Meiosis
Chapter 10.1 and 11.3
Do Now
How is a baby made?
 On the cellular level, draw how a baby is
made. (NO PHALLIC SYMBOLS
PLEASE!)

Why does sex exist?

Sexual reproduction creates genetic
variability
Let’s Brainstorm…

How do we get our different traits?
What is the difference between
fraternal and identical twins?
Do Now
What is mitosis?
 What is meiosis?
 List 2 differences between the two?

Let’s define the following
words…

Meiosis:
 Sexual

Gamete:
 Sex

reproduction-production of gametes
Cells (egg and sperm) haploid
Somatic Cells:
 Body
Cells - diploid

Haploid:
 Half
the chromosome number (n)
 1 of each pair of chromosomes (23)

Diploid:
2
of each type of chromosome (2n)
 Twice the haploid number

Fertilization:
 Sperm

enters egg
Zygote:
 Fertilized
egg (diploid)
Chromosomes and Chromosome
Number
 Human body cells have 46 chromosomes
 Each parent contributes 23 chromosomes
 Homologous chromosomes —one of
two paired chromosomes, one from each
parent
Karyotype
Homologous Chromosomes
 Same length
 Same centromere position
 Carry genes that control
the same inherited traits
Meiosis
The sexual life cycle
in animals involves
meiosis
 Meiosis produces
gametes.
 When gametes
combine in
fertilization, the
number of
chromosomes is
restored.

Cell Cycle
DNA
Replication
Prepare
Growth
Division
2N
2N
Mitosis
N
N
N
N
Meiosis
2N
Do Now

Label A, B, and C

(Hint same size, same
shape…)
Meiosis

2 Division
 Meiosis
I (separation of homologous
chromosomes)
 Meiosis II (separation of sister chromatids)
Interphase
Same as Mitosis (G1, S, G2)
 DNA- Chromatin
 Centrioles- located near the nucleus

Prophase I
Pairing of homologous chromosomes
occurs. (Synapsis)
 Each chromosome consists of two
chromatids.
 The nuclear envelope breaks down.
 Spindles form

Prophase I (cont.)
Crossing over produces exchange
of genetic information.
 Crossing over —chromosomal
segments are exchanged between
a pair of homologous
chromosomes.

Metaphase I
Chromosome centromeres attach to
spindle fibers
 Homologous chromosomes line up at the
equator.

Anaphase I

Homologous chromosomes separate and
move to opposite poles
Telophase I
The spindles break down.
 Chromosomes uncoil and form two nuclei.
 The cell divides.

Prophase II

A second set of phases begins as the
spindle apparatus forms and the
chromosomes condense.
Metaphase II
A haploid number of chromosomes line of
at the equator
 Sister chromatids line up

Anaphase II
The sister chromatids are pulled
apart at the centromere by spindle
fibers
 Move toward the opposite poles of
the cell.

Telophase II
The chromosomes reach the poles, and the
nuclear membrane and nuclei reform.
Cytokinesis
 Cytokinesis results in four haploid cells
 Each with n number of chromosomes.
Animation

http://www.cellsalive.com/meiosis.htm
Animations on Meiosis

http://highered.mcgrawhill.com/sites/0072437316/student_view0/
chapter12/animations.html#
Do Now: Label the phases of meiosis
Genetic Variability
Depending on how the
chromosomes line up at the
equator, four gametes with
four different combinations of
chromosomes can result
(independent assortment).
 Genetic variation also is
produced during crossing
over
 Random fertilization.

Genetic Variability Animation

http://highered.mcgrawhill.com/sites/0072437316/student_view0/
chapter12/animations.html#
Review Spermatogenesis and oogenesis

Think – Pair - Share
Draw out the stages of meiosis using the
following cell. Make sure you draw the cell with
crossing over of only one pair of homologous
chromosomes! (use colored pencils)
Do Now – Period 3
How many
autosomes?
 How many sex
chromosomes?
 What is the sex of
this patient?
 Monosomy,
Trisomy?
 Is this individual
normal?


Do Now
Match the description to the phase of meiosis.
1. Sister Chromatids are pulled
A. Prophase I
apart. _____
2. Homologous chromosomes line
B. Metaphase I
up in the middle of the cell._____
3. 2 daughter cells are formed ____ C. Telophase I
4. Nuclear membrane disappears__ D. Anaphase II
5. Nuclear membrane reforms
around 4 cells ____
6. Homologous chromosomes are
pulled apart ____
E. Anaphase I
F. Telophase II
Review

How does meiosis promote genetic
variability? List 3 reasons why.
THINK – PAIR - SHARE

If a hamster has 44 chromosomes in G1
phase of the cell cycle, then…
 How
many chromatids are in G2 Phase?
 How many chromosomes are in the G2
Phase?
 How many chromosomes will be in each cell
after it has gone through mitosis?
Do Now
What two divisions do your cells undergo?
 What are the differences between the
two?
