Meiosis

Catalyst:
What
type of cells does mitosis occur
in?
Somatic cells are 2N. What does this
mean?
Why is it important that cells copy all
their DNA during mitosis, and become
Write in complete sentences!
4N?
Don’t talk during the Catalyst!
Agenda






Catalyst
Catalyst Review
Meiosis
BRAIN GAIN
Comparing meiosis to mitosis
EQ
HOMEWORK: Finish Mitosis vs. Meiosis sheet
Study for Cellular Processes unit test tomorrow!
(ATP, Photosynthesis, Cellular Respiration, Mitosis, Meiosis)
Meiosis Review

What type of cells does mitosis occur in?
 Mitosis

occurs in somatic cells.
Somatic cells are 2N. What does this mean?
 2N
means there are two of each type of
chromosome.

Why is it important that cells copy all their DNA
during mitosis, and become 4N?
 It
is important that cells copy all their DNA during
mitosis and become 4N because the cell splits in
half. When the parent cell splits in half, the
daughter cells will still have 2N, an exact copy of
the parent cell.
Objectives
By the end of today, SWBAT…
State the purpose of meiosis
Compare mitosis and meiosis
Review of Mitosis

Somatic cells have 2 of each type of
chromosome
 Mitosis
produces cells that are 2N.
2N→4N
2N
2N
Review of Mitosis
But wait…
There’s another type of cell division
for one specific purpose!
Meiosis

Key Point #1: Meiosis is cell division
for gametes.
Gametes
= sex cells
Eggs for women, Sperm for men
Meiosis is for sexual reproduction
New Vocabulary

Somatic cells have 2 of each type of chromosome
(2N). This means that somatic cells have all the
instructions necessary to make an organism.
 Another
word for 2N is diploid.
Somatic cells are
diploid.

Gametes only have 1 of each type of chromosome
(1N). This means that they only have HALF of the
DNA necessary to make an organism.

Another word for 1N is haploid.
haploid.
Gametes are
Now does it
make sense
why you
need one
sperm and
one egg??
Why?

Key Point #2: Gametes must be haploid (1N)
 Every
human must have two copies of each chromosome
 If gametes were diploid (2N), the child would not
survive
2N
2N
4N
2NYou
is the
regular
don’t
want
number
of
a
baby with
chromosomes!
4N!!!!!!
1N
2N
1N
So how does this work?

In meiosis, there are two rounds of cell division
MEIOSIS I
MEIOSIS II
1N
2N→4N
2N
1N
1N
2N
1N
So how does this work?

In meiosis, there are two
rounds of cell division
2N
4N
MEIOSIS I
2N
2N
MEIOSIS II
1N 1N
1N 1N
Family Matters

Meiosis can explain a lot of things in
life…
 Why
am so much better looking than my
brother, even though we have the same
parents?
Thank you, meiosis!
NOT IDENTICAL

Key Point #3: Meiosis produces
genetically DIFFERENT cells.
 Why
different? Genetic information between
chromosomes gets switched.
Germ Cell
More Meiosis
A Closer Look
1N
2N
1N
1N
1N
Hold Up
Check Our Understanding….
What is mitosis is for?
 What is meiosis is for?
 What’s the difference between haploid
and diploid?
 Why is it important that gametes are
haploid?

Guided Practice
Meiosis produces…
a) Identical cells
b) Different cells
c) 23 types of cells
d) Two copies of each cell
Guided Practice
Meiosis occurs in…
a) Somatic cells
b) Gametes
c) Chromosomes
d) All eukyarotic cells
Guided Practice
How many times do cells divide
in meiosis?
a) 1
b) 2
c) 3
d) 4
Guided Practice
The cells produced by meiosis are
_____, also known as ______.
a) Haploid… 1N
b) Diploid… 1N
c) Haploid… 2N
d) Diploid… 2N
Guided Practice
Gametes have _____ copy/copies
of each type of chromosome.
a) 1
b) 2
c) 23
d) 46
Guided Practice
What would happen if gametes were
2N?
a) Children would be 2N, and die
b) Children would be 4N, and have
superpowers
c) Children would be 4N, and die
d) Trick question, gametes are 2N!
Were You Paying Attention?
I’m going to ask the same
questions again!
Answers are scrambled…
Guided Practice
Meiosis produces…
a) Different cells
b) Two copies of each cell
c) Identical cells
d) 23 types of cells
Guided Practice
Meiosis occurs in…
a) Chromosomes
b) Somatic cells
c) All eukyarotic cells
d) Gametes
Guided Practice
How many times do cells divide
in meiosis?
a) 4
b) 3
c) 2
d) 1
Guided Practice
The cells produced by meiosis are
_____, also known as ______.
a) Haploid… 1N
b) Haploid… 2N
c) Diploid… 1N
d) Diploid… 2N
Guided Practice
Gametes have _____ copy/copies
of each type of chromosome.
a) 2
b) 46
c) 23
d) 1
Guided Practice
What would happen if gametes were 2N?
a) Children would be 4N, and die
b) Children would be 4N, and have
superpowers
c) Trick question, gametes are 2N!
d) Children would be 2N, and die
Step Yo’ Game Up!
So far, we’ve only been
talking about meiosis
But we need to be able to
COMPARE meiosis and
mitosis

Put in your notes….YOU TRY 2 MINS
MITOSIS
SOMATIC OR
GAMETES?
HAPLOID OR
DIPLOID?
2N OR 1N?
IDENTICAL CELLS OR
DIFFERENT CELLS?
1 OR 2 DIVISIONS?
MEIOSIS
ANSWERS
MITOSIS
MEIOSIS
somatic
gametes
diploid
haploid
2N OR 1N?
2N
1N
IDENTICAL CELLS OR
DIFFERENT CELLS?
identical
different
1 OR 2 DIVISIONS?
1 division
2 divisions
SOMATIC OR
GAMETES?
HAPLOID OR
DIPLOID?
Guided Practice
Produces cells with 2N
chromosomes
Mitosis
b) Meiosis
a)
Guided Practice
Creates diploid cells
Mitosis
b) Meiosis
a)
Guided Practice
Produces four DIFFERENT
daughter cells
Mitosis
b) Meiosis
a)
Guided Practice
Creates cells with 1N
chromosomes
Mitosis
b) Meiosis
a)
Guided Practice
Genetic information between
chromosomes gets switched
Mitosis
b) Meiosis
a)
Guided Practice
Which of the following is true?
A) There are more cell divisions in mitosis
than meiosis
B) There are more cell divisions in meiosis
than mitosis
C) There are the same number of cell
divisions in both
D) The cell does not divide in mitosis or
meiosis
Guided Practice
Mitosis occurs in _____, meiosis occurs
in _____
a) Animals… Animals and plants
b) Gametes… somatic cells
c) Eukaryotic cells… prokaryotic cells
d) Somatic cells… gametes
Guided Practice
Mitosis produces _____ cells,
meiosis produces _____ cells.
a) Haploid… diploid
b) Gametes… somatic
c) Eukaryotic… prokaryotic
d) 1N… 2N
Work it out.

Meiosis section.
 We


have LIMITED TIME. Use your time WISELY.
Mitosis vs. Meiosis worksheet (Last page of your
packet)
If you are having trouble, NOW is the
time to get help. We have a UNIT TEST
tomorrow.
Exit Questions
What is the purpose of meiosis?
 How many cells does meiosis produce?
 Use your knowledge of meiosis to
explain why Ms. S so much better
looking than her brother. (Hint: it has to
do with sperm and egg cells.)

Write in complete sentences!
Don’t talk during the Catalyst!