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Meiosis

Catalyst:
How
many DIFFERENT TYPES of
chromosomes do human somatic cells
have?
How many COPIES OF EACH TYPE of
chromosome do human somatic cells
have?
Write in complete sentences!
Don’t talk during the Catalyst!
Objectives
By the end of today, SWBAT…
Describe the phases and
products of meiosis
Let’s look at Mitosis one more time.
Review and Vocabulary

Human cells have 23 different types of
chromosome
 Mitosis
produces cells that are 2N. Another
word for this is diploid.
 Diploid
= 2 copies of each type of chromosome
 Meiosis
produces cells that are 1N. Another
word for this is haploid.
 Haploid
= 1 copy of each type of chromosome
Why?

Key Point #1: 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
N
Meiosis
Meiosis is the process of gamete
cell division. It is used for
sexual reproduction.
Key Point #2: In meiosis,
gametes divide twice.
Produces
four cells
Each cell is haploid (1N)
Meiosis

In meiosis, there are two rounds of cell division
MEIOSIS I
MEIOSIS II
1N
2N→4N
2N
1N
1N
2N
1N
Family Matters

Meiosis can explain a lot of things in
life…
 Especially
 Why
the age-old question…
am I look so much better looking than my
sister, even though we have the same parents?
Thank you, meiosis!
Meiosis

Key Point #3: Meiosis produces genetically
DIFFERENT cells.
 Why
different? Genetic information between
chromosomes gets switched.
Germ Cell in
Interphase
Prophase
I
Metaphase
I
Anaphase
I
Telophase I
More Meiosis
Prophase
II
Metaphase
II
Anaphase
II
Telophase
II
A Closer Look
1N
4N
1N
1N
1N
Take a step back
Can someone tell me what mitosis is for?
 Can someone tell me what meiosis is for?
 What’s the difference between haploid
and diploid?
 Why is it important that gametes are
haploid?

ActivExpression Practice!
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
On the test, you will have
to COMPARE meiosis and
mitosis

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
Independent Practice/HW
Key Point Wrap-Up
Key Point #1: Gametes must be haploid
(1N)
 Meiosis is the process of gamete cell
division. It is used for sexual
reproduction.
 Key Point #2: In meiosis, gametes
divide twice.
 Key Point #3: Meiosis produces
genetically DIFFERENT cells.

Exit Questions
What is the purpose of meiosis?
 How many cells does meiosis produce?
 Why is Mr. J so much better looking than
his sister? (Hint: it has to do with sperm
and egg cells.)

Write in complete sentences!
Don’t talk during the Catalyst!
The following slides are extension
Will not be tested; only if students are
curious
Women only produce one
viable egg in meiosis, the
other three cells are polar
bodies that will be
destroyed.
Women only produce a few
hundred eggs over the
course of their entire lives.
Oogenesis
Men are busy – meiosis
produces roughly
250,000,000 sperm per
day!!!
Spermatogenesis