SU:

Vocabulary for cell division (Mitosis)
Define each word and then use the word in a
complete sentence. Use pp 244-248
 Mitosis
 Cytokinesis
 Interphase
 Prophase
 Metaphase
 Anaphase
 Telophase
Cell Division
Chapter 10 Section 2
Chapter 11 Section 4
What’s a gene?
Process of Making a Chromosome
Chromosome
Nucleosome
DNA
double
helix
Coils
Supercoils
Histones
Chromatin – DNA tightly coiled around proteins called Histones
Nucleosome – beadlike structure made of chromatin
Supercoils – nucleosomes packed together
GoChromosome
to
Section:
– tightly packed supercoils
Chromosomes

Made of DNA and Histones (protein)

Function :
- passes genetic info. from 1 generation to the next

Genes- located on chromosomes
- information about traits are located here

Traits – characteristics passed on by your parents
Chromosomes Numbers

Every organism has a specific # of
chromosomes
 Humans

=
46 chromosomes
The # of chromosomes DOES NOT indicate
the COMPLEXITY of an organism
Example – a goldfish has 124 chromosomes
Structure of Chromosomes

Each chromosome consists of:
* CHROMATIDS – identical parts
- called “sister chromatids”
* CENTROMERE – point at which each
chromatid are attached to each other
chromatid
centromere
Structure of Chromosomes (cont.)
the cell divides into 2 new cells –
the “sister chromatids” separate and
each one goes into a new cell
 When
 Each
chromosome consists a pair
of chromatids (2)
 Humans = 46 chromosomes
= 92 chromatids
Chromosome Quiz
1.
2.
3.
4.
5.
Name the 2 substances that make up
chromosomes. (2 points)
How many chromosomes do humans
have? (1 point)
What is the function of chromosomes?
(1 point)
At what point are chromosomes visible in
the nucleus? Why? (2 points)
Draw and label a chromosome. (4 points)
SU: Meiosis


Copy and Answer both questions. You may use your
textbook, Section 11-4
What process produces gametes?
 Mitosis
 Meiosis
 Fertilization
 Chromosome

replication
Haploid cells are cells that have
 One
chromosome of each type
 Two chromosomes of each type
 Pairs of homologous chromosomes
 Two sets of chromosomes
Classroom Business
Meiosis Quiz on Thursday
 Closed Book
 Top scorer in each class gets +5
 Have your completed Genetics Packet on
Thursday! This is worth 50 points. If you
do not have one, you will have to spend a
lot of time copying the information.

Cell Cycle
The series of events that cells go through as
they grow and divide.
 During this cycle the cell:
1. grows
2. prepares for division
3. divides to form 2 “daughter”
(identical) cells
Then each daughter cell prepares to
begin the cycle again

Events of the Cell Cycle
Cell Cycle
includes
G1 phase
Go to
Section:
Interphase
M phase
(Mitosis)
is divided into
is divided into
S phase
G2 phase
Prophase
Metaphase
Anaphase
Telophase
Interphase

Longest phase of the cell cycle

Known as the “in-between” period of growth

Divided into 3 Phases: G1, S, and G2
G1 (Gap 1) Phase

Cells do most of their growing during this
phase

Cells increase in size

Manufacturing of new proteins & organelles
S (Synthesis) Phase

DNA is replicated

Synthesis of DNA molecules & Histones occur
G2 (Gap 2) Phase

Shortest of the phases

Organelles & molecules needed for cell
division are produced

When this phase is complete, cells are ready
for the M Phase (mitosis) and begin the
process of cell division
Mitosis

The 1st stage of cell division in eukaryotic cells

Depending on type of cell, this phase can last
from a few minutes to several days.

Divided into 4 phases
Prophase





The 1st & longest phase of
Mitosis
(50 – 60%of whole process)
A. Chromatin condense to form
chromosomes
B. Centrioles separate and
move to opposite sides of the
nucleus
C. structures called SPINDLES
begin to form – they help to
separate chromosomes
D. Nucleolus disappears &
nuclear envelope breaks down
Metaphase

Often last only a few
minutes

Chromosomes line up
across the center of
the cell

Each chromosome is
connected to a spindle
fiber at its centromere
Anaphase

The spindle fibers pull
apart the sister chromatids

Each chromatid becomes
its own chromosome
and move towards the
centrioles at opposite ends
of the cell

The phase ends when the
chromosomes reach the
centrioles & stop moving
Telophase

Chromosomes lose their
distinct shapes

Nuclear envelope re-forms
around each group of
chromosomes

Spindle fibers disappear & a
nucleolus becomes visible in
each new nucleus

Mitosis is complete, but cell
division is not
Cytokinesis

Cytoplasm pinches in half

Each daughter cell has an
identical set of chromosomes
from the parent cell

Usually occurs at the same
time as telophase

Cell division is not complete
until cytokinesis is complete
Overview of Mitosis
SU: Identification of P.M.A.T.
 Pick
up the handout in the front of
the room and match the picture to
the step in mitosis.

These pictures are of cells in the root of an onion
plant and the show one of the major phases in
cell division. (Interphase, Prophase, Metaphase,
Anaphase, or Telophase)
Today’s Assignment




Objective: Create a study guide for meiosis.
Step 1: Take a clean piece of paper and fold it
in half three times so that you have 8 squares.
Step 2: Turn to page 276-277
Step 3: Turn the paper horizontal and label
each box left to right, top to bottom.
Prophase I
Metaphase I Anaphase I
Telophase I
Cytokinesis
Prophase II
Metaphase II Anaphase II
Telophase II
Cytokinesis
SU: Meiosis (copy and answer)

What is the outcome of meiosis II
 Four
diploid cells
 Two diploid cells
 Two haploid cells
 Four haploid cells

All cells that divide by meiosis are
 Haploid
cells
 Called oogonia
 Called Spermatogonia
 Found in reproductive organs
Asexual Reproduction
This bud’s for you!
Hydra
Homologous
chromosomes
Cell Cycle Quiz
Label each picture with the correct phase of
mitosis
A
B
D
C
Label each picture with the correct phase of
mitosis or meiosis.
A
B
D
C
Homologous Chromosomes


Chromosomes that
are in all sexually
reproducing
organisms
Occur in pairs
2 identical chromosomes
= homologous
chromosomes


same size and shape.
are different than all
other chromosomes
Diploid Cells

Diploid Cells – contain both chromosomes of
a homologous pair
Human cell = 23 pairs of homologous
chromosomes
2 x 23 = 46
Human Chromosome # = 46
Haploid Cells

Haploid Cells – contain only 1 chromosome
of a homologous pair
23 pairs of homologous chromosomes
1 x 23 = 23
**all egg & sperm cells = 23 chromosomes
ALSO KNOWN AS GAMETES
(egg)23 + (sperm) 23 = 46 chromosomes – human baby

Zygote – a new cell formed by a sperm & egg cell
- has the normal number of chromosomes
MEIOSIS

The process of reducing the number of
chromosomes per cell in half

Separating homologous chromosomes in
a diploid cell

Making a diploid (46) into a haploid (23)
Process of Meiosis

Involves 2 distinct divisions:
Meiosis I
Meiosis II

Begin with 1 diploid cell (46)

End with 4 haploid cells (23)
Meiosis I

Looks like MITOSIS

But in Meiosis I, each chromosome is paired
with it corresponding HOMOLOGOUS
CHROMOSOME

This forms a TETRAD – 4 chromatids
( 2 from each chromosome)
Crossing Over
TETRAD
•When homologous chromosomes pair up to make
tetrads – they exchange portions of their chromatids
•This is called CROSSING OVER
•This results in the exchange of genes between the
homologous chromosomes
•This produces new combinations of genes
RESULTS OF MEIOSIS I
The chromosomes go through the same
phases as Mitosis
 Produces 2 new cells with 46 chromosomes
each
BUT ………………..
1. the new “daughter” cells DO NOT have
identical sets of chromosomes like the parent

2. are different from each
- because of crossing over & the separation
of the homologous chromosomes
Meiosis II

The 2 cells from Meiosis I enter this
2nd division

Unlike Meiosis I – the 2 cells …..
do not replicate the chromosomes

The cells go through each phase just like in
Meiosis I
Results of Meiosis II

4 daughter cells that are haploid cells

Have only half of the # of chromosomes

All are different from each other

All are different from its parent cell
Gamete Formation
The making of reproductive cells
 MALE GAMETE = SPERM CELLS


Through meiosis – males produce 4 new
sperm cells

FEMALE GAMETE = EGG CELLS (OVUM)

Through meiosis – females produce only 1
egg cell and 3 polar bodies (incomplete)