CELL CYCLE AND CELL DIVISION ACTIVITY
a. When you fall and scrape the skin of your hands or knees how does your
body make new skin cells to replace the skin cells that were scraped off?
b. How does each new cell get a complete set of chromosomes?
c. Each of us began as a single cell: How did that single cell develop into a
body with more than a trillion cells?
I.
Chromosomes and Genes
Each chromosome contains a long molecule of DNA. This molecule of DNA contains
many genes. A gene is a segment of the DNA molecule that gives the instructions for
making a protein. For example, one gene gives the instructions for making a protein
enzyme, which helps to make the pigment melanin, a molecule that contributes to
our skin and hair color.
Each cell in your body has two copies of each chromosome. These two copies are
called a pair of homologous chromosomes. The DNA in both homologous
chromosomes contains the same genes at the same locations in the chromosome.
However, the two homologous chromosomes may have different versions of a gene.
Different versions of the same gene are called alleles. Different alleles give the
instructions for making different versions of the protein, and different versions of
the protein can result in different characteristics (see examples in the following
table).
Allele
A
a
R
r
S
s
Protein
 Normal enzyme for
melanin production
 Defective enzyme
for melanin
production
If both homologous chromosomes
have this allele, the person has:
 Normal skin and hair color
 Very pale skin and hair color (albino)
 Normal protein that 
responds to an odor
 Protein that does not 
respond to the odor
 Normal hemoglobin
 Sickle cell
hemoglobin
Can smell that odor
Can not smell that odor
 Normal blood
 Sickle cell anemia (sickle shaped red blood
cells that can block blood flow, causing pain
and other problems)
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Questions:
1.
2.
3.
4.
5.
List everything in the above table that is part of a DNA molecule.
How many different genes are listed in the table above?
How many total alleles are listed in table above?
How many alleles are listed for each gene?
How many chromosomes are described in table above?
6. The following diagram illustrates just three of the many alleles on a pair of
homologous chromosomes in a girl named Tiffany.
__________________________________________________________________
(___|a allele| __
|r allele| ____|S allele|__ _)
_________________________________________________
(___|a allele| __
__|R allele| ___ |S allele|__ _)
a. Is Tiffany an albino? ___yes
___ no
b. Does Tiffany have ___ sickle cell anemia or ___ normal blood?
c. Can Tiffany ___smell a particular odor or ____ can’t smell
odor?
7. Fill in the blanks of the following sentences.
A chromosome contains one long __________ molecule. Each gene in this
molecule gives the instructions for making a __________________.
Both chromosomes in a pair of ________________________ chromosomes have
the same ____________, but the two chromosomes may have different
_________________. Chromosomes that are not homologous have different
______________ which give the instructions for making different proteins.
8. Use the information on page 1 to explain why a person with aa alleles has very
pale skin and hair color. Include the words protein, enzyme and melanin in your
explanation
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Each human cell has 23 pairs of homologous chromosomes. Each of these
pairs of homologous chromosomes has its own unique set of genes. For example,
chromosome 11 has the genes shown in question 6. There are over 1000
additional genes on chromosome 11
Growth occurs when cells reproduce or make copies of them-selves. Mitosis is
the process by which a cell divides into two daughter cells, each of which has
identical chromosomes and same number of chromosome as the original cell.
Cells reproduce by dividing to make two cells. These two cells divide to make
four cells. Thus repeated cell division is responsible for growth. Recall the cell
theory-All cells come from pre-existing cells.
9. Even in a fully-grown adult, cells still undergo cell division. Why is this useful?
Think about your skin, for example.
II. MITOSIS ANIMATION-HOW EACH DAUGHTER CELL GETS A COMPLETE SET OF
CHROMOSOMES
VIEW THE ANIMATIONS BELOW AND DRAW AND LABEL THE STAGES OF THE
CELL CYCLE ON ATTACHED WORKSHEET. NEXT TO EACH DRAWING WRITE
WHAT IS OCCURING IN EACH STAGE.
http://www.sumanasinc.com/webcontent/animations/content/mitosis.html
https://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cyto
kinesis.html
http://vcell.ndsu.edu/animations/mitosis/movie-flash.htm
Questions:
This fill-in-the-blank question reviews the information from the animations and
worksheet and provides some additional explanations about the 6 steps that are
needed for mitosis to occur.
10. In preparation for mitosis, DNA is copied; this is called DNA
___________________.
11. DNA is wound tightly into compact chromosomes (each with two sister
_______________). These compact chromosomes are easier to move than the long
thin chromosomes in a cell, which is not undergoing cell division. Spindle
fibers, which will move the chromosomes, begin to form.
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12. Spindle fibers attach to the chromosomes and line the chromosomes up in
the middle of the cell.
13. Spindle fibers pull the sister ________________ apart to form separate
chromosomes which are moved toward opposite ends of the cell.
14. In a process called cytokinesis, the cell begins to pinch in half, with one set of
chromosomes in each half.
15. Two ______________ cells are formed. Each _______________ cell has received a
complete set of chromosomes. Each chromosome unwinds into a long thin
thread so that genes can become active and give the instructions for making
proteins.
16. For each of the figures below, give the number of the corresponding step
described above. Draw arrows to indicate the sequence of events during cell
division. (For simplicity, the figures show cells that have only 4 chromosomes (2
pairs of homologous chromosomes), but the basic process is the same as in human
cells, which have 46 chromosomes.)
separating
chromosomes
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17. Use an * to mark the arrow you drew which shows when sister chromatids
separate to form individual chromosomes.
Circle and label each pair of homologous chromosomes (HC)
18. Each of the daughter cells shown in step 16 can divide to produce two new cells.
What needs to happen before these cells will be ready for mitosis?
III. MODELING MITOSIS-HOW YOUR BODY MAKES NEW CELLS
a. Obtain a set of four pairs of pipe cleaners to represent chromosomes. One
color will represent chromosomes received from mom and the other color
will represent chromosomes received from dad. Recall chromosomes occur
in homologous pairs (homologous means having similar structure). One
member of a pair is received from dad and the other member of a pair is
received from mom (one color will represent chromosomes received from
mom and the other color will represent chromosomes received from dad).
b. Using masking tape label each chromosome with two letters one at the top
and one at the bottom. All letters placed on mom’s chromosomes should be
capital and all letters placed on dad’s chromosomes should be lower case. See
example below:
A
a
E.
e
B
b
F
f
C
c
G
g
D
d
H
h
c. Each different letter represents a different gene on a chromosome.
Lower case and uppercase letters represent alleles for the same gene.
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19. How many different genes are represented in you model? __________________
20. How many alleles are there for each gene is this model? ____________________
21. How many total alleles are in this model? __________________
d. Begin by assembling a diploid set of chromosomes, as they exist during
interphase prior to the S-phase and take a picture. A diploid set contains
pairs of homologous chromosomes. Each chromosome at this point will be a
single strand. Below is an example of a diploid set:
22. In the example above, what would be the diploid number of chromosomes? ______
23. How many homologous pairs of chromosomes are in the example above? ________
24. How many chromosomes came from mom? ___________
25. How many chromosomes came from dad? __________________
e. Move to the S-phase of interphase, where the amount of DNA doubles
because DNA replication occurs in S-phase.
26. Write a description of how DNA replicates
f. Since each chromosome doubled, select a matching pipe cleaner (same length
and same color) for each chromosome and slide both pipe cleaners through a
bead. You should now have a set of eight doubled chromosomes. Take a
picture.
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27. Draw a picture of a chromosome after S-phase of interphase and label sister
chromatids, centromere, & chromosome.
g. Review your worksheet from the animation and move the chromosomes
through the steps of mitosis-prophase/pro-metaphase, metaphase, anaphase,
telophase and then model cytokinesis. Take a picture of each step.
28. Describe your results by completing the following table.
Distribution of alleles During Mitosis
Which alleles were present in the original cell
(Before DNA replication)?
Aa,
Which alleles are present in each daughter cell
Produced by mitosis?
29. Are the alleles in the daughter cells produced by mitosis the same as or different
from the alleles in the original cell?
30. Explain how each daughter cell produced by mitosis receives exactly the same
alleles as the original cell had.
IV. Applying your knowledge
Fill in Table 1 with the correct information.
Table 1: Cell cycle and mitosis in fruit flies (fruit flies have four chromosomes)
STEP
NUMBER OF CELLS NUMBER OF
NUMBER OF
CHROMOSOMES IN HOMOLOGOUS
EACH NUCLEUS
PAIRS IN EACH
NUCLEUS
INTERPHASEBEFORE MITOSIS
CYTOKINESIS
AFTER MITOSIS
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31. What is the purpose of mitosis?
____________________________________________________________
A diploid set of human chromosomes contains 23 homologous pairs (46
chromosomes). Fill in Table 2 with the correct information regarding human body
cells.
Table 2: Cell cycle and mitosis in humans
STEP
NUMBER OF CELLS
NUMBER OF
CHROMOSOMES IN
EACH NUCLEUS
NUMBER OF
HOMOLOGOUS PAIRS
IN EACH NUCLEUS
INTERPHASEBEFORE MITOSIS
CYTOKINESIS AFTER
MITOSIS
32.Why is it necessary to double the amount of genetic material before mitosis
begins?
___________________________________________________________
___________________________________________________________
___________________________________________________________
33. The two daughter cells end up with an exact copy of the genetic material from
the parent cell. How does your simulation support this statement?
___________________________________________________________
___________________________________________________________
___________________________________________________________
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