bodies.
KEY CONCEPT
Gametes have half the number of chromosomes
that body cells have.
DIPLOID & HAPLOID
Most cells have 2 copies of each chromosome
DIPLOID
2n
= ______________
(one from mom; one from dad)
HOMOLOGOUS
CHROMOSOMES
SOMATIC
All BODY (___________)
cells are diploid
HOMOLOGOUS Chromosomes
• SAME SIZE
• SAME SHAPE
• CARRY GENES for the
SAME TRAITS
IDENTICAL
• BUT NOT
______________!
(Don’t have to have
the
SAME CHOICES)
DIPLOID & HAPLOID
Some cells have only one copy of each
HAPLOID
1n
chromosome = _____________
Fertilization between egg and sperm
occurs in sexual reproduction.
All gametes (sperm and
egg) cells are haploid
SO……what is a chromosome?
• main organelle involved in the Cell
Cycle
• Found in the nucleus
• Contains genetic material (DNA)
• Has 2 major parts-a centromere
and sister chromatids
There are two types of Chromosomes.
• Your body cells have 23
pairs of chromosomes.
– Homologous pairs of
chromosomes have
the same structure.
– For each homologous
pair, one chromosome
comes from each
parent.
There are two types of Chromosomes.
• Chromosome pairs 1-22
are autosomes.
• Sex chromosomes, X
and Y, determine
gender in mammals.
•
•
•
•
•
•
•
•
•
•
•
•
Humans have 46 chromosomes (23 pair)
Cats have 38 chromosomes (19 pair)
Chickens have 78 chromosomes (39 pair)
Horses have 64 chromosomes (32 Pair)
Potatoes have 48 chromosomes (24 pair)
Goldfish have100 chromosomes (50 pair)
Fruit fly has 8 (4 pair)
Corn has 20 (10 pair)
Peas have 14 (7 pair)
Mosquitoes have 6 chromosomes (3 pair)
Mice have 40 chromosomes (20 pair)
Elephants have 56 chromosomes (28)
So Again……
• The zygote of humans have 23
pairs of chromosomes (or 46
individual chromosomes)
• 23 chromosomes come from each
parent
• 23 + 23 = 46
• Humans have 46 chromosomes
The process of
Meiosis- The
Formation of Sex
Cells
• Meiosis makes haploid cells from
diploid cells.
– Meiosis occurs in sex cells.
– Meiosis produces gametes.
I. Introduction to Meiosis
A. Purpose - to make sex
cells for reproduction.
B. Why can’t mitosis do
this?
Remember….mitosis would
make too many
chromosomes.
MEIOSIS
4 cells
• Makes ____
genetically different from
parent cell & from each
other
1n cells
• Makes _____
Germ cells
• Makes ______________
OR Gametes (sperm & eggs)
sexual
• Used for ____________
reproduction
WHAT MAKES MEIOSIS
DIFFERENT ?
Crossing Over, Segregation, and
Independent Assortment
ALL are ways MEIOSIS results in
GENETIC RECOMBINATION
=______________________________
different
So daughter cells are ______________
from parents and from each other
WHAT MAKES MEIOSIS
DIFFERENT ?
1. Homologous chromosomes pair up
during ________________
PROPHASE I
SYNAPSIS
= ______________
This group of FOUR (4)
chromatids is called a
TETRAD
_________________
WHAT MAKES MEIOSIS
DIFFERENT?
1. Exchange of DNA between
OVER
homologous pairs = CROSSING
_____________
during PROPHASE I
Separates gene
choices and Allows
shuffling of genetic
material
CROSSING
OVER
rearranging of DNA
• Allows for_________________
in different combinations
• After crossing over, chromatid arms
NOT IDENTICAL anymore
are________________
WHAT MAKES MEIOSIS
DIFFERENT ?
Separation during ANAPHASE I
-chromosome pairs separate
SEGREGATION &
INDEPENDENT ASSORTMENT
SEGREGATION & CROSSING OVER
together make even more combinations
INDEPENDENT ASSORTMENT
INDEPENDENT ASSORTMENT
at ANAPHASE I
Lots of different
combinations are
possible!
This is why you
don’t look exactly
like your brothers
and sisters even
though you share
the same parents!
SO WHAT MAKES MEIOSIS
DIFFERENT ?
1. SYNAPSIS & CROSSING OVER
(PROPHASE I)
2. SEGREGATION & INDEPENDENT
ASSORTMENT in Anaphase I create genetic
recombination
3. Skip INTERPHASE II (NO S) CELL
DIVIDES TWICE, BUT… ONLY COPIES
DNA ONCE
WHAT MAKES MEIOSIS
DIFFERENT ?
3. Skip INTERPHASE II (No S)
CELL DIVIDES TWICE, BUT …
ONLY COPIES ITS DNA ONCE
MITOSIS:


1
G
S
G2  P
MEIOSIS:
G1  S


M
G2  P  M
PM

A

T C
A T C (I)
 A  T  C ( II )

Workings of Meiosis
A. Meiosis is - the formation of
sex cells (eggs and sperm)
1. Gametes - another name
for sex cells.
A. Gametes have haploid
chromosome number
B. Meiosis is the making of
eggs and sperm with half
the number of
chromosomes as the parent
cell.
1. Female egg = 23
2. Male sperm = 23
C. Two Main Stages of
Meiosis
1. Meiosis I
a. Prophase I
b. Metaphase I
c. Anaphase I
d. Telophase I
2. Meiosis II
a. Prophase II
b. Metaphase II
c. Anaphase II
d. Telophase II
D. There is only one interphase
Cells go through two rounds of
division in meiosis.
• Meiosis reduces chromosome number
and creates genetic diversity.
• Meiosis I and meiosis II each have four phases,
similar to those in mitosis.
– Pairs of homologous chromosomes separate in
meiosis I.
– Homologous chromosomes are similar but not
identical.
– Sister chromatids divide in meiosis II.
– Sister chromatids are copies of the same
chromosome. homologous chromosomes
sister
sister
chromatids chromatids
• Meiosis I occurs after DNA has been
replicated.
• Meiosis I divides homologous
chromosomes in four phases.
• Meiosis II divides sister
chromatids in four phases.
• DNA is not replicated between
meiosis I and
meiosis II.
Meiosis I
A. Interphase
1. Replication of
chromosomes occurs.
2. This is the only
interphase.
B. Prophase I
1. Chromatids appear
2. Centrioles split.
3. Centrioles move to the
opposite poles.
4. Spindle fibers appear
5. Nucleolus disappears
6. Nuclear membrane
disappears
7. Tetrads form - two pairs
of homologous
chromosomes joining
together.
8. Crossing-over occurs here
- genes are exchanged
between homologous
chromsomes.
a. Creates variation in
new offspring
C. Metaphase I
1. Tetrads line up at the
equator.
D. Anaphase I
1. Tetrads separate.
2. Chromatids are pulled
to the opposite poles.
E. Telophase I
1. Chromatids still
visible.
2. Nucleolus and Nuclear
Membrane reforms.
3. Centrioles replicate
4. Two new cells.
IV. Meiosis II
A. No interphase begins this
phase.
1. 2 cells with the haploid
chromosome number begin
this stage.
2. Meiosis II will always
have two cells in each phase.
B. Prophase II
1. Nuclear membrane and
nucleolus disappear.
2. Centrioles split
3. Centrioles move to the
poles.
4. Spindle fibers form.
5. Chromatids are visible
and attach to spindle fibers.
C. Metaphase II
1. Chromatids line up on
the equator.
D. Anaphase II
1. Centromeres separate.
2. Chromotids are pulled
to opposite poles.
E. Telophase II
1. Centrioles replicate
2. Nuclear membrane
and nucleolus reappear.
3. Spindle fibers
disappear.
4. 4 new cells are formed
a. Only have half the number
of chromosomes as the parent
cell.
b. Males - all 4 remain alive
and viable.
c. Females – one egg grows
rest (polar bodies) die off.
V. Meiosis-Mitosis Comparison
A. Mitosis
1. 4 phases
2. Produces 2 diploid
cells
3. Daughter cells
identical to parent
B. Meiosis
1. 8 phases
2. 4 haploid cells produced
3. Daughter cells not
identical to parent
4. Contain tetrads and
crossing-over.
• Meiosis differs from mitosis in significant ways.
– Meiosis has two cell divisions while mitosis has one.
– In mitosis, homologous chromosomes never pair up.
– Meiosis results in haploid cells; mitosis results in
diploid cells.
Figure 11-15 Meiosis
Section 11-4
Meiosis I
Figure 11-15 Meiosis
Section 11-4
Meiosis I
Figure 11-15 Meiosis
Section 11-4
Meiosis I
Figure 11-15 Meiosis
Section 11-4
Meiosis I
Figure 11-15 Meiosis
Section 11-4
Meiosis I
Figure 11-17 Meiosis II
Section 11-4
Meiosis II
Prophase II
Metaphase II
Anaphase II
Meiosis I results in two
The chromosomes line up in a The sister chromatids
haploid (N) daughter cells,
similar way to the metaphase separate and move toward
each with half the number of stage of mitosis.
opposite ends of the cell.
chromosomes as the original.
Telophase II
Meiosis II results in four
haploid (N) daughter cells.
Figure 11-17 Meiosis II
Section 11-4
Meiosis II
Prophase II
Metaphase II
Anaphase II
Meiosis I results in two
The chromosomes line up in a The sister chromatids
haploid (N) daughter cells,
similar way to the metaphase separate and move toward
each with half the number of stage of mitosis.
opposite ends of the cell.
chromosomes as the original.
Telophase II
Meiosis II results in four
haploid (N) daughter cells.
Figure 11-17 Meiosis II
Section 11-4
Meiosis II
Prophase II
Metaphase II
Anaphase II
Meiosis I results in two
The chromosomes line up in a The sister chromatids
haploid (N) daughter cells,
similar way to the metaphase separate and move toward
each with half the number of stage of mitosis.
opposite ends of the cell.
chromosomes as the original.
Telophase II
Meiosis II results in four
haploid (N) daughter cells.
Figure 11-17 Meiosis II
Section 11-4
Meiosis II
Prophase II
Metaphase II
Anaphase II
Meiosis I results in two
The chromosomes line up in a The sister chromatids
haploid (N) daughter cells,
similar way to the metaphase separate and move toward
each with half the number of stage of mitosis.
opposite ends of the cell.
chromosomes as the original.
Telophase II
Meiosis II results in four
haploid (N) daughter cells.
Figure 11-17 Meiosis II
Section 11-4
Meiosis II
Prophase II
Metaphase II
Anaphase II
Meiosis I results in two
The chromosomes line up in a The sister chromatids
haploid (N) daughter cells,
similar way to the metaphase separate and move toward
each with half the number of stage of mitosis.
opposite ends of the cell.
chromosomes as the original.
Telophase II
Meiosis II results in four
haploid (N) daughter cells.
That’s All For Now Folks!