Lesson 2:
Chromosomes
and Mitosis
:
DNA is the chemical that gives the
cell instructions and determines
our traits. Chromosomes are
strands of DNA (look like spaghetti)
Why do cells need to divide?
• Unicellular organisms need to make more
of themselves when they get to be too
big.
• Our body cells need to divide to make
more of themselves to repair damaged
skin, bones and other body cells.
What about the chromosomes?
• After mitosis, the cell has the same number of
chromosomes as the parent. Therefore, the
daughter cells have the same DNA as the parent
cell. GENETICALLY IDENTICAL!
Below are skin cells. Talk with you
partner about why it’s important for
them to be EXACTLY the same as the
parent after they divide.
Why is it important for cells to be
exactly the same as the parent after
mitosis?
So that they can have the same exact
structure and perform the same exact
function of the old skin cells.
Below is a picture of cell going through the
process of mitosis. Talk with your partner
about the questions below:
Is this sexual or asexual reproduction?
The black strands inside of the cell are
called _______________
There is ______ parent cell.
At the end of mitosis, there are _____
daughter cells, or offspring.
A tiger’s normal body cells have 38 chromosomes.
• Pretend the tiger got bit by an alligator and the bite
broke its skin.
• How many chromosomes are in the parent skin
cell?
• What process will the tiger’s cell go through to
make more skin cells to repair the wound?
• What form of reproduction is this?
• Why?
• How many chromosomes will the new daughter
skin cells have?
The alligator bite also tore some muscle
• What process will the tiger’s muscle cell go through
to repair itself?
• What form of reproduction is this?
• Why?
• How many chromosomes will the new muscle cell
have?
A bacteria living in the lake with the
alligator is getting too big and must split
into two to carry on its life processes.
• Is this sexual or asexual reproduction?
• What process will the bacteria go through to make
two new bacteria?
• Pretend the parent bacteria had 1 chromosome,
how many will the 2 new bacteria cells have?
Here is a cell from your body:
• After mitosis, draw what the two daughter cells
should look like:
Which method (A or B) is showing asexual
reproduction? ______
Describe the number of chromosomes in
the daughter cells in Method A.
KP #2: How do chromosomes exist
in our normal body cells?
They exist in
pairs. (2)
A pair of
chromsomes is
called
HOMOLOGOUS
chromosomes.
KP #3: Why do they come in pairs?
One comes
from MOM
One comes
from DAD
KP #4:
How many
chromosomes do
humans have in
our normal body
cells?
46!