Cell Cycle
Mitosis
Classwork
1. Parent Cell -> Daughter Cell -> Parent Cell. Describe the process involved in the transition between
daughter cell to parent cell.
2. Draw and label a chromosome. Include the following in your drawing. Sister chromatids, centromere,
chromosome, chromosome arm.
3. Describe the key events at each stage in the Cell Cycle. (G1, S, G2, M, C)
4. Draw and label the sub-phases of Mitosis and cytokinesis in an animal cell.
5. Discuss why interphase is the longest phase of the cell cycle.
6. Describe the additional steps necessary for a plant cell to complete cytokinesis.
7. The cell cycle has a number of checkpoints built in to the process of cellular division. Describe were some
of these check points can be found. Explain why they are necessary.
8. Describe the role of protein kinases and cyclin play in cell division.
9. Describe a substance that stimulates cell growth, division and differentiation. What kind of biological
molecule could they be?
10. A researcher is monitoring the kinase levels in a culture dish of frog connective tissue. She measures
a high concentration of MPF. Explain what MPF stands for; describe what the high levels indicate.
11. A biology student wanted to test the effect of the chemical hormone Kinetin on mitosis in plant tissue. Use
the data below and calculate the percent of cells that are mitotic and nonmitotic. Draw a conclusion from
the data.
Plant
Kinetin
Kinetin
No Hormone
No Hormone
Mitotic cells
Non-Mitotic
Mitotic
Non-Mitotic
Apple tree
52
80
28
102
Soybean plant
19
72
15
91
12. Scientist have found that normal cells culture in vitro will divide anywhere from 20 to 50 times. Describe
how this contrasts to cancer cells.
13. Explain the characteristics of both a benign tumor and a malignant tumor.
Homework
Alliums Root tip was observed by a biology student for mitotic division under a light microscope. All
observations we done at 200x.
Fill in the Data table below and answer the questions that follow.
Stages of mitosis
Total # of cells
# of cells in stage X 100%
Total # of Cell
Interphase
Prophase
Metaphase
Anaphase
Telophase
Totals
422
51
12
4
10
499
?
?
?
?
?
100%
14. From the data, which stage takes the longest? Explain why this stage took the longest.
15. A lab assistant streaks a petri dish of agar with a culture of E. coli bacteria on Friday afternoon. When he
returns on Monday morning the plate is full but not over flowing. Describe the control system that was
used by the E. coli to keep the colony size within the petri dish.
16. Some cells in the human body remain in G1, name two examples of this type of cell and provide a possible
explanation as to why they don’t divide.
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Cell Cycle
17. Describe what is necessary for a germ cell to by the G2 checkpoint and begin mitosis.
18. A cell proceeds into mitosis. After successfully completing prophase, it has failed the metaphase
checkpoint. Describe the action taken by the cell.
19. Chemicals known as cyclins and cyclin-dependent kinases regulate cell division. Both regulatory molecules
help move cell division in a systematically ordered fashion. Explain how the cell rids itself of cyclin and
cyclin-dependent kinases after having completed mitosis.
20. Breast cancer is a group of cancer cells found in the breast tissue. It is the second leading cause of death
in women. Briefly describe how it grows and metastases in the body.
21. Ortho Upstart™ is a plant chemicals used to stimulate root growth. It contains the Hormone Indole-butyric
acid. Use you knowledge of the cell cycle and describe what part the hormone affects.
22. Now that you know the effect of Indole-butyric acid, choose a variable and design an experiment to get
more specific results.
Read the following article: Cell shape changes during mitosis. Heidelberg, Universität (2013, February 12).
ScienceDaily and answer questions that follow.
http://www.sciencedaily.com/releases/2013/02/130212121800.htm
23. According to the author when does the mitotic spindle form?
24. Describe the chemical structure of actin, as well as the role of actin in the mitotic spindle.
25. Describe what the researchers were able to show from their experiment.
Meiosis
Classwork
26. Explain how the final product of mitosis and meiosis are different.
27. Compare and contrast haploid and diploid in cell division.
28. Explain the mechanisms that result in genetic variability in meiosis.
29. Describe what happens during each stage of meiosis.
30. Describe the term tetrad, and explain at which stage we would see it.
31. A chromosome has the alleles shown below at G1 in a cell that is about to enter meiosis. If crossing over
occurs at the arrow (^), sketch the new chromatids that will appear in the products of meiosis.
A
B
d
e
A
b
D
E
----+------+-----+------ +--+----+------+-----+-^
^
32. Trisomy 21, Trisomy 18, and Trisomy 13 are all examples of Aneuploidy. Describe the term aneuploidy
and explain how the above conditions are different from Turner syndrome.
Homework
33. Your body contains both somatic cells and sex cells. Describe the difference, and where they can be
found.
34. Meiosis is often referred to as “Reduction- Division” . Describe what is meant by this terminology.
35. Describe two events where the chance for genetic variability is increased during meiosis.
36. Calculate. If a cell has 22 chromosomes at G1, how many sister chromatids does it have during prophase I
of meiosis?
37. The cell is in entering prophase I (assume no crossing over takes place), what will the chromatids look like
at telophase II? (assume all X’s are homolous chromosomes in a single cell about to go through meiosis.
A A
x
A a
x
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b b
x
B B
x
D D
x
d d
X
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Cell Cycle
38. Meiosis can be divided into two stages, Meiosis I and Meiosis II. Which stage is most closely like Mitosis
and why?
39. Describe the term allele, and explain how it relates to the chromosome structure using the following
example. A brown heterozygous mouse which is homozygous dominant for pink eyes.
40. A Karyotype is a photograph of an organism’s chromosomes. Given the picture below describe the steps
that you would use to create a Karyotype.
1066 × 996 - contexo.info
Fertilization & Development
Classwork
41. Compare and contrast sexual and asexual reproduction.
42. Name 6 hormones involved in the process of sexual maturation in humans.
43. How does meiosis differ in men and women? Where does meiosis occur in each?
44. What does it mean that sperm is “stripped down”?
45. Compare and contrast internal and external fertilization. Give an example of a species that utilizes each
method.
46. Describe the acrosome and cortical reactions.
47. Differentiate be ectodermal, mesodermal, and endodermal layers.
48. Discuss the relationships between somatic cells, stem cells, and sex cells.
49. Describe why fruit flies (drosophila) are good candidates to use for genetic studies.
50. Draw a fruit fly and point out the following regions: Dorsal, ventral, anterior and posterior.
51. Describe relationship between the bicoid and RNA in the unfertilized insect egg. Also describe what
happens following fertilization.
52. The importance of the Hox – gene can be shown in the human condition known as polysyndactyly (the
development of extra digits). Describe the general role of the Hox- gene in developing cells.
Homework
53. Describe four examples of reproduction. Classify these as sexual or asexual reproduction.
54. Discuss the benefits of asexual reproduction and drawbacks of asexual reproduction.
55. GnRH, gonadotropins, estrogen, testosterone, LH, and FSH all play a role in puberty. Create a flow chart
illustrating the role of these hormones.
56. Define “polar bodies”. Where are they produced?
57. Explain why women over the age of forty have an increased risk of having a baby with Down Syndrome.
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Cell Cycle
58. “Mitochondrial Eve” is considered to be the first female that gave rise to all humans. Explain how cell
organelles are inherited in humans and why we propose a “Mitochondrial Eve” instead of a “Mitochondrial
Adam”.
59. Women have a 1/60 chance of having fraternal (two eggs, two sperm) twins and a 1/250 chance of having
identical (one egg, one sperm) twins. Explain why sesquizyotic twins (resulting from one egg and two
sperm) would be incredibly rare. Use appropriate terminology.
60. Discuss why scientists think stem cell therapy may be successful way to treat cardiovascular disease?
61. Describe the result if a researcher was able to place a higher concentration of bicoid at the posterior region
of a fly embryo.
62. Scientists have been able to insert Hox genes from mice into the fin of developing fish embryo and get
them produce legs. What significance could this research have regarding the evolution of legs in animals?
63. Sketch a developing embryo and shade in the picture showing the where RNA can be found. Also point
out the Head, thorax, abdomen, and tail.
64. In fruit flies, nurse cells surround the developing oocyte and synthesize proteins and RNAs that are to be
deposited in it. What would happen to the embryo if they were given a drug to kill the nurse cells?
Free Response
1. Antibiotics are chemicals that interfere with the cell cycle of
bacteria. Methicillin-resistant Staphylococcus aureus (MRSA) strains
were inoculated or grown in LB agar medium, and the listed
antibiotics were spotted identically on the surface of each of the
Vector plate. Dark halos at the position of each antibiotic spot show
the zone of growth inhibition produced by each antibiotic. The larger
the dark, circular halo is the greater the effect the antibiotic had on
the bacterial cell cycle or cell division.
Restoring Methicillin-Resistant Staphylococcus aureus Susceptibility to β-Lactam Antibiotics
Christopher M. Tan et. al.
Sci Transl Med 21 March 2012 4:126ra35
a. How does 1 bacterium, or a few bacteria, as grown in the agar plate shown above increase to be a
colony of billions of cells?
b. Why are bacteria, such as MRSA, able to become resistant to the effects of an antibiotic that is
frequently used?
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Cell Cycle
Origins of
Bilateral
Symmetry: Hox
and Dpp
Expression in a
Sea Anemone
John R.
Finnerty, Kevin
Pang, Pat
Burton, Dave
Paulson, and
Mark Q.
Martindale
Science 28 May
2004: 304
(5675), 1335-1337.
2. Developmental expression of Hox genes in
the sea
anemone Nematostella vectensis. The apical or aboral pole is toward the left and opposite to the blastoporal
pole (*, asterisks), the site of the future mouth. All images are seen from the lateral aspect (side view), except
for (B), which is an aboral view. Expression of anthox1 in (A) early blastula stage and (B and C) planula larva
stage. Expression of anthox1a in (D and E) gastrula and (F) late larval stages. Expression of anthox7 in (G and
H) gastrula and (I) late larval stages. Expression of anthox8 in (J and K) gastrula and (L) late larval stages.
Expression of anthox6 in (M) early larval stage and (N) juvenile polyp. bc, blastocoel; ec, ectoderm; ecph,
pharyngeal (ph) ectoderm; en, endoderm; enph, pharyngeal (ph) endoderm; enbw, body wall (bw) endoderm;
mes, mesentery; and tn, tentacles.
a. Provide a hypothesis for the following scenario: if you would express anthox1a in the early blastula
stage (A), what might you expect?
b. Create a diagram showing the progression of the Hox genes through the developmental stages of the
sea anemone.
c. How do the cell cycle and the expression of Hox genes help develop an organism such as the sea
anemone?
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Cell Cycle
Centrioles at the Checkpoint
Andrew W. Murray
Science 23 February 2001: 291 (5508), 1499-1502.
3. Centrosome behavior during the cell
division cycle. (A) Cells in G1 contain a
single centriole pair, composed of an old
(green bar) and a new (red bar)
centriole. Both centrioles are usually
located close to the nucleus (blue) and
are surrounded by components of the
centrosome (yellow dots), which initiate
microtubule assembly. The centrioles
duplicate conservatively during
interphase, producing two pairs each
composed of a mother centriole and a
daughter centriole (yellow bar). As cells prepare to enter mitosis, the two centrosomes (each containing a
centriole pair) move apart to opposite sides of the nucleus, so that they can act as the poles of the mitotic
spindle after the nucleus breaks down. In anaphase, the connection between the mother and daughter
centrioles is broken. (B) Centrosomal components and microtubules can organize themselves into a
centrosome-like structure in cells that lack centrioles. (C) Chromosomes (blue) can alter the local distribution of
microtubules; and chromosomes, microtubules, and microtubule motors can interact to form a bipolar spindle.
(D) Microtubules and microtubule motors (red dots) can self-organize in glass chambers the same size as
cells.
a. How are mitosis and interphase related in the cell division cycle?
b. Animal cells have centrioles, but some cells, like plant cells or bacteria, do not have centrioles, describe
some reason why centrioles might be important to animal cells?
c. The diagrams above depict mitosis and related processes. Some of the related processes are involved
during meiosis as well. Describe and draw how meiosis differs from mitosis.
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Cell Cycle
Requirement of Cks2 for the First Metaphase/Anaphase Transition of Mammalian Meiosis
Charles H. Spruck, Maria P. de Miguel, Adrian P. L. Smith, Aimee Ryan, Paula Stein, Richard M. Schultz, A. Jeannine Lincoln, Peter J. Donovan, and
Steven I. Reed
Science 25 April 2003: 300 (5619), 647-650.
4. To study the role of the CKS2 gene in the cell cycle, both alleles of the CKS2 gene were removed from wildtype, normal mice, generating CKS2–/– mice. Some of the results of the experiment are shown in figures A
and B. (A) Testis sections from adult wild-type mice were stained with hematoxylin and eosin (a dye that colors
nuclei blue-like and proteins pink-like). Spermatocytes (sperm cell precursors) in different stages of the cell
cycle can be seen (red arrowheads and green arrowheads. (B) Testis section from an adult CKS2–/– mouse
showing cells up to one stage or phase in the cell cycle (red arrowheads). Original magnification, ×400.
a. Describe the effect that the CKS2 gene product has on the cell cycle.
b. Why will CKS2–/– mice not be able to pass their genetic information to subsequent
generations?
c. How does the process shown in the cells in figure A affect the genetic diversity of the organism
that contains those cells and the offsprings that are produced by those cells?
5. Divergent silencing of duplicate genes in sister species.
The ancestral species may acquire a duplication of an essential
gene (represented by the black bars on two pairs of parental
nonhomologous chromosomes). Either copy of the duplicate gene
pair (white bars) may be randomly lost in the two descendant
populations through geographic isolation (living apart) or divergent
gene silencing (gene is turned off through mutations or
chromosomal modifications). In this case, the first-generation (F1)
hybrid progeny of these two populations will contain two “absentee”
alleles, one at each chromosomal locus. As a consequence of
independent assortment, 25% of the gametes produced by these
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Cell Cycle
individuals will be entirely lacking an active copy of the original ancestral, essential gene; therefore those
gametes would not be functional and produce nonfunctional progeny or be sterile. The above process repeated
over a period of time can produce new species from an ancestral population.
Gene Duplication and Evolution
Michael Lynch
Science 9 August 2002: 297 (5583), 945-947.
a. Once the duplicated gene is introduced into ancestral species, how is the gene maintained in
each cell of the species?
b. After the two isolated species are allow to mate and produce offspring (hybridization), why does
the hybrid contain one active and one silence allele of the essential, ancestral gene?
c. Describe or draw the allelic combinations that will be produced by meiosis in the hybrid
offspring?
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Cell Cycle
Cell Cycle-Answer Key
1. The parent cell will undergo mitotic division followed by cytokinesis. Following cytokinesis we now have a
daughter cell. When this cell begins mitosis it becomes the parent cell.
2.
3.
4.
5.
6.
G1 – cell growth. S – DNA replication. G2 – cell prepares for division. M – division of the nucleus.
Drawing similar to those found in the presentation.
Interphase is preparation for cell division. All cellular organelles must be replicated.
Because the plant cell has a rigid cell wall it will not pinch in during telophase. Instead a cell plate is
formed across the middle of the cell. The plate is formed from left over material from the mitotic spindle
and vesicles containing material to grow a new cell wall.
7. There are 3 major checkpoints at G1, S, and G2. They are necessary to check for errors before
proceeding to the next phase.
8. Kinases are enzymes that activate or inactivate proteins to drive or stop cell division. Cyclins are protein
enzymes that bind to kinases to make them active.
9. Growth factors are substances that stimulate cell growth, division and differentiation. They can act as
signaling molecules and can be protein or steroid hormones.
10. MPF is the maturation promotion factor. These high levels indicate the cells are ready to go into mitosis.
11. The hormone increases the amount of cells in mitotic division.
Plant
Kinetin
Kinetin
No Hormone
No Hormone
Mitotic cells
Non-Mitotic
Mitotic
Non-Mitotic
Apple tree
52/ 39%
80/61%
28/22%
102/78%
Soybean plant
19/ 21%
72/ 79%
15/14%
91/86%
12. Cancer cells divide uncontrollably. They do not respond to cell cycle checkpoints.
13. A benign tumor remains in a localized area and does not threaten the overall health of the organism. A
malignant tumor is detrimental to the organism. It grows uncontrollably and may spread to other areas of
the organism.
14. 84.6%, 10.2%, 2.4%, 0.8%, 2.0%. Interphase took the longest. This is the stage that the cell spends most
of its life preparing for cell division completing G1, S, and G2.
15. This would be density dependent inhibition. As the cells come into contact with other cells, a signal is sent
to keep growth in check.
16. Cardiac cell and nerve cell remain in G1. They are both very specialized cells and do not reproduce,
therefore never move out of G1.
17. At the G2 checkpoint the cell checks to make sure the chromosomes have been duplicated properly.
18. At this point the cell division will be halted and the cell will die.
19. The proteins are tagged by ubiquitin and get degraded by an enzyme called proteasome.
20. The tumor grows from a single cancer cell. Those cells invade neighboring cells. They spread through the
lymph and blood vessel to other parts of the body. Some may leave and take hold in another part of the
body.
21. There is an increase in cell division when using the hormone, which shows mitosis is positively affected.
22. Experiment should follow scientific method and provide measurable results.
23. The mitotic spindle forms just after the cell nucleus breaks down.
24. The mitotic spindle is made of actin filaments; this is the structural protein used to pull the chromosomes to
opposite poles during mitosis.
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Cell Cycle
25. They were able to show an actin regulator controls the structural changes necessary for the correct
distribution of genetic material after mitosis.
26. During mitosis, one diploid cell will divide into two identical diploid cells. During meiosis, one diploid cell will
divide into four different haploid cells.
27. The haploid number is half the number of chromosomes. The diploid number is the normal number of
chromosomes.
28. Independent assortment is the random distribution of maternal and paternal homologues. Crossing-over
during prophase I is when the genetic material between homologues exchanges places on non-sister
chromatids.
29. Prophase I – Nuclear envelope breaks down, spindle forms, homologous chromosomes form a tetrad,
crossing-over occurs. Metaphase I – Tetrads line up on the equator of the cell. Anaphase I – Tetrads split
moving chromosomes to the poles of the cell. Telophase I – Nuclear envelope reforms. Prophase II –
Nuclear envelop breaks down, spindle forms. Metaphase II – Chromosomes line up on the equator of the
cell. Anaphase II – Sister chromatids separate and move to the poles of the cell. Telophase II – Nuclear
envelop reforms.
30. A tetrad is when two homologous chromosomes line up together during prophase I and metaphase I. Four
copies of each gene exist in a tetrad.
31. ----A------B----d ------E
A------b-----D-----e
32. Aneuploidy is a result from an abnormal meiotic division. The first 3 conditions are caused by abnormal
separation of chromosomes during meiosis I at those specific chromosomes. Turner syndrome is a partial
or complete absence of the second sex chromosome.
33. Somatic cells contain the diploid number of chromosomes and can be found in all body cells except sex
cells. Sex cells are sperm or egg cells that contain the haploid number of chromosomes.
34. The number of chromosomes is halved through the process of meiosis I and then in meiosis II each new
daughter cell is divided again.
35. During prophase I, crossing-over occurs, and genetic information trades places on homologous
chromosomes. During metaphase I, chromosomes line up independently along the equator.
36. 44 chromatids
37. AbD; AbD; aBd; aBd
38. Meiosis I is most closely like mitosis. Homologous chromosomes are separated into two daughter cells.
39. An allele is an alternative form of a gene. An organism gets one allele from each parent. A mouse that is
heterozygous has one dominant allele on the chromosome from one parent and one recessive allele on the
chromosome from the other parent. For the homozygous, they have the same version of the gene on each
chromosome.
40. The homologous chromosomes would be matched and placed side by side. Each pair would be arranged
from biggest to smallest. Chromosomes are measured according to arm length and overall size.
41. Both involve the production of a new organism. Asexual involves one parent and is accomplished by
fission, budding, or regeneration. Sexual reproduction divides by meiosis. Asexual reproduction requires
less energy but results in identical offspring. Sexual reproduction requires one to expend energy in the
process of mating, but results in greater genetic variation in the population.
42. Estrogen, testosterone, follicle-stimulating hormone, gonadotropins, luteinizing hormone, gonadotropinreleasing hormone.
43. Meiosis occurs in the testes of men at puberty. Meiosis I and meiosis II are completed sequentially
throughout the adult life of the man, producing 4 sperm for every germ cell. Meiosis occurs in the ovaries
of women. Meiosis I occurs in women before they are born, and is then arrested until the onset of puberty.
At puberty, women produce 1 to 2 eggs approximately every 28 days by completing meiosis II. Meiosis in
women results in 1 egg and 3 polar bodies for every germ cell.
44. Sperm only contain the necessities for life – a nucleus, mitochondria, a protein coat, and enzymes for
breaking through the barriers on the surface on an egg.
45. External fertilization is the joining of egg and sperm outside the body, as in fish or amphibians. Internal
fertilization is the joining of egg and sperm inside the body, as in mammals and birds.
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46. The acrosome reaction occurs when sperm release enzymes to break through the barriers on the surface
of the egg cell. Once the sperm has reached the plasma membrane of the egg, it fuses to it and releases
its DNA into the cell. The cortical reaction occurs in response to sperm DNA entering the egg cell. The
egg undergoes a series of chemical and electrical reactions which fuse the membrane and prevent other
sperm from entering.
47. Ectodermal cells are the outer most layer of the embryo and give rise to the brain, nervous system, outer
layer of skin, outer layer of organs, and sensory organs. Mesodermal cells are the middle layer of the
embryo and give rise to most internal organs, the inner layers of skin, and muscles. The endodermal layer
is the innermost layer and gives rise to the respiratory and digestive systems.
48. Somatic cells are body cells (such as neurons, muscle cells, and cardiac cells); these cells are diploid.
Stem cells are undifferentiated cells; they have the potential to become a specialized cell such as a
leukocyte or a cardiac cell (they are diploid). Sex cells are haploid cells (eggs and sperm) which must fuse
together to generate the first embryonic stem cell.
49. Fruit flies are small organisms; they require very little room to carry out their life cycle. They reproduce
quickly and have only 8 chromosomes to study.
50. Anterior (head), posterior (tail), dorsal (back), ventral (belly)
51. The bicoid genes cause the production of RNA in the cytoplasm. This production will establish a gradient
across the cell’s cytoplasm due to the location of the nucleus. After fertilization, newly dividing cells will
contain differing amounts of bicoid RNA, which help establish the head the tail region of the insect.
52. Hox genes are homeotic genes that influence the expression of transcription factors along the axis of the
body.
53. Fission (asexual) is one cell copying its DNA and dividing into two cells. Budding (asexual) is when a few
cells from a parent organism “bud off” and grow into an adult organism. Fragmentation (asexual) is when
an offspring grows from a part of the parent organism that has been broken off. Sexual reproduction is
when two organisms produce haploid sex cells which combine to generate a new offspring.
54. The benefits of asexual reproduction are decreased expenditure of energy, increase rate of reproduction,
and genetic fidelity to the parent. The drawback is decrease genetic variation in the population.
55. GnRH  Gonadotropins  LH  Estrogen in women
Testosterone in men
 FSH production of sperm in men
Estrogen in women
56. Polar bodies are non-functioning egg cells, resulting from unequal division during meiosis in the ovaries of
females.
57. Women complete meiosis generating an egg cell once every 28 days. As they age, cells have been
arrested in meiosis for longer periods of time. This increases the likelihood of nondisjunction occurring
during the completion of meiosis.
58. Organelles in human cells are inherited solely from the mother, as the sperm is a stripped down version of
a cell. Mitochondrial Eve is proposed rather than “Adam” because when sperm fuse with eggs they inject
only their nucleus into the cell.
59. Once a sperm has fused to the egg membrane and inserted its DNA, the cortical reaction occurs
preventing other sperm from entering the egg.
60. Stem cells are undifferentiated cells that may be used to regenerate cardiovascular vessels rather than
transplant vessel from other areas of the body.
61. The fly would produce a head at the wrong end (or a head at each end).
62. This may show that a mutation occurred in a fish which allowed for land-dwelling organisms.
63. Sketch should resemble the presentation
64. The RNA would not be distributed in a way that indicates a gradient. This would make it difficult to
establish a head and tail region.
1. Antibiotics
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Cell Cycle
a. Bacteria increase in number by binary fission. Binary entails growing to a sufficient size,
duplicating the bacterial chromosome, and dividing into two cells. Binary fission repeated over
many generations yields a population of bacteria only limited by the nutrients in the
environment.
b. By chance a small subset of bacteria within a population of cells will be resistant to the
antibiotic. The subset will survive the initial administration of the antibiotic and reproduce well in
an environment with more nutrients and less competition from other bacteria. Subsequent
administration of the antibiotic will repeat the selection process from subsets in new population
that are even more resistant to the antibiotic. In due time, the antibiotic would be obsolete,
because it will not be able to stop the bacteria from entering the cell cycle.
Learning Objectives:
LO 3.9 The student is able to construct an explanation, using visual representations or narratives, as to how
DNA in chromosomes is transmitted to the next generation via mitosis, or meiosis followed by fertilization. [See
SP 6.2]
LO 1.4 The student is able to evaluate data-based evidence that describes evolutionary changes in the genetic
makeup of a population over time. [See SP 5.3]
LO 1.5 The student is able to connect evolutionary changes in a population over time to a change in the
environment. [See SP 7.1]
2. HOX genes
a. A number of events might happen. A blastopore might not form since an axis is not determine
by anthox1, the growth in length of the blastula/gastrula might be perpendicular to the
blastopore, or the inner digestive cavity of the sea anemone might not form properly.
b. Developmental Stages
BLASTULA
anthox
GRASTULA
anthox1a
anthox7
anthox8
LARVAL
POLYP
anthox6
c. The expression of the Hox genes in
a certain
location and time during the development of the sea anemone directs the cell cycle and
regulates the expression of other genes needed to differentiate the cells into functional tissues
and/or organs to make a viable organism. The initial Hox gene (anthox) might signal a cascade
of other genes to be produced and start the expression of other Hox genes, such as anthox1a,
and those Hox genes may progressively activate the expression of the other Hox genes until
development is complete.
Learning Objectives:
LO 2.31 The student can connect concepts in and across domains to show that timing and coordination of
specific events are necessary for normal development in an organism and that these events are regulated by
multiple mechanisms. [See SP 7.2]
LO 2.32 The student is able to use a graph or diagram to analyze situations or solve problems (quantitatively
or qualitatively) that involve timing and coordination of events necessary for normal development in an
organism. [See SP 1.4]
LO 2.33 The student is able to justify scientific claims with scientific evidence to show that timing and
coordination of several events are necessary for normal development in an organism and that these events are
regulated by multiple mechanisms. [See SP 6.1]
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Cell Cycle
3. Mitosis/Meiosis
a. Before a cell divides, certain steps have to be carried out to make sure both cells get what they
need. These steps are carried out in interphase. The cell needs to produce the proteins that will
carry out the synthesis of DNA, organelles need to be reproduced (chloroplast , mitochondria,
centrioles), DNA needs to be copied, and more proteins and organelle size must increase along
with cell size. Then, mitosis or cell division could occur.
b. Animal cells tend to be more complex than the cells without centrioles; the mechanisms that
handle the DNA of the animal cell must be able to be reproduced without flaws many times
over. The centrioles would provide a level of fidelity and stability that can be reproduced from
cell division to cell division. The centrioles might assist animal cells to assume many shapes
and help produce cytoskeletons that protect the nucleus and its contents.
c. Meiosis produces cell with a different genetic makeup than the parent cells. Mitosis produces
cell with the identical genetic makeup of the parent cell. Meiosis involves 2 cell divisions instead
of 1 for mitosis. The DNA is not copied again in the second cell division, so the daughters get
half the amount DNA as the parent cell. The chromosomes line up differently on the metaphase
axis. Homologous chromosomes line up next to each other in the same orientation of mitotic
spindle; the chromosomes are divided into 2 cells with half the number of chromosomes as the
parent. The subsequent cell division is comparable to mitosis. All the chromosomes line up in
the middle of the cell, and each chromosome copy is divided into 2 cells, yielding a total of 4
haploid cells.
Learning Objectives:
LO 3.7 The student can make predictions about natural phenomena occurring during the cell cycle. [See SP
6.4]
LO 3.8 The student can describe the events that occur in the cell cycle. [See SP 1.2]
LO 3.9 The student is able to construct an explanation, using visual representations or narratives, as to how
DNA in chromosomes is transmitted to the next generation via mitosis, or meiosis followed by fertilization. [See
SP 6.2]
4. Mutation
a. The CKS2 gene stops the precursor of sperm cells from completing meiosis, and the CKS2–/–
mice are sterile and produce no viable sperm cells. The cells arrest or stop at metaphase I of
meiosis.
b. CKS2–/– mice cannot complete meiosis and no mature sperm can be generated. Sexually
reproducing organisms must be able to complete meiosis and produce mature sperm to pass
their genetic material, at least 50%, to the next generation.
c. Meiosis reduces the chromosome number in half to be restored during fertilization, generating a
combination of genetic traits from both parents. Meiosis creates new combinations between the
homologous chromosomes during crossing over in prometaphase I of meiosis, increasing
genetic diversity. Homologous chromosomes line up independently, at random in the middle of
the cell; so many different combinations of traits can be produced.
Learning Objectives:
LO 2.31 The student can connect concepts in and across domains to show that timing and coordination of
specific events are necessary for normal development in an organism and that these events are regulated by
multiple mechanisms. [See SP 7.2]
LO 3.11 The student is able to evaluate evidence provided by data sets to support the claim that heritable
information is passed from one generation to another generation through mitosis, or meiosis followed by
fertilization. [See SP 5.3]
LO 3.10 The student is able to represent the connection between meiosis and increased genetic diversity
necessary for evolution. [See SP 7.1]
www.njctl.org
PSI AP Biology
Cell Cycle
5. Duplicate Genes
a. The duplicated gene is maintained by the cell cycle, specifically the S phase of interphase. In S
phase the DNA is semi-conservatively copied to generated sister chromatids of each
chromosome.
b. Each species can produce only one type of sperm cell: one silenced long and one active short
chromosomes or one active long and one silenced short. Those two gametes or sex cells will
produce an diploid organism with one silenced and one active long chromosome and one
silenced and one active short chromosome (the hybrid organism).
c. Non-functional allelic combination, both alleles silenced.
www.njctl.org
PSI AP Biology
Cell Cycle