Meiosis
Question of the Day
3-14
How is meiosis different
from mitosis (there is more
than one correct answer)?
IMPORTANT ANNOUNCEMENT
3-14
PEROIDS 1 & 2: Monday
March 14, Tuesday March 15, and
Wednesday March 16 class is in
mod # 1.
Bring study hall type work / reading for
second half of class.
Announcement
Plan for the Unit # 6 Test
at the end of next week
3-14
(Thursday 3-17 or Friday 3-18)
Reviewing Objectives

Describe the structure of a chromosome.

How is a prokaryotic chromosome different than
a eukaryotic chromosome?

Compare the numbers of chromosomes in
different species.

Explain the differences between sex
chromosomes and autosomes.

How are diploid and haploid cells different?
Reviewing Objectives

Describe the events of cell division in
prokaryotes.

Name the two parts of the cell that are equally
divided during cell division in eukaryotes.

Summarize the events of interphase.

Describe the stages of mitosis.

Compare cytokinesis in animal cells with
cytokinesis in plant cells.

Explain how cell division is controlled.
Meiosis I:
 crossing
over takes place
 homologous
chromosomes
get separated
 2 new haploid
cells result
Meiosis II:
 sister
chromatids
get separated
(like in
mitosis)
 2 new
haploid cells
result from each
of the cells from
meiosis I (total
4 new cells)
During meiosis…

Synapsis – pairing of homologous
chromosomes during prophase I – this
did not occur in mitosis

Tetrad –
 Each pair of homologous chromosomes
Formation of Haploid Cells

Crossing-over – when portions of homologous
chromosomes exchange genetic material
 Occurs during prophase I
and results in genetic
recombination.

Genetic recombination –
 Regrouping of genes in an offspring that
results in a genetic makeup that is different
from the parents
Crossing Over
Crossing Over
Why is genetic recombination important?
Genetic recombination is the key to
sexual reproduction.
Why is genetic recombination important?

Asexual Reproduction = genes identical to
parents
 PRO:
 Offspring
well adapted to survival
 Need only one parent
 CON:
 If susceptible to a disease, may kill off
the entire population (b/c all genes are
the same)
Why is genetic recombination important?

Sexual Reproduction
 PRO:
 Leads to genetic diversity from parents
 Not all members will die from a disease
(leads to specie evolution)
 CON:
 Need two parents
3-14
Topics:
The S-phase of Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
The chromosome
Creativity
Slogan / Title
MAKE SURE YOU
Aesthetically pleasing
GET A CHECKLIST
Accurately descriptive
FOR YOUR TOPIC!!! and understandable
3-15
1. During meiosis ________ are
separated during meiosis I and ________
are separated during meiosis II.
Announcement
Plan for the Unit # 6 Test
Friday 3-18
3-15

Nondisjunction
- when
a set of homologous
Error
in Meiosis
chromosomes do not separate during
metaphase
 Means "not coming apart"
 Results in gametes with incorrect
chromosome #
Error in Meiosis

Trisomy = 3 chromosomes
Monosomy = only 1
chromosome
Results
 If fertilization occurs, fetus will
probably die
 Down Syndrome – trisomy 21
 Edwards syndrome trisomy 18
 Turners Syndrome – monosomy X
 Triple-X syndrome – trisomy X
 Klinefelters Syndrome - XXY
Sex Chromosome Abnormalities
Female
Male
Syndrome
Syndrome
Genotype
Genotype
XX
normal
XY
normal
XO
Turner
XXY
Klinefelter
XXX
Triple-X
XYY
XYY

Independent Assortment – random
separation of homologous
chromosomes during anaphase I
 Results in genetic variation
How does meiosis ensure genetic
variation?
Independent assortment –
 homologous chromosomes separate
randomly
 Means sperm or egg will randomly
receive various alleles for genes
 Crossing over –
 chromosomes that are donated to the
offspring are different from the parents

Crossing over
Independent
assortment
Definition (not the equation): Name each step.
Why does it occur?
mitosis
One identifying
characteristic of each step:
result of mitosis
(How many cells? What
kind?) =
Definition (not the equation): 2 ways different from
mitosis
What does it make?
meiosis
Crossing over =
Independent assortment =
Nondisjunction =
result of
meiosis (How many cells?
What kind?) =
In autosomal cells
Development of Gametes

Spermatogenesis 

Oogenesis –


is the process by which sperm cells are produced.
is the process that produces mature egg cells.
Polar Bodies –
Three other products of oogenesis
 Eventually break down – only one egg produced
 One egg gets majority of cytoplasm


Read book pages 161-164
Answer questions #1, #3, #4 - #6, #8, #9
 If you do not get done in class it is homework. If you are
going to use the online book, you must write the question
down before you leave. Or just borrow a book (but you
must let me know)

Meiosis in Male and Female
Animals
Sexual Reproduction

Sexual reproduction –



is the formation of offspring through meiosis
and the union of a sperm and an egg.
Offspring produced by sexual reproduction
are genetically different from the parents.
Why?

½ genes from different parent
 b/c of crossing over, chromosomes received
are different from parent’s original
 Independent assortment
The End
3-25 Practice Quiz

Direction: Get a piece of paper and answer the
following questions. No talking, pretend this is
a real quiz…
1.
2.
3.
4.
5.
6.
7.
8.
9.
What are autosomes?
If a cell is diploid, and the haploid number is 10, how
many chromosomes does it have?
Which of YOUR cells are diploid?
Which of YOUR cells are haploid?
What are gametes? Give an example
What are the products of mitosis? How many
chromosomes are in humans?
What are the products of meiosis? How many
chromosomes do they have?
Why is genetic variation important in a population?
What are the products of spermatogenesis? What are
the products of oogenesis?
10.
11.
12.
13.
What is nondisjunction?
How many chromosomes does a haploid cell
have in a horse if its chromosome count is 64?
What are homologous chromosomes?
What are some differences between mitosis
and meiosis?
Chapter 8
Standardized Test Prep
Multiple Choice
1. Which of the following statements about
prokaryotic chromosomes is true?
A. Prokaryotes have at least two chromosomes.
B. Prokaryotic chromosomes consist of a
circular DNA molecule.
C. Prokaryotic chromosomes include histone
and nonhistone proteins.
D. Prokaryotic chromosomes are made of DNA
wrapped tightly around histone proteins.
Chapter 8
Standardized Test Prep
Multiple Choice, continued
1. Which of the following statements about
prokaryotic chromosomes is true?
A. Prokaryotes have at least two chromosomes.
B. Prokaryotic chromosomes consist of a
circular DNA molecule.
C. Prokaryotic chromosomes include histone
and nonhistone proteins.
D. Prokaryotic chromosomes are made of DNA
wrapped tightly around histone proteins.
Chapter 8
Standardized Test Prep
Multiple Choice, continued
2. Crossing-over occurs during which process?
F. mitosis
G. meiosis I
H. meiosis II
J. interphase
Chapter 8
Standardized Test Prep
Multiple Choice, continued
2. Crossing-over occurs during which process?
F. mitosis
G. meiosis I
H. meiosis II
J. interphase
Chapter 8
Standardized Test Prep
Multiple Choice,
The graph below shows
continued
3.
In
which
phase
of
mitosis
the relative mass of DNA and
chromosome number
for a cell undergoing mitosis.
Use the graph to answer
the questions that follow.
do chromatids separate
and become individual
chromosomes?
A. prophase
B. metaphase
C. anaphase
D. telophase/cytokinesis
Chapter 8
Standardized Test Prep
Multiple Choice,
The graph below shows
continued
3.
In
which
phase
of
mitosis
the relative mass of DNA and
chromosome number
for a cell undergoing mitosis.
Use the graph to answer
the questions that follow.
do chromatids separate
and become individual
chromosomes?
A. prophase
B. metaphase
C. anaphase
D. telophase/cytokinesis
Chapter 8
Standardized Test Prep
Multiple Choice,
The graph below shows
continued
4.
What
process
occurs
that
the relative mass of DNA and
chromosome number
for a cell undergoing mitosis.
Use the graph to answer
the questions that follow.
leads to the decrease in the
cell’s DNA mass?
F. prophase
G. metaphase
H. anaphase
J. telophase/cytokinesis
Chapter 8
Standardized Test Prep
Multiple Choice, continued
The graph below shows
the relative mass of DNA and
chromosome number
for a cell undergoing mitosis.
Use the graph to answer
the questions that follow.
4. What process occurs that
leads to the decrease in the
cell’s DNA mass?
F. prophase
G. metaphase
H. anaphase
J. telophase/cytokinesis
Chapter 8
Standardized Test Prep
Multiple Choice,
continued
5. prokaryote : binary fission :: eukaryote :
A. mitosis
B. cytokinesis
C. crossing-over
D. genetic recombination
Chapter 8
Standardized Test Prep
Multiple Choice,
continued
5. prokaryote : binary fission :: eukaryote :
A. mitosis
B. cytokinesis
C. crossing-over
D. genetic recombination
Chapter 8
Standardized Test Prep
Multiple Choice,
continued
The diagram below
shows a model of cell
division. Use the diagram to
answer the question that
follows.
6. Which type of cell division
is shown in the diagram?
F. mitosis
G. meiosis
H. binary fission
J. sexual reproduction
Chapter 8
Standardized Test Prep
Multiple Choice,
continued
The diagram below
shows a model of cell
division. Use the diagram to
answer the question that
follows.
6. Which type of cell division
is shown in the diagram?
F. mitosis
G. meiosis
H. binary fission
J. sexual reproduction
Chapter 8
Standardized Test Prep
Short Response
Human cells are either diploid or haploid. All
human cells with 46 chromosomes are
diploid.
Would a human cell with any 23
chromosomes be
haploid? Explain your answer.
Chapter 8
Standardized Test Prep
Short Response,
continued
Human cells are either diploid or haploid. All human
cells with 46 chromosomes are diploid.
Would a human cell with any 23 chromosomes be
haploid? Explain your answer.
Answer:
No, a haploid cell has one complete set of
chromosomes, which in the case of humans is 23.
Randomly having 23 chromosomes would not be
considered haploid.
Chapter 8
Standardized Test Prep
Extended Response
For a cell to function efficiently, its surface area must
exceed that of its volume.
Part A Explain how cell division maintains the
relationship between surface area and volume.
Part B How does a stable ratio between surface
area and volume help maintain proper cell
functioning?
Chapter 8
Extended Response, continued
Answer:
Part A The smaller the cell, the greater is the
ratio of surface area to volume. Cell division
makes one larger cell into two smaller cells.
Part B By having a stable ratio between surface
area and volume, cells are able to maintain
homeostasis by taking in and getting rid of
substances efficiently through osmosis and
diffusion.
Stages of Mitosis