Download APEX Unit 4 Answers

4.1.1 Read: Cell Reproduction
AP Biology Sem 1 (S3043799)
Reading Guide
Name: ____________________
Date: ____________
Reading Assignment: Principles of Life (2nd edition)
Please read the following sections of your textbook. As you read, use this reading guide to check your
understanding of the material.
Part
Reading Assignment
I
Chapter 7
The Cell Cycle and Cell Division (7.1, 7.2, 7.3, 7.4, 7.5)
II
Chapter 3
Nucleic Acids, Proteins, and Enzymes (3.1)
Chapter 8 Inheritance, Genes, and Chromosomes (8.3, 8.4)
Chapter 9 DNA and Its Role in Heredity (9.1, 9.2)
Part I
Describe the products of asexual reproduction.
The new organisms are identical copies of the parent. Genetic variation in organisms produced by
asexual reproduction can only be due to mutations.
Compare haploid and diploid cells.
Haploid cells are cells that contain half as much (n) genetic information as a diploid cell (2n). In humans,
haploid cells are gametic cells (sperm and eggs), and diploid cells are somatic cells (body cells).
Identify and describe the three steps of the cell cycle.
Interphase: This is the growth phase and includes DNA replication. The cell nucleus is visible.
Mitosis: This is when nuclear segregation of DNA takes place.
Cytokinesis: This consists of cell division and formation of a cleavage furrow in animals and a cell plate in
plants.
In the space below, draw a chromosome with sister chromatids, a centromere, and kinetochores.
Students should draw an image of a chromosome as on page 129.
Describe the function of the spindle.
The spindle serves as the structure to separate the sister chromatids during mitosis.
In the space below, identify the phases of mitosis and draw a typical cell in each of the phases. Then
describe the events that occur during each of the phases.
Phase
(Students' drawings should resemble those on
pp. 130 - 131.)
Events
Prophase
During prophase, the condensed chromosomes,
the centrosome, and the spindle are present.
Prometaphase
The nuclear envelope disintegrates and the
chromosomes (which are very condensed at this
point) attach to the kinetochore microtubules.
Metaphase
The chromosomes are lined up on the equator
(metaphase plate) to prepare for segregation.
Telophase
Separation of the chromatids occurs as each
sister chromatid moves toward each end (pole) of
the cell.
Explain the structural differences between cytokinesis in animal cells and in plant cells.
A cleavage furrow (pinching of the cell membrane) occurs during cytokinesis in animals. The membrane
is able to pinch in because it is composed of contractile proteins. The microfilaments that are composed
of these proteins form a ring on the surface of the membrane. In plant cells, vesicles from the Golgi
apparatus fuse together, form a new plasma membrane, and distribute their contents to form a new cell
plate.
How do cells know when to enter the cell cycle to divide?
Eukaryotes do not divide whenever environmental conditions are appropriate the way prokaryotes do.
They require growth factors to stimulate cell division and differentiation. Eukaryotic cells divide to repair
damaged cells, replace dead cells, or for growth purposes.
In the space below, draw a picture of the eukaryotic cell cycle and label the subphases and checkpoint.
Students should draw an image as on page 133.
Describe the function of a cyclin-dependent kinase.
Cdks become active by binding to a cyclin protein. This interaction causes the Cdk to change shape so
that its active site is open. Each Cdk has a particular shape and therefore a particular cyclin protein that
can activate it. If a growth factor is released, cyclin proteins will be synthesized. These will interact and
activate the corresponding Cdk, which will cause the cell cycle to proceed.
Describe how the function of meiosis differs from that of mitosis.
Meiosis functions as a reductive division process (from diploid to haploid). The purpose is to create
daughter cells that contain half as much genetic information (as compared to a full complement in mitosis)
yet contain a complete set of chromosomes for reproductive purposes. During the process, variation is
generated (whereas no variation is generated in mitosis).
In the space below, draw mitosis as compared to meiosis. Use different colors for different chromosomes
and label each cell as haploid or diploid.
Students should draw images as seen on page 135.
Explain the mechanism of crossing over during prophase of meiosis I, and describe how it generates
genetic variation.
During crossing over, homologous chromosomes pair up in synapsis (in what is called a tetrad). In
synapsis, genetic material is exchanged between nonsister chromatids of the homologous chromosomes
at locations called chiasmata. This ensures that the chromosomes are reshuffled and contain varying
alleles of the same genes (genetic variation).
In the space below, draw a recombinant chromosome.
Students should draw an image similar to that on page 139.
What happens when something goes wrong in meiosis? In the space below, list the possible errors during
meiosis, describe the events, and explain their consequences for offspring.
Meiotic error
Nondisjunction
Description
Explanation of consequences
The failure of a homologous
chromosome to separate at
anaphase I or the failure of sister
chromatids to separate at
anaphase II
Anaphase I consequence: Two of
the four daughter cells will have
both copies of the homologous
chromosome, and two daughter
cells will have none.
Anaphase II consequence: Two
daughter cells will be normal.
One daughter cell will have one
extra chromosome, and one
daughter cell will be missing one
chromosome.
Polyploidy
Extra sets of chromosomes are
Speciation (often in plants)
present (3n, 4n, ..., xn). This can
be caused by extra DNA
replication, no spindle formation
in meiosis II, and all
chromosomes going to one cell,
with none separating to the other.
Translocation
Chromatids break and rejoin
during prophase (crossing over)
of prophase I.
Can be deleterious to offspring
Explain the purpose of apoptosis.

Removal of cells that are no longer needed (development)

Removal of cells that are damaged due to old age
In the space below, draw a flow chart describing the events of apoptosis.
Students should draw an image as on page 141 with the labels 1a, 1b, 2, and 3.
Part II
Describe the structure and function of a bacteriophage.
Bacteriophages are viruses that infect bacteria. They have DNA and perhaps a few different types of
proteins. However, upon infection of a bacterial cell, the virus uses the bacterial cell's machinery to
replicate its viral genetic information.
Describe Chargaff’s rule.
The total number of purines (adenine and guanine molecules) will equal the number of pyrimidines
(thymine and cytosine molecules) if the DNA molecule is a double helix. Therefore, if we know the
abundance of one or two bases in a DNA molecule, we can deduce the complete composition of the DNA
molecule.
As an example, if we know that 20% of a given DNA molecule is composed of adenine, what are the
other percentages?
The entire molecule is equal to 100%. Use the formula below to calculate the rest of the percentages.
A+G=T+C
A = 20, therefore T = 20. A + G = T + C, and A + T + C + G = 100. Therefore C + G = 60. C = 30, G = 30.
An important discovery in the study of DNA was that DNA is replicated semiconservatively. In the space
below, draw a semiconservative round of replication using two different colors for the parental strands
and the new strands.
Students should draw an image similar to the image on page 172.
To which end are nucleotides added to the growing new strand during DNA replication? Why?
The nucleotides are always added to the 3' end (forming a new 5' → 3' strand). This is due to the
necessary orientation for the formation of the bond.
How does the quantity of origins of replications differ in number in prokaryotes and eukaryotes? What
would be the consequences to eukaryotes if they used the same number of origins?
The number of origins is higher in eukaryotes, as their DNA is linear and larger (up to a billion bp).
Without multiple origins, the time necessary for replication in eukaryotes would be very long.
For each of the following structures or enzymes necessary for DNA replication to occur, describe the
function.
Structure/Enzyme
Function
Primer
Starter strand made up of RNA; degraded after
DNA replication occurs; necessary for DNA
replication to begin
Primase
Enzyme that synthesizes the RNA primer
DNA polymerase
Enzyme that catalyzes the polymerization of the
DNA nucleotides on the leading and lagging
strands
Leading strand
Continuous replication at the 3' end
Lagging strand
Discontinuous replication away from the replication
fork
Okazaki fragment
Section of DNA nucleotides assembled in a
discontinuous pattern on the lagging strand
DNA ligase
Enzyme that catalyzes the formation of a
phosphodiester linkage between adjacent Okazaki
fragments on the lagging strand
Telomere
Repetitive sequences at the end of a chromosome
(for instance, TTAGGG x 2500). They function to
protect the chromosome.
Telomerase
Enzyme that catalyzes the formation of any lost
telomeres
In the space below, draw a typical DNA replication fork and label the structures and enzymes listed
above.
Students should draw an image similar to that on page 175.
Explain antiparallelism as it relates to DNA formation.
DNA must be synthesized in the 5' to 3' direction. Since only the 3' ends can support continuous
replication, one strand gets built in one direction, and the other strand gets build in the opposite direction.
The analogy of a cross highway where cars are traveling in different directions next to one another
applies to how the DNA molecule is replicated.
Key Terms
As you come across these terms during your reading, write your own definition in the space provided.
Asexual reproduction
The production of offspring that are genetically identical to the single parent (and other offspring produced
by that parent). It may be accomplished by binary fission of prokaryotes, by mitotic cell division of
unicellular eukaryotes, by fragmentation or various forms of budding, or by development of an unfertilized
egg (parthenogenesis).
Clone
A genetically identical cell or organism.
Mitosis
The process of nuclear division in which two identical daughter nuclei are produced by an original
parental nucleus. Mitosis is typically, but not necessarily, accompanied by cell division.
Meiosis
The double division of a nucleus to produce four haploid nuclei from an original diploid parental nucleus
that has undergone chromosome replication. Meiosis is accompanied by cell division.
Chromosome
A structure that contains a single DNA molecule and associated proteins and that is found in the nucleus
of eukaryotes and in the cells of bacteria and archaea. In eukaryotes there are typically several or many
linear chromosomes. In bacteria and archaea there is one circular chromosome.
Chromatin
The material from which eukaryotic chromosomes are composed. It contains DNA and proteins.
Somatic cells
Cells of the body of a multicellular organism, excluding the gametes and the cells that give rise to them.
Homologous pairs
A pair of chromosomes containing genes that code for the same proteins.
Haploid
Describes a cell or organism with one copy of each chromosome.
Diploid
Describes a cell or organism with two copies of each chromosome.
Zygote
The cell that results from fertilization.
Fertilization
The union of gametes.
Binary fission
Separation into two similar and genetically identical individuals, especially by division of the cell in
prokaryotes, but also by division of the multicellular body in some eukaryotes.
Segregation
The separation of sister chromatids during mitosis or meiosis; results in one copy of each chromosome
being passed on to offspring during fertilization.
Cell cycle
The sequence of events that occur between one nuclear division and cell division and the next in a
eukaryotic cell.
Interphase
The phase of the cell cycle between cell divisions.
Prophase
The first phase of a nuclear division in mitosis and meiosis, during which the chromatin becomes
condensed and the spindle begins to form.
Sister chromatids
copies of a single chromosome that are produced during DNA replication
Centromere
A chromosome region at which sister chromatids attach and to which spindle fibers attach.
Kinetochores
Structures that form on the centromeres of eukaryotic chromosomes. Spindle fibers attach to them during
mitosis or meiosis.
Karyotype
The shape, size, and number of the chromosomes of a eukaryotic organism.
Centrosome
A structure in animal cells that contains the centrioles and that acts as a microtubule-organizing center for
the spindle during mitosis or meiosis.
Centriole
A self-replicating organelle of eukaryotic cells (excluding plants, most fungi, and some protists) that
organizes the microtubules that form the spindle during mitosis and meiosis.
Spindle apparatus
The structure of microtubules that forms in cells undergoing mitosis and meiosis and that functions to
move chromosomes to opposite poles of the cell.
Daughter cell
A cell produced by cell division.
Growth factors
proteins capable of stimulating growth, proliferation and differentiation of cells.
Cyclin dependent kinases (Cdks)
An enzyme that acts to stimulate some aspect of the cell cycle when it is bound by a cyclin.
Checkpoint
A point during the cell cycle when the status of the cell is assessed and the cell cycle either proceeds to
the next stage or remains at the present stage.
Condensation
A change in state from a more diffuse form to a more dense form, such as occurs to chromatin during
mitosis or meiosis, when it changes from a diffuse form to compact chromosomes.
Crossing over
The process by which segments of genes of homologous chromosomes are exchanged during meiosis
Tetrad equatorial (metaphase) plate
The location where crossing over takes place during meiosis
Recombinant
Describes a molecule of DNA composed of segments originating from two sources, such as two
homologous chromosomes or two species.
Independent assortment
The independent segregation (with a gamete's two alleles for two genes coming from the same
chromosome or coming from different chromosomes by random chance) of the alleles of two or more
genes into different gametes.
Nondisjunction
Nondisjunction occurs when homologous chromosomes or sister chromatids fail to separate properly in
meiosis, and both chromosomes or chromatids segregate to one daughter nucleus. This produces one
daughter nucleus with two copies and one daughter nucleus with no copies of the chromosome.
Polyploidy
A condition in which an organism or cell has more than two complete sets of chromosomes.
Aneuploid
An organism or cell that has an abnormal number of chromosomes as a result of extra or missing
individual chromosomes (rather than whole sets).
Translocation
A type of mutation in which a portion of a chromosome is detached and joined to another chromosome.
Apoptosis
A programmed cell death.
Caspases
A group of proteins that are involved in initiating and carrying out apoptosis.
Oncogene
A gene that when mutated causes cancer.
Tumor suppressor gene
A gene for a protein that is involved in a signal pathway that prevents mitosis.
Bacteriophage
Viruses that infect bacteria.
Transformation
The alteration of a genotype and phenotype through the uptake of environmental DNA.
Purine
A double-ring nitrogenous base.
Pyrimidine
A single-ring nitrogenous base.
Semiconservative replication
The model of DNA replication, in which each daughter DNA double strand consists of one complete
parent strand paired with a complete daughter strand. This is different from the models of conservative
replication and dispersive replication, which do not occur in cells.
Template strand
The single strand of DNA from which a new DNA strand is being synthesized.
Deoxyribonucleoside triphosphate (dNTPs)
The form of a nucleoside that is incorporated into a new DNA strand using the energy of the phosphate
bonds to form phosphodiester bonds between nucleotides.
DNA polymerase
In DNA replication, an enzyme that adds single nucleotides to the growing DNA strand.
Origin of replication
The point at which DNA replication begins on a chromosome.
Replication fork
The structure formed during DNA replication when the double helix is unwound, forming two single-strand
regions.
Primer
A short sequence of RNA nucleotides that is added to the exposed 3' end of a single DNA strand at the
beginning of replication. DNA polymerase is then able to add new nucleoside triphosphate molecules to
the primer.
Primase
The enzyme that adds a primer to initiate DNA replication.
Topoisomerase
An enzyme that affects the shape (topology) of the DNA molecule; it unwinds the DNA molecule by
causing single-strand nicks in the backbone.
Leading strand
The strand of DNA on which a new DNA strand is synthesized continuously, toward the replication fork.
Lagging strand
The strand of DNA on which a new DNA strand is synthesized discontinuously, away from the replication
fork.
Okazaki fragment
Okazaki fragments are synthesized in a discontinuous fashion on the "lagging strand" because the
replication fork is moving in the 5' to 3' direction, while the lagging strand is being synthesized in the
opposite direction.
DNA ligase
The enzyme that links the backbone of the strand of replicated DNA together.
Telomere
A region at the ends of eukaryotic chromosomes composed of many repeated short sequences that
prevents the shortening of the chromosome during replication.
Telomerase
An enzyme that replenishes lost telomere segments after DNA replication.
4.1.3 Study: Modeling DNA Replication
AP Biology Sem 1 (S3043799)
Study Sheet
Name: ____________________
Date: ____________
1. Several enzymes participate in DNA replication. In the column on the left, write the correct
enzyme type next to each description. Enzyme types: DNA polymerase, helicase, ligase,
topoisomerase
Replication Enzymes
Type of enzyme
Description
Helicase
Opens DNA double helix
Topoisomerase
Clips and unwinds DNA
DNA polymerase
Adds nucleotides and corrects errors
Ligase
Seals DNA strands together along its length
2. In what way is inference related to direct observation?
Inference is the process of formulating a conclusion based on indirect evidence rather than on direct observation.
3. In what way does the coiling of DNA as a helix affect the position of its 3' and 5' ends?
The 3' and 5' ends remain in the same locations on the DNA molecule. The 3' end of one strand is linked to the 5'
end of the other strand, and vice versa.
4. What is semiconservative replication in DNA?
Semiconservative replication means that each replicated DNA molecule consists of one strand of original DNA and
one strand of newly synthesized DNA.
5. In the area below, draw a simple representation of a DNA replication fork with Okazaki
fragments. Label the Okazaki fragments, the leading and lagging strands, and the 5' and 3' ends.
Use arrows to show the direction of replication.
4.1.5 Study: Cell Cycle Checkpoints and Cancer
AP Biology Sem 1 (S3043799)
Study Sheet
Name: ____________________
Date: ____________
As you read through the study, use this study sheet to help you organize your thoughts and collect data.
Record the events that occur during each phase or checkpoint of the cell cycle.
Phase or checkpoint
Events/Requirements
G1 phase
Cell growth
Duplication of cell structures
G1 checkpoint
Cell-size check
Growth factors present
DNA error check
S phase
Chromosome replication
Duplication of cell structures
G2 phase
Cell growth
G2 checkpoint
Cell-size check
Chromosome replication check
DNA error check
DNA error correction
First portion of M phase
Spindle fibers attach to chromosomes
M-spindle checkpoint
Spindle-fiber attachment check
Second portion of M phase through cytokinesis
Chromosome separation
Cytoplasm division
Daughter-cell formation
In the area below, identify the error for each of the following cells.
Cell β
Insufficient organelles are present.
Cell θ
Mutations are present.
Cell Ψ
The cell is not large enough to proceed.
Cell
A chromosome did not attach to the spindle apparatus.
For each of the following processes, explain how nondisjunction can cause varying consequences to the
individual and offspring.
Process
Consequence
Mitosis
When nondisjunction occurs during mitosis, the
effects are only on the immediate daughter cells,
not on the gametes and therefore not on the
offspring.
Meiosis
When nondisjunction occurs during meiosis, the
gametes are affected, and therefore the offspring
are affected
4.1.7 Practice: Cell Reproduction
AP Biology Sem 1 (S3043799)
Points possible: 25
Practice Assignment
Name: ____________________
Date: ____________
1. During human embryonic development, many neurons arise and form connections with one another.
However, much later these same neurons are found to be absent. Describe the process that accounts for
this loss of early neurons, and explain how this process achieves the changes described. (5 points)
Answer: Some neurons that arise early in development later die during apoptosis, which is a normal,
programmed process of cell death. Cells may arise during an early stage in development because they
are necessary to create an environment for later stages of development. These early cells may not retain
their usefulness once the organism has reached a certain stage of development. Apoptosis ensures that
these cells are removed at the right time, so they do not take up valuable energy reserves or interfere
with the continuing maturation of the organism.
2. The transmission of genetic information from parent to daughter cells is highly accurate. Describe the
features of DNA replication responsible for this fidelity of information transfer. Explain why this
mechanism allows the high level of accuracy of information transfer that is observed. (5 points)
Answer: Genetic information is encoded in a sequence of bases along a strand of DNA. This strand of
DNA is copied during cell division to form two daughter cells from a parent cell. The high accuracy of
copying the parent DNA comes about because the parent strand can be used as a template for building a
daughter strand. DNA synthesis involves specific pairing of new bases in the daughter strand to existing
bases in the parent strand. This base pairing ensures that the same sequence of bases is transmitted at
each replication phase, which ensures that the genetic information transfer remains highly accurate no
matter how many generations go by.
3. DNA is the primary source of heritable information in cells. Explain how the chemical structure of DNA
makes this possible. (5 points)
Answer: DNA is a polymeric molecule composed of a sugar phosphate backbone bonded to four different
nitrogenous bases. Although the sugar phosphate backbone is chemically the same throughout the
polymer, the sequence of the four bases bonded to this backbone varies. Genetic information is encoded
in the linear sequence of bases in the DNA molecule.
4. Compare and contrast the processes of sexual reproduction in eukaryotes and conjugation in bacteria
in terms of how they contribute to genetic variation in a population. (5 points)
Answer: In bacterial conjugation, genetic material moves directly from one organism to another. This is a
one-way type of sharing of genes that allows the recipient to obtain new alleles. Thus, each generation of
bacteria can itself undergo genetic transformation as alleles become mixed through conjugation.
In sexual reproduction, genetic material does not move between individuals, but rather two individuals
donate genetic material that is then combined in the formation of new offspring. Thus, genetic variation
occurs as mating produces new mixes of alleles in the new generation. However, sexual reproduction
does not allow genetic changes to the parental generation, as it does in bacterial conjugation.
5. A population of the species Polymita picta is shown in the image below. Explain two mechanisms that
could have contributed to the variations apparent in this population.(5 points)
Answer: Variation in a population is due to differences in alleles present in the gene pool for that
population. These variations arise as the result of random assortment during meiosis and also during
mutation events, some of which occur at low frequency as errors during DNA replication or RNA
transcription
4.1.9 Discuss: Meiosis and Mitosis
AP Biology Sem 1 (S3043799)
Points possible: 15
Discussion
Name: ____________________
Date: ____________
This worksheet will help you organize your thoughts for the discussion. Answer the questions and
prompts below to help you prepare for the discussion.
1. Predict the consequences to sexual reproduction if meiosis did not occur and all cells divided
mitotically. Discuss chromosome number, variation, and the implications of these changes on the success
of sexual reproduction. (5 points)
Answer:
Answers will vary. Students should recognize that if meiosis did not occur, the chromosome number
would double with each generation (1 point) and that life could not reproduce due to a fusion of haploid
gametes (1 point). They should also recognize that there would be less genetic variation (1 point), since
crossing over and independent assortment (1 point) are both a part of meiosis. Students may mention
that sexual reproduction drives evolutionary change. Without sexual reproduction and subsequent genetic
variation for natural selection to act upon, evolution has less variation to work on (1 point).
2. Chemotherapy drugs target specific cells in our body. However, there are also side effects to other
body cells during chemotherapy. Explain why these drugs are effective against cancerous cells. What do
you think are the dangers of chemotherapy drugs? Identify other types of cells that are likely to be quick
to divide and therefore to be impacted by chemotherapy drugs. (5 points)
Answer:
Answers will vary. Students should note that cancer cells are targeted by chemotherapy drugs because
cancer cells divide extremely quickly (1 point) due to the fact that they interrupt the cell cycle's natural
shut-off mechanisms (1 point). However, cancer cells are not the only quickly dividing cells in the body, so
chemotherapy is dangerous because it can kill healthy body cells. Chemotherapy also affects hair and
nail cells (1 point), stomach lining (1 point), and immune system cells (lymphocytes) (1 point).
3. Summarize what you learned about the environmental effects on mitosis in your investigations. Which
factors had the largest impact? What data support that conclusion? Were those data statistically
significant? (5 points)
Answer:
Answers will vary. Certain chemicals, such as caffeine, can affect the mitotic division rate. Students
should indicate which variable had the largest impact on division time (1 point), and what that impact
would be (1 point). For example, if they noticed that caffeine increases the cell division rate, then they
should talk about caffeine being a dangerous chemical for cancer patients, since it could increase the
division rate of the cancer cells. Students should also discuss their data for that conclusion (1 point). They
should then give the chi-squared calculations for their data (1 point) to describe whether they are
statistically significant, and whether they are able to accept or reject the null hypothesis (1 point).
4.2.1 Read: Genetics and Gene Expression
AP Biology Sem 1 (S3043799)
Reading Guide
Name: ____________________
Date: ____________
Reading Assignment: Principles of Life (2nd edition)
Please read the following sections of your textbook. As you read, use this reading guide to check your
understanding of the material.
Part
Reading Assignment
Inheritance, Genes, and Chromosomes (8.1 – 8.4)
I
Chapter 8
II
Chapter 11 Regulation of Gene Expression (11.1 – 11.4)
III
Chapter 12 Genomes (12.3)
IV
Chapter 14 Genes, Development, and Evolution (14.1, 14.3, 14.4)
Part I
Compare the following terms:
Gene/Allele: An allele is a form of a gene. For example: Gene = Hair color, Alleles = Brown, blonde, red
Homozygous/Heterozygous: Homozygous individuals possess two dominant or two recessive alleles.
Heterozygous individuals possess one dominant and one recessive allele.
Phenotype/Genotype: A genotype is the combination of alleles an individual has (for example, GG, Gg, or
gg), whereas a phenotype is the expression of the genotype (for example, tall, short, round, or wrinkled).
Complete dominance/Codominance/Incomplete dominance: In complete dominance, one allele is
dominant over the other allele. In codominance, alleles are expressed independently of each other. In
incomplete dominance, the resulting phenotype is a blend of the traits corresponding to the alleles.
Plasmid/Bacterial chromosome: A plasmid is a small, circular piece of DNA that contains a few dozen
genes. The bacterial chromosome contains the rest of the genome.
How does a monohybrid cross illustrate Mendel’s law of segregation?
In a monohybrid cross, offspring can only receive one allele from each parent. Parents cannot pass on
both alleles for one gene without deleterious effects.
How does a dihybrid cross illustrate Mendel’s law of independent assortment?
In a dihybrid cross, the gametes possess all possible allele combinations. Again, parents can only pass
on one allele for each gene, but the inheritance of one allele is not dependent upon the inheritance of
another allele.
What is the purpose of a testcross?
Individuals who are homozygous dominant or heterozygous possess the same phenotype. By crossing an
individual with a dominant phenotype with an individual with a recessive phenotype (who must be
homozygous recessive), we can predict the genotype of the parent based upon the likelihood of the
offspring produced. If homozygous recessive individuals are produced, the parent must be heterozygous.
How could you determine that genes are linked?

Phenotypic ratios would be different than expected.

Some genes would be inherited together and most of the offspring would show phenotypes matching
those of the parents.
This is due to the fact that some genes don't assort independently. Recombinant phenotypes are due to
the fact that two homologous chromosomes physically exchange genetic information during meiosis
(crossing over) so that each chromatid ends up with genes from both of the organism's parents.
What is the significance of a recombination frequency in terms of gene mapping?
The farther apart the loci are, the greater the chance of recombination.
Describe the mechanism of recombination in prokaryotes.
In bacteria, a sex pilus can cause two bacteria to come close together. Once this happens, a conjugation
tube forms and DNA can be transferred from one bacterium to another. The DNA that is exchanged can
be incorporated into the linear DNA of the bacteria. Note the image on page 161.
Part II
Describe how gene expression can be positively regulated or negatively regulated.
Protein synthesis can either be inhibited (prevented) or stimulated. The binding of a repressor near the
promoter region of a gene will stop transcription and therefore negatively impact gene expression. If an
activator is bound to the gene, then positive gene expression will occur. These regulatory proteins
(repressors and activators) are called transcription factors and they determine which genes are
transcribed and which are not.
In the space below, draw the lac operon, labeling the promoters, operator, repressor, and structural
genes.
Students should draw an image similar to figure 11.7 on page 213.
Explain the difference between an inducible operon and a repressible operon.
In an inducible operon, like the lac operon, transcription can be turned on when there is a need for the
product. In a repressible operon, like the trp operon, transcription can be blocked when there is ample
product.
Describe the TATA box.
The TATA box, composed primarily of A-T pairs, is the most common eukaryotic promoter sequence.
Compare DNA methylation and histone protein modification.
DNA methylation and histone protein modification both alter the rate of transcription. During DNA
methylation, the DNA is chemically modified by the addition of a methyl group. This heritable change
causes the silencing of methylated genes. During histone protein modification, positively charged histone
proteins wrap around the DNA, and these nucleosomes make DNA physically inaccessible to RNA
polymerases. Therefore transcription ceases.
Gene expression can also be modified after transcription. Describe the process of alternative splicing.
Pre-mRNA segments can be spliced differently in different cells of the body. Therefore, different proteins
(and combinations of proteins) can be made in different cells of the body. Groups of proteins with different
functions can be created from a single gene.
Identify the three main ways that translation of eukaryotic mRNA can occur:

miRNA

Formation of a 5' cap

Translational repressors
Explain the main differences between eukaryotic and prokaryotic genomes.

Size: Eukaryotic genomes are much larger.

Regulation: Eukaryotes contain more regulatory sequences.

Coding: Eukaryotic DNA contains a lot of noncoding regions and repeated sequences.
In the space below, define each type of stem cell and describe its location in the body.
Type of stem cell
Function
Multipotent
Multipotent describes cells that can form a limited
number of types of differentiated cells.
Pluripotent
Pluripotent describes cells that can individually give
rise to an organism. They are found in the earliest
embryos or are induced.
Explain pattern formation.
In pattern formation, tissues need to know where they're located in relation to one another and need to
ensure that the correct genes are expressed.
Describe the function of organ identity genes.
Some genes encode proteins that work together to cause specific gene expression.
Describe loss of function and gain of function mutations.
Mutations in one combinatorial gene cause no gene expression in a loss of function mutation. If a
promoter for one combinatorial gene can be linked to another combinatorial gene, there can be an
increase, decrease, or different pattern of gene expression.
Explain the function of hox genes.
Hox genes determine patterns of organ and tissue location. Cells in different regions of the body
differentiate in unique patterns.
Describe the function of genetic switches.
Genetic switches include promoters, enhancers, associated proteins, and transcription factors. They
determine when a gene is turned on and when it is turned off. There are many switches — switches for
each gene, at each time, and in each place.
In the space below, draw an image that shows how hox regulatory genes have similar expression
patterns.
Students should draw an image in which a specific gene sequence is matched to specific body segments
on an organism — for instance, mouse, drosophila, and so on, as on page 279.
Explain how specific body structures, including wings, may have evolved by changes in how genes were
expressed.
Gain of function or loss of function mutations in homeotic genes could have caused the changes seen in
the evolution of wings, as shown in figure 14.20.
Key Terms
As you come across these terms during your reading, write your own definition in the space provided.
Key Terms
As you come across these terms in your reading, write your own definitions in the spaces provided.
Parental generation
The individuals that contribute gametes in the first cross in a series of genetic crosses.
First filial generation
The first generation of offspring in a series of genetic crosses; offspring of the parental generation.
Second filial generation
The second generation of offspring in a series of genetic crosses; offspring of crosses among the first filial
generation.
Dominant
Describes an allele that is expressed in the phenotype of a heterozygote.
Recessive
Describes an allele that is not expressed in the phenotype of a heterozygote.
Allele
A version of a gene.
Homozygous
Having two identical alleles for a given trait.
Heterozygous
Having two different alleles for a given trait.
Phenotype
The observable appearance of an organism, resulting from the combination of genetic characteristics and
the environment.
Genotype
The combination of versions of a gene (called alleles) in an organism.
Testcross
A cross between an individual with a dominant phenotype and an individual with a recessive phenotype,
used to identify the genotype of the individual with the dominant phenotype.
Monohybrid cross
A cross between individuals differing in one genetic character.
Dihybrid cross
A cross between individuals differing in two genetic characters.
Independent assortment
The independent segregation (with a gamete's two alleles for two genes coming from the same
chromosome or coming from different chromosomes by random chance) of the alleles of two or more
genes into different gametes.
Pedigree
A diagram of familial relationships with indications of phenotypes that is used to identify the mode of
inheritance of a genetic character.
Wild type
Describes the most common allele or phenotype in nature for a character.
Mutation
A change in genetic material. Mutations range from change in a single nucleotide to rearrangements of
chromosomes to gain or loss of chromosomes or chromosome sets.
Codominance
Describes alleles that are both expressed in the phenotype of a heterozygote.
Incomplete dominance
Describes alleles that interact to express an intermediate phenotype in a heterozygote.
Hybrid vigor
The phenomenon of increased growth, survivorship, or fertility of individuals produced from a cross
between parents from two different inbred lines.
Genetic linkage
The tendency of the alleles of two genes to be inherited together because the genes reside near each
other on the same chromosome.
Recombination frequency
The number of recombinant offspring divided by the total number of offspring from a testcross of the
F1progeny produced from a dihybrid cross.
Hemizygous
Describes the genotype of any trait located on a sex chromosome, which therefore exists in only one
copy in the cells of the individual.
Sex-linked inheritance
The inheritance pattern of genes located on one of the sex chromosomes. Recessive traits tend to appear
more often in the phenotypes of the heterogametic sex (e.g., males, XY, in mammals), because traits on
the sex chromosome are hemizygous.
Transcription factor
A protein that binds to a specific sequence of DNA and regulates transcription either by stimulating it or
blocking it.
Operon
A set of enzyme-coding genes that are normally transcribed together and that are associated with a
single operator sequence, which is capable of binding a repressor protein, and with a promoter sequence,
which binds RNA polymerase when the repressor is not present. Operons are important in prokaryotic
gene expression. Operons have also been found in eukaryotic genomes.
Structural gene
A gene that codes for the amino acid sequence of a protein.
Epigenetic
Describes inheritance mechanisms that do not alter DNA sequences, such as chromatin modification.
Histone
A protein that is used in packaging DNA molecules.
Alternative splicing
Producing different proteins from one pre-mRNA transcript by forming different combinations of exons.
microRNA
Small RNA molecules that have a role in regulating gene expression at translation by binding with and
degrading mRNA or preventing translation.
Bacterial conjugation
The transfer of DNA between two cells joined by a pilus.
Transposon
A sequence of DNA that moves from one location in a genome to another, or copies itself and inserts the
copy in a new location in a genome. The transposon typically contains genes for enzymes that allow for
its own movement.
Gene families
Sets of genes that have similar sequences but different, though usually related, functions. Gene families
arise through duplication and subsequent evolution of new functions.
Single nucleotide polymorphisms (SNPs)
Differences between alleles in a population caused by differences in individual nucleotides.
Short tandem repeats (STRs)
DNA sequences consisting of fewer than 10 nucleotides repeated many times immediately adjacent to
each other. Their high mutation rates make short tandem repeat sequences excellent identifiers of
individuals, and they are used in forensic identification and genealogy.
Organ identity genes
Hox genes in floral development; genes that define the different parts of the flower.
Hox genes
A group of homeobox genes that code for regulatory proteins that are expressed in different parts of the
developing embryo and signal to developing tissues their location within the embryo.
Homeobox
A highly conserved DNA sequence (present in plants, animals, and fungi) that codes for protein regions
that bind DNA and that is thus involved in regulating transcription and that usually controls genes
affecting anatomical development.
Genetic switches
A recognition sequence and associated regulatory protein that control the transcription of a gene.
Totipotent
Describes a single cell that has the ability to give rise to cells that can differentiate into any cell type in a
multicellular organism.
Plasmid
A circular DNA molecule common in prokaryotes that is often used as a vector for recombinant DNA.
4.2.3 Study: Probability Demonstrations and Punnett
Squares
AP Biology Sem 1 (S3043799)
Study Sheet
Name: ____________________
Date: ____________
As you read through the study, use this study sheet to help you organize your thoughts.
Distinguish between phenotype and genotype, and give an example of each.
A genotype is the unique combination of alleles found at one or more gene loci. A phenotype is the
expression of that genotype or the observable features in an organism, such as pea shape.
In pea plants, smooth seeds are dominant to wrinkled seeds. If two pea plants that are heterozygous for
the smoothness gene are crossed, what proportion of their offspring will have smooth seeds?
Ss x Ss = 3 (smooth):1 (wrinkled); ¾ of the offspring will have smooth seeds.
Why do human X-linked recessive traits appear in the phenotypes of males more often than in the
phenotypes of females?
Many more males than females express X-linked recessive traits, as males have only one X
chromosome, and females have two Xs. Thus, males need only a single allele to show the recessive
condition; they don't have another X to offset the condition.
Inheritance patterns may follow simple Mendelian principles or may be more complex than predicted by
simple Mendelian genetics. In the chart below, distinguish the inheritance patterns by writing Mendelian
trait or Non-Mendelian trait in the column on the right.
Draw lines matching the main ideas of this study with the four Big Ideas of AP Biology. For each main
idea, explain how it is related to the Big Idea.
4.2.5 Study: Pedigree Analysis of Human Genetic
Disorders
AP Biology Sem 1 (S3043799)
Study Sheet
Name: ____________________
Date: ____________
1. What is the initial question you are trying to answer?
Question
What is the mode of inheritance for each disease?
2. Is there an initial prediction you can make about the question you've been asked? What information
leads you to make that prediction? Write your prediction in the table below and explain the justifications
for your prediction.
Initial prediction
Justification
"I can make this prediction because..."
My prediction is that each disease will follow
Mendel's rules and be either dominant or
recessive.
Dominant and recessive are two common types of
inheritance.
3. What questions do you have right now? What are you hoping the next section explains to you?
I'm unsure of how to analyze pedigrees. I'm hoping the next section will explain how to use them. I'm also
not sure what all the symbols and lines refer to and what it means to see a circle or square filled in.
4. As you read through the study, record the evidence that you are given that could help you answer the
question.
Evidence
Significance of the evidence
"This evidence is important because..."
In the De Luca family, both males and females
can be afflicted with the disease.
The gene for the disease is probably not carried
on a sex chromosome.
Frederica does not have the disease, but both of
her parents did.
This shows that the disease could not be
recessive. If it were, Frederica's parents would
beaa, and so would she. Therefore, she would
have the disease.
Dina's father must be heterozygous (Aa), while
her mother is homozygous (aa).
This reveals that Dina's odds of inheriting the
disease are 50%.
In the Torres family, the disease only appears in
males.
This reveals that it is probably on a sex
chromosome.
In the Torres family, the trait is passed from
unafflicted mothers to their sons.
This reveals that the trait is X-linked recessive.
In the Williams family, inherited blindness is
passed from mothers to both their sons and
daughters.
This reveals that the disease is mitochondrial.
5. What conclusions did you draw at the end of the study?
Pedigrees are really useful tools for studying how human diseases are inherited.
6. Congratulations on solving the mystery!! As you look back on the case study, were there additional
clues that you missed? If so, how would they have helped you to make your final prediction more
accurate?
Yes, I missed the clue in the De Luca family that the disease doesn't skip generations. If I had realized
what that meant, I probably would have decided it was a dominant disease sooner.
7. Are there additional clues that could have been provided that would have been helpful to you without
giving away the answer to the questions?
No, I think the case study did a good job of giving clues without giving away the answer.
4.2.7 Practice: Genetics and Gene Expression
AP Biology Sem 1 (S3043799)
Practice Assignment
Name: ____________________
Points possible: 25
Date: ____________
1. A woman buys seeds for an annual flowering plant. After planting the seeds in her garden, she is
happy to see that all of them produce red flowers. She collects the seeds produced by the flowers at the
end of the season and stores them over the winter. When she plants them the next spring, she is
surprised to find that 8 plants produced white flowers and 32 plants produced red flowers. Explain this
outcome by comparing the observed numbers of white and red flowering plants to those expected if the
following conditions are assumed:

The plants are self-pollinating (that is, seeds are only produced by crosses between plants in the
garden).

The flower color trait results from two alleles, one dominant and the other recessive.
(3 points)
Answer: The seeds that were purchased were heterozygous for the red and white flower alleles. The
plants all had red flowers because red flower color is dominant. However, because all of the plants
carried both alleles, a cross resulted in the following distribution:
25% AA, 50% Aa, 25% aa
A
a
A
AA
Aa
a
Aa
aa
The red phenotype shows up approximately 75% of the time, corresponding to the sum of 25% AA +
50% Aa. The white phenotype only shows up 25% of the time. These percentages correlate reasonably
well with the observed frequencies of these two phenotypes in the population: 32/40, or 80%, red and
8/40, or 20%, white.
2. A human needs at least one functional allele for a particular protein in order to have normal metabolic
behavior. A man and a woman marry and produce 8 children. Neither parent has the metabolic disorder
related to the protein described above, but 3 of their children do. Explain the most likely pattern of
inheritance, based on the data below. (3 points)
Family Member
Normal metabolism
Father
✓
Mother
✓
Daughter 1
✓
Daughter2
✓
Metabolic disorder
✓
Son 1
✓
Son 2
✓
Son 3
Son 4
✓
Son 5
✓
✓
Son 6
Answer: If this disease is an autosomal recessive, any children with the disorder must have inherited two
mutant alleles, assuming that the gene follows normal Mendelian patterns of inheritance. That means that
both parents would have to be heterozygous. In that case, only 25% of their children would be likely to
inherit a mutant allele from each parent and suffer from the disease. However, half of the children have
the disease, and, in addition, the disease appears to be limited to sons. These pieces of information
suggest that the gene is located on the X chromosome, and that the mother carries the mutant allele. In
this case, each son would have a 50% chance of receiving the mutant allele, which would cause him to
suffer from the disease.
XA
XA
XAXA
(normal female)
Xa
XAXa
(normal female)
Y
XAY
(normal male)
XaY
(afflicted male)
3. The following table shows the results of a breeding experiment to study the inheritance of flower color
and grain length in plants, two genes that exhibit complete dominance in phenotypes. True-breeding
parent plants with purple flowers and long pollen grains were crossed with true-breeding parent plants
with red flowers and short pollen grains. A second experiment was also conducted between members of
the F1 generation to produce an F2 generation. The phenotypes of the resulting offspring in the F1 and
F2 generations are in the figure
below.
a. Using the data in the table, identify the dominant alleles for flower color and grain length. Explain your
response. (3 points)
A Punnett-square analysis provides a way to predict the expected outcome of the cross of a true-breeding
dominant strain of both alleles (AABB) with a true-breeding recessive strain of both alleles (aabb). The
square below shows that 100% of the offspring of the cross described will have a phenotype expressing
both dominant traits. Since 100% of the F1 offspring were purple with long grains, purple is dominant to
red, and long is dominant to short.
AB
AB
Ab
AaBb
AaBb
Ab
AaBb
AaBb
b. Analyze the distribution of phenotypes in the F2 generation. Explain whether the observed results
match those expected based upon the results of the first cross. (3 points)
Answer: The observed phenotypic ratios do not match the expected phenotypic ratios derived from the
Punnett-square analysis below. The phenotypic ratio observed is close to 6:1:1:3, while the Punnett
square predicts a ratio of 9:3:3:1. This is not a Mendelian pattern of inheritance, which means that some
Mendelian assumption is not holding in this case. One possibility is that the traits of flower color and
pollen size do not sort independently. If the two traits are located on the same chromosome, they would
tend to sort together, as is observed here — the highest numbers of offspring have both traits of the
parents.
AB
Ab
aB
ab
AB
AABB
AABb
AaBB
AaBb
Ab
AABb
AAbb
AaBb
Aabb
aB
AaBB
AaBb
aaBB
aaBb
ab
AaBb
Aabb
aaBb
aabb
Expected phenotypic ratios: Purple, long: AABB + 2AABb + 2AaBB + 4AaBb = 9
Purple, short: AAbb + 2Aabb = 3
Red, long: aaBB + 2aaBb = 3
Red, short: aabb = 1
4. Wild fruit flies have a gray body, red eyes, and long wings. The three genes for these traits are all
located on the same chromosome. Each gene has a normal, dominant allele and a mutant allele that
gives rise to a different, recessive trait. The mutant traits are a black body (b), cinnabar eyes (cn), and
vestigial wings (vg). The normal, dominant alleles are indicated with a plus-sign superscript — gray body
(b+), red eyes (cn+), and long wings (vg+). The table below shows the results of two testcrosses involving
dihybrids with two of the three mutant traits.
Use the data from the two testcrosses to roughly sketch a chromosome and map the locations of the
three genes. Then, write a couple of sentences that justify your chromosome map. (3 points)
Answer:
1 point: The chromosome map can be sketched as follows:
1 point: The greater the distance between genes on a single chromosome, the greater the chance for
crossing over to occur and the greater the number of recombinants that will result among the offspring.
1 point: Therefore, the larger percentage of recombinants in the first testcross indicate that there is a
greater distance between the genes for eye color (w) and wing size (m) than between the genes for eye
color (w) and body color (y).
5. A study was conducted to examine the influence of vitamin A on gene expression in developing fish
larvae. Fish larvae were divided into control and experimental groups. The control group received a
complete diet; the experimental group received a complete diet minus vitamin A. Larvae from the
experimental group did not demonstrate the same pattern of gene expression at different stages during
development that was observed in larvae from the control group. At the end of the study, experimental
larvae showed signs of skeletal deformities that were not observed in the control group.
a. Explain the relationship between vitamin A and normal development. (2 points)
Answer: Vitamin A appears to be a factor in normal gene expression controlling the development of
skeletal characteristics.
b. Describe how the process of gene expression can affect the development of specialized structures
such as bones. (2 points)
Answer: Gene expression in cells is coordinated by a series of chemical messages coming from other
cells in the organism and from the external environment. As the organism develops, its cells respond to
these chemical messages. Cells shift their metabolism over time to take in various nutrients from the
environment in response to shifting chemical messages. Development proceeds normally if the pattern of
genes turning on and off is not disrupted and if all of the necessary nutrients are present to supply the
building blocks for each different stage.
6. Researchers studied the effects of atrazine, a herbicide, on developing frog larvae. They found that
administration of atrazine did not affect the frog’s life span or its overall health. Atrazine also had no
observable effect on female frog larvae. However, atrazine did convert the male larvae into
hermaphrodites — organisms with both male and female sex organs — capable of producing viable eggs.
a. Describe how gene expression differs during the normal process of sexual differentiation in animals. (2
points)
Answer: During normal development, hormones cause the expression of different patterns of genes in
males and females. These hormones signal cells to express specific genes needed for sexual
development. This leads to the observed differences in sex organs and mating behaviors of the two
sexes.
b. Explain a possible mechanism for atrazine's effect on developing male frogs. (2 points)
Answer: The pattern of hormone expression is specific to each sex. Therefore, if a new chemical
compound is introduced that mimics a hormone, the cells will respond as if the hormone was present.
Atrazine must mimic a female hormone, because it induces the expression of genes that lead to the
development of female traits in males, but it does not affect the development of females.
7. Explain how regulation of gene expression allows a cell to efficiently use its energy supply to carry out
specific metabolic reactions that are necessary at specific times. (2 points)
Answer: The cell has the capability of carrying out a vast array of metabolic reactions. However, the
energy requirements the cell would need to carry out all of these reactions at once would far exceed its
normal energy reserves. Instead, the cell only carries out the reactions needed at each moment in time,
which is a small subset of its total capacity. In order to limit this subset, the cell regulates the expression
of genes that code for enzymes and other proteins needed for metabolic reactions. By only expressing
those genes needed for carrying out processes of immediate importance, the cell efficiently uses the
energy available to it.
4.2.8 Explore: Embryonic Stem Cells and Gene
Expression
AP Biology Sem 1 (S3043799)
Points possible: 25
Exploration
Name: ____________________
Date: ____________
1. Explain the similarities and differences of embryonic stem (ES) cells and organ-specific stem cells. (4
points)
Ideal Answer: Both cells are classified as stem cells, which means that they are capable of dividing to
generate new cells that can then go on to differentiate into specialized cells. The difference is that organspecific stem cells have already undergone partial differentiation and cannot change their path of
differentiation. Organ-specific stem cells are restricted to being able to generate new cells with
specializations associated with the organ they come from. In contrast, embryonic stem cells have not
undergone any differentiation and are able to be used for the formation of any type of differentiated cells.
Score: 2 points for explaining the similarities between the two types of stem cells, and 2 points for
explaining their differences.
2. Some people object to the use of embryonic stem (ES) cells for scientific study or for medical
applications. One of the objections raised concerns the ethics of sacrificing embryonic cells. People with
this objection think that cells that could potentially become a human should not be used for any other
purpose.
a. Based upon this information, explain why organ-specific stem cells do not elicit the same objections. (3
points)
Ideal Answer: Organ-specific stem cells are not totipotent and are therefore, not capable of being used for
organismal cloning. These stem cells do not require the extraction from a sacrificial human embryo which
is potentially, or actually, depending on your point of view, a human being.
Score: 1 point for recognizing that these cells are not totipotent. 1 point for identifying that embryonic
stem cells require the sacrifice of a human embryo. 1 point for identifying that organ-specific stem cells do
not require this sacrifice.
b. Would your answer to part a, above, change if recent studies are confirmed claiming that organspecific stem cells can be converted into totipotent cells? Explain your reasoning. (3 points)
Ideal Answer: Yes, my answer would change. Theoretically such stem cells could be used to develop into
a full human being, and so that potential would be sacrificed if they were used for any other reason. It
seems that if a person objected to stem cells on this basis, then they would object to using any cell with
such enormous potential for any other purpose.
Score: 1 point for stating an answer of yes or no, and 2 points for providing a thoughtful answer to explain
reasoning behind the answer.
3. Additional ethical questions surround the use of stem cells. For example, some people feel that using
stem cells to cure disease opens the possibility of extending the human life span far beyond the normal
biological limit.
a. Evaluate whether you think it is possible to indefinitely extend human life using stem cells to replace
worn-out cells. (3 points)
Ideal Answer: Yes, I think that eventually, given enough research, scientists should be able to determine
how to replace worn-out cells with fresh cells derived from stem cells. This process should be able to go
on indefinitely as long as there are ways to locate cells that need to be replaced, and there are suitable
replacements and methods for effectively replacing the old with the new cells.
Score: 1 point for stating an answer of yes or no, and 2 points for providing a thoughtful explanation of the
reasoning behind the answer.
b. If stem-cell technology can be advanced to the extent of extending human life indefinitely, is it ethical to
develop such technology? Explain your reasoning. (3 points)
Ideal Answer: No, in my opinion, it is not ethical to extend life indefinitely. Society needs to evolve, which
means that new generations must replace older generations. If one generation was to live forever, there
would be no change and therefore no forward progress. Each generation must accept its place in history
and then relinquish their hold on society to the next generations that come after them.
Score: 1 point for stating an answer of yes or no, and 2 points for providing a thoughtful answer to explain
reasoning behind the answer.
4. What will be gained and what will be lost if stem cells are developed for curing the diseases listed by
the authors in the opening paragraph? Explain your answer. (4 points)
Ideal Answer: There will be many more gains than losses. Many people will have extended lives and/or
better quality of life if stem cells are able to cure diabetes, Parkinson's disease, neurological
degeneration, and congenital heart disease. Society will also gain by avoiding spending a lot of money by
keeping these people functional and out of costly nursing homes and care facilities. The only loss will be
any taxpayer money needed to develop these technologies; however, this money will repay itself in
reduced costs for care.
Score: 2 points for identifying gains and 2 points for identifying losses and providing thoughtful
explanations for each.
5. The authors spend considerable effort to distinguish between reproductive cloning and therapeutic
cloning.
a. Evaluate their intention in making this distinction clear. What do you think the authors hope to gain by
their clarification of terms? (2 points)
Ideal Answer: The authors want the public to understand that therapeutic cloning does not directly lead to
the creation of a new whole organism. They probably hope to promote the use of therapeutic cloning for
medical purposes and want to be sure that the public sees it as a non-threatening technology.
Score: 1 point for differentiating between reproductive and therapeutic cloning and 1 point for recognizing
that the public confuses the two and need to realize that therapeutic cloning will not lead to any
Frankenstein scenarios.
b. Do you think that the authors’ suggestion of clarifying these terms will make a difference to public
reaction about this technology? Are there additional discussions involving the public that need to occur at
the same time that scientists discuss the scientific principles underlying stem-cell biology? Explain your
thinking. (3 points)
Ideal Answer: Yes, I think it is helpful for people to understand the scientific distinction between the two
types of cloning. They are more likely to support the positive uses of such technologies if they understand
their limitations.
Ethical discussions should be part of the development of technologies like stem cell research. These
discussions should be open to anyone so there can be plenty of dialogue to flesh out any potential
problems that scientists may not have considered. Scientists should listen to the rest of society to put a
cap on any work that does not fit society's moral and ethical standards.
Score: 1 point for answering the two questions posed, and 2 points for providing thoughtful explanations
for each.