Download Raven/Johnson Biology 8e

Raven/Johnson Biology 8e
Chapter 18 Answers
1. A genetic map is based on—
a. the sequence of the DNA
b. the relative position of genes on chromosomes
c. the location of sites of restriction enzyme cleavage
d. the banding pattern on a chromosome
The correct answer is b—
A. Answer a is incorrect. The sequence of the DNA is an example of a physical map.
The correct answer is b—the relative position of genes on chromosomes
B. Answer b is correct. Genetic maps are abstract maps that identify the location of genes
and are based on recombination frequency in genetic crosses.
The correct answer is b—
C. Answer c is incorrect. The use of restriction enzymes allows for the construction of a
physical map based on the location of sequences specific to different enzymes.
The correct answer is b—
D. Answer d is incorrect. The banding pattern on a chromosome is an example of a physical
map.
2. What is an STS?
a. A unique sequence within the DNA that can be used for mapping
b. A repeated sequence within the DNA that can be used for mapping
c. An upstream element that allows for mapping of the 3′ region of a gene
d. Both b and c
The correct answer is a—A unique sequence within the DNA that can be used for mapping
A. Answer a is correct. Sequence-tagged sites occur only once within a genome and can be
used to generate physical maps of a chromosome.
The correct answer is a—
B. Answer b is incorrect. Sequence-tagged sites are unique within the genome.
The correct answer is a—
C. Answer c is incorrect. Sequence-tagged sites are unique sequences that occur throughout
the genome.
The correct answer is a—
D. Answer d is incorrect. Sequence-tagged sites are unique sequences that occur throughout
the genome.
3. An artificial chromosome is useful because—
a. It produces more consistent results than a natural chromosome
b. it allows for the isolation of larger DNA sequences
c. it provides a high copy number of a DNA sequence
d. they are linear
The correct answer is b—
Raven/Johnson Biology 8e
Chapter 18 Answers
A. Answer a is incorrect. The value of an artificial chromosome is related to the large size of
DNA fragments that can be inserted into them.
The correct answer is b—it allows for the isolation of larger DNA sequences
B. Answer b is correct. Artificial chromosomes can carry inserts of up to 200 kb of DNA.
The correct answer is b—
C. Answer c is incorrect. Artificial chromosomes are unlike plasmids and are not typically
present in high copy numbers.
The correct answer is b—
D. Answer d is incorrect. Yeast artificial chromosomes (YACs) are linear, but bacterial
artificial chromosomes (BACs) are circular.
4. Which of the following techniques relies on knowledge of overlapping sequences?
a. Radiation hybrid mapping
b. Shotgun method of genome sequencing
c. FISH
d. Clone-by-clone method of genome sequencing
The correct answer is d—
A. Answer a is incorrect. Radiation hybrids can be used to identify overlapping sequences,
but does not require prior knowledge of overlaps.
The correct answer is d—
B. Answer b is incorrect. The shotgun method generates small random fragments, and
overlapping sequences are determined afterward.
The correct answer is d—
C. Answer c is incorrect. FISH can be used to identify positions of cloned genes on
chromosomes.
The correct answer is d—Clone-by-clone method of genome sequencing
D. Answer d is correct. The clone-by-clone method starts with construction of known
overlapping sequences.
5. Which number represents the total number of genes in the human genome?
a. 2500
b. 10,000
c. 25,000
d. 100,000
The correct answer is c—
A. Answer a is incorrect. The human genome has more genes.
The correct answer is c—
B. Answer b is incorrect. The human genome has more genes. Yeast cells have around
10,000 genes.
Raven/Johnson Biology 8e
Chapter 18 Answers
The correct answer is c—25,000
C. Answer c is correct. The estimated number of genes is around 25,000; down from an
estimate of 100,000.
The correct answer is c—
D. Answer d is incorrect. The original estimate for the number of genes in the human
genome was 100,000. More recent evidence supports a number closer to 25,000.
6. An open reading frame (ORF) is distinguished by the presence of—
a. a stop codon
b. a start codon
c. a sequence of DNA long enough to encode a protein
d. all of the above
The correct answer is d—
A. Answer a is incorrect. A stop codon is a required part of a gene, but there must be other
regions present before a DNA sequence can be called a gene.
The correct answer is d—
B. Answer b is incorrect. All genes begin with a start codon; however, there is more to a
gene.
The correct answer is d—
C. Answer c is incorrect. For a gene to encode a protein a piece of DNA sequence of
sufficient length is needed (remember three nucleotides encode one amino acid).
The correct answer is d—all of the above
D. Answer d is correct. All of these components must be present if a sequence of DNA is to
be suspected of being a gene.
7. What is a BLAST search?
a. A mechanism for aligning consensus regions during whole-genome sequencing
b. A search for similar gene sequences from other species
c. A method of screening a DNA library
d. A method for identifying ORFs
The correct answer is b—
A. Answer a is incorrect. BLAST is a computer algorithm that helps scientist look for similar
genes in other species.
The correct answer is b—A search for similar gene sequencing from other species
B. Answer b is correct. BLAST is a computer algorithm that identifies sequence similarities
and aligns similar sequences.
The correct answer is b—
C. Answer c is incorrect. BLAST is a computer algorithm that helps scientists look for
similar genes in other species. It requires a cloned DNA that has already been isolated.
The correct answer is b—
Raven/Johnson Biology 8e
Chapter 18 Answers
D. Answer d is incorrect. BLAST is a computer algorithm that helps scientists look for
similar genes in other species; it does not identify ORFs.
8. Which of the following is NOT an example of a protein-encoding gene?
a. Single-copy gene
b. Tandem clusters
c. Pseudogene
d. Multigene family
The correct answer is c—
A. Answer a is incorrect. Single-copy genes are one form of protein-encoding genes.
The correct answer is c—
B. Answer b is incorrect. Tandem clusters are identical genes that are transcribed all at one
time.
The correct answer is c—Pseudogene
C. Answer c is correct. A pseudogene is one that is no longer expressed.
The correct answer is c—
D. Answer d is incorrect. Multigene families are groups of related genes.
9. The duplication of a gene due to uneven meiotic crossing over is thought to lead to the
production of a—
a. segmental duplication
b. tandem duplication
c. simple sequence repeat
d. multigene family
The correct answer is b—
A. Answer a is incorrect. A segmental duplication occurs when large blocks of genes are
shared between nonhomologous chromosomes.
The correct answer is b—tandem duplication
B. Answer b is correct. A tandem cluster can arise by unequal crossing over.
The correct answer is b—
C. Answer c is incorrect. Simple-sequence repeats are thought to occur due to DNA
replication errors.
The correct answer is b—
D. Answer d is incorrect. Multigene families can arise by unequal crossing over but can arise
by other mechanisms as well.
10. Which of the following is NOT an example of noncoding DNA?
a. Promoter
b. Intron
c. Pseudogene
d. Exon
Raven/Johnson Biology 8e
Chapter 18 Answers
The correct answer is d—
A. Answer a is incorrect. Promoters do not encode protein; rather they acts as recognition
sites for RNA polymerase.
The correct answer is d—
B. Answer b is incorrect. Introns are the sequences that are removed from the mRNA during
posttranscriptional processing.
The correct answer is d—
C. Answer c is incorrect. A pseudogene is an inactive gene.
The correct answer is d—Exon
D. Answer d is correct. Exons correspond to the DNA sequences that are expressed as
protein.
11. Comparisons between genomes is made easier because of—
a. synteny
b. haplotypes
c. transposons
d. expressed sequence tags
The correct answer is a—synteny
A. Answer a is correct. Synteny refers to the idea that the location and arrangement of genes
within a chromosome is conserved; so knowledge of one genome allows for predictions
about other genomes.
The correct answer is a—
B. Answer b is incorrect. Haplotypes are regions of a chromosome that are not exchanged
during meiosis. A haplotype contributes to the mapping of genes within a species.
The correct answer is a—
C. Answer c is incorrect. Transposons, or transposable elements, are regions of DNA that are
capable of changing their location within the genome.
The correct answer is a—
D. Answer d is incorrect. Expressed sequence tags (ETS) are made from mRNA that is
expressed. This allows the mapping of transcripts within a species but does not help with
comparisons between species.
12. What information can be obtained from a DNA microarray?
a. The sequence of a particular gene
b. The presence of genes within a specific tissue
c. The pattern of gene expression
d. Differences between genomes
The correct answer is c—
A. Answer a is incorrect. A DNA microarray provides information on the pattern of gene
expression, not the sequence of genes.
Raven/Johnson Biology 8e
Chapter 18 Answers
The correct answer is c—
B. Answer b is incorrect. The DNA microarray is only sensitive to the presence or absence
of an mRNA, not DNA.
The correct answer is c—The pattern of gene expression
C. Answer c is correct. DNA microarray technology uses fluorescent probes to examine the
pattern of gene expression in various samples.
The correct answer is c—
D. Answer d is incorrect. A DNA microarray provides information on the pattern of gene
expression, not the content of genomes.
13. Which of the following is true regarding microarray technology and cancer?
a. A DNA microarray can determine the type of cancer.
b. A DNA microarray can measure the response of a cancer to therapy.
c. A DNA microarray can be used to predict whether the cancer will metastasize.
d. All of the above.
The correct answer is d—
A. Answer a is incorrect. Microarrays can be used to identify the form of cancer based on
patterns of gene expression; however, the technology has broader applications.
The correct answer is d—
B. Answer b is incorrect. Microarrays can be used to determine the effectiveness of
therapies; however, the technology has broader applications.
The correct answer is d—
C. Answer c is incorrect. Microarrays allow for prediction about the likelihood of a cancer
metastasizing; however, the technology has broader applications.
The correct answer is d—All of the above.
D. Answer d is correct. The power of DNA microarray technology is that it provides an
insight into gene expression of a cancer cell and gene expression is the factor that controls
the behavior of cells.
14. What is a proteome?
a. The collection of all genes encoding proteins
b. The collection of all proteins encoded by the genome
c. The collection of all proteins present in a cell
d. The amino acid sequence of a protein
The correct answer is b—
A. Answer a is incorrect. The proteome represents proteins, not genes. Recall that in some
cases a single gene can produce multiple distinct proteins through alternative splicing.
The correct answer is b—The collection of all proteins encoded by the genome
Raven/Johnson Biology 8e
Chapter 18 Answers
B. Answer b is correct. A cell’s proteome is the entirety of proteins expressed. In a
multicellular organism the proteome for any one cell type would not represent the entire
proteome.
The correct answer is b—
C. Answer c is incorrect. A proteome represents all proteins coded for by the genome. Recall
that not all proteins are expressed at the same time.
The correct answer is b—
D. Answer d is incorrect. A proteome represents all proteins coded for by the genome.
15. Which of the following techniques could be used to examine protein–protein interactions
in a cell?
a. Two-hybrid screens
b. Protein structure databases
c. Protein microarrays
d. Both a and c
The correct answer is d—
A. Answer a is incorrect. The two-hybrid system does allow for the identification of proteinprotein interactions; however, it is not the only example.
The correct answer is d—
B. Answer b is incorrect. Protein structure databases are used for predicting protein structure
based on gene sequences.
The correct answer is d—
C. Answer c is incorrect. Protein microarrays can be used to probe for protein–protein
interactions; however, it is not the only example.
The correct answer is d—Both a and c
D. Answer d is correct. Both two-hybrid screens and protein microarrays can be used to
identify protein–protein interactions.
Challenge Questions
1. You are in the early stages of a genome-sequencing project. You have isolated a
number of clones from a BAC library and mapped the inserts in these clones using
STSs. Use the STSs to align the clones into a contiguous sequence of the genome (a
contig).
Raven/Johnson Biology 8e
STS 3
Chapter 18 Answers
STS 4
STS 5
Clone A
STS 2
STS 3
Clone B
STS 5
STS 6
Clone C
STS 3
STS 4
Clone D
STS 1
STS 2
Clone E
Answer——The STSs represent unique sequences in the genome. They can be used to align the
clones into one contiguous sequence of the genome based on the presence or absence of an STS
in a clone. The contig, with aligned clones, would look like this:
STS 1
STS 2
Clone E
STS 2
STS 3
Clone B
STS 3
STS 4
STS 3
STS 4
STS 5
Clone A
Clone D
STS 5
STS 6
STS 5
STS 6
Clone C
STS 1
STS 2
STS 3
STS 4
Contig
2. Genomic research can be used to determine if an outbreak of an infectious disease is
natural or “intentional.” Explain what a genomic researcher would be looking for in a
suspected intentional outbreak of a disease like anthrax.
Answer—The anthrax genome has been sequenced. Investigators would look for differences in
the genome between existing natural strains and those collected from a suspected outbreak. The
genome of an infectious agent can be modified, or “weaponized,” to make it more deadly. Also,
single-nucleotide polymorphisms could be used to identify the source of the anthrax. In the case
of the Florida anthrax outbreak it was determined that the source was a research laboratory.