Chapter 21—Evolution at the Molecular Level
Fill in the Blank
1. Charles Darwin published his theory of evolution in his book called
__________________in 1859.
Ans: The Origin of Species
Difficulty: 1
2. One of the cornerstones of Darwin's theory of evolution known as the process of
_____________, states that some variant traits confer on some individuals a greater
chance of surviving and reproducing while other traits reduce fitness.
Ans: natural selection
Difficulty: 1
3. Darwin understood that inheritance was a factor in evolution but his understanding of
this process was limited because he did not read Mendel's paper,
entitled_______________________, which was published in 1866.
Ans: Experiments on Plant Hybrids
Difficulty: 2
4. The populations of T and B lymphocytes that circulate throughout vertebrate blood and
tissues have the genetic ability to synthesize a great variety of
___________________________________, which are protein molecules that can
recognize non-self antigens from self antigens.
Ans: cell surface immune receptors
Difficulty: 2
5. The HIV viral genome experiences rapid mutation and subsequent evolution due to the
replicative infidelity of the enzyme ________________________________ which
converts viral RNA into double stranded ________ in infected cells.
Ans: reverse transcriptase, cDNA
Difficulty: 2
6. The fatal consequences of untreated HIV infection result from the rapid accumulation of
billions of mutant virus strains in an infected individual which subsequently out paces
the ability of the hosts _________________________________ to control.
Ans: immune system
Difficulty: 2
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7. The three basic components of molecular evolution are
___________________________ to produce genetic variants,
____________________________ of a favored subset of variants and the
______________________________ of the favored variants in a population over many
generations.
Ans: diversification, selection, amplification
Difficulty: 3
8. All living cells capable of reproduction utilize ________________ as the genetic
material while non-living viruses can have _________________________ genomes.
Ans: DNA, DNA or RNA
Difficulty: 2
9. Some RNA molecules have been identified as being capable of carrying out enzymatic
reactions involving intron removal and are known as __________________, a term
denoted by the discoverers T. Cech et al.
Ans: ribozymes
Difficulty: 2
10. In a primordial world, a major disadvantage to having RNA serve as the repository of
genetic information is the molecules susceptibility to _______________ and
____________________ hydrolysis.
Ans: chemical, enzymatic
Difficulty: 3
11. Mutations which are selectively neutral either survive or are eliminated from
populations by the process of _____________________ which results primarily of
chance events during reproduction.
Ans: genetic drift
Difficulty: 2
12. An advantageous allele becomes _________________________ when it becomes
present in more than 99 percent of the sum total of the loci present in a population.
Ans: fixed
Difficulty: 2
13. Genome size in eukaryotes has increased primarily by the processes of
___________________ and ________________________ of DNA sequences as new
DNA arises from pre-existing sequences.
Ans: duplication, diversification
Difficulty: 3
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14. Duplications of chromosomal DNA sequences can naturally arise via two mechanisms
called ______________, a type of chromosomal aberration, and
___________________, which is a form of illegitimate recombination.
Ans: transposition, unequal crossing over
Difficulty: 3
15. The existence of pseudogenes that have string of polyadenylic acid residues at their 3'
end is indicative of integration of a cDNA copy of an RNA transcript produced by the
action of the enzyme ________________________________ which is encoded by
________________________ sequences present in the genome.
Ans: reverse transcriptase, retroviral
Difficulty: 3
16. Transposition is defined as the movement of a ___________________________ copy of
a chromosomal DNA sequence to a location on another non homologous chromosome.
Ans: duplicated
Difficulty: 2
17. Normal meiotic crossing over occurs during the ______________________ stage of
prophase I and is mediated by a cytological structure called the
________________________.
Ans: pachytene, synaptonemal complex
Difficulty: 3
18. In Drosophila, the normal non-Bar eye, Bar eye, and Ultrabar phenotypes result from
____________________ and the Bar eye phenotype results from _______ copies of the
Bar eye locus.
Ans: Unequal crossing over, two
Difficulty: 4
19. Non functional copies of normally expressed genes called
_________________________ arise via random genetic drift and accumulate mutations
at a faster rate than functional coding or regulatory sequences.
Ans: pseudogenes
Difficulty: 2
20. A duplicated copy of an ancestral vertebrate beta globin gene gave rise to an oxygen
storage protein called ___________________ which is normally expressed in
_____________________ tissue and is functionally monomeric.
Ans: myoglobin, muscle
Difficulty: 3
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21. The two types of T-cell receptors, called ____________ and _____________, are
encoded by three gene families and the generation of T-cell receptor diversity is similar
to the process that generates antibody diversity except that
________________________________ does not occur.
Ans: alpha/beta, gamma/delta, somatic hypermutation
Difficulty: 3
22. The _______________ portion of the human beta T-cell receptor has been duplicated
and translocated to chromosome 9 and contains __________ V gene segments and one
functional _________________________ gene.
Ans: 3', 7, transposition
Difficulty: 3
Multiple Choice
Select all that apply
23. Triple drug therapy to arrest HIV infection is designed to specifically inhibit:
a. DNA polymerases
b. reverse transcriptase
c. proteases
d. endonucleases
e. peptidyl transferase
Ans: b, c
Difficulty: 2
24. A small subset of immune cells called ________________ can persist long past the
initial immune response in humans. They arise during the T and B cell clonal expansion
and proliferation in response to antigen stimulation.
a. effector cells
b. CD4 cells
c. memory cells
d. macrophages
e. T-helper cells
Ans: c
Difficulty: 2
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25. The Burgess Shale, which contains the earliest representation of all the phyla in current
existence, was deposited around ___________________ years ago.
a. 1.4 million
b. 2.3 billion
c. 1 billion
d. 700 million
e. 4.2 billion
Ans: d
Difficulty: 2
26. It is believed that the mass extinction which led to the dinosaurs demise around 65
million years ago was the result of a large asteroid impact near present day:
a. Iceland
b. Hawaii
c. Siberia
d. Manitoba
e. Yucatan
Ans: e
Difficulty: 1
27. In an ideal primordial RNA world, multi functional RNA molecules would be required
to have which of the following properties?
a. fold into three dimensional structures with enzymatic capabilities
b. carry out selective self replication
c. synthesize double stranded DNA
d. phosphorylate proteins
e. encode genetic information in a four letter digital alphabet
Ans: a, b, e
Difficulty: 3
28. The genomes of humans and chimpanzees are about 99 percent similar yet many
evolutionary biologists believe that most of the apparent phenotypic differences between
the two species involve
a. several large chromosomal deletions
b. changes in regulatory DNA sequences
c. changes in DNA regulatory and developmental protein factors
d. transposition
e. minor chromosomal rearrangements
Ans: b, c, e
Difficulty: 4
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29. Silent (synonymous) nucleotide substitutions in codons involve the ___________
nucleotide position in the codon which is based on the ________________ hypothesis
involving codon and anticodon base pairing during translation.
a. 3'-third, Lyon
b. 3'-third, wobble
c. 5'-first, hydrogen bonding
d. 5'-first, wobble
e.
second, Ohno
Ans: b
Difficulty: 3
30. Mutations which result in the replacement of a serine amino acid with a glycine residue,
which are both hydrophobic amino acids, is considered a _________________________
amino acid substitution because the chance may have little effect on the normal function
of a particular protein.
a. synonymous
b. conservative
c. non-conservative
d. favorable
e. neutralized
Ans: b
Difficulty: 2
31. Nucleotide or amino acid substitutions that have no apparent effect on an organism's
phenotype, function, or development are considered _______________________
mutations.
a. neutral
b. conservative
c. advantageous
d. non-coding
e. reverse
Ans: a
Difficulty: 2
32. Human heterozygotes for sickle cell anemia are selectively more fit than the normal
homozygotes and considerably more fit than individuals homozygous for the sickle cell
allele. This enhanced fitness of the heterozygotes is known as:
a. adaptive value
b. reproductive fitness
c. heterozygous advantage
d. hybrid vigor
e. genetic drift
Ans: c
Difficulty: 2
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33. The beta globin gene superfamily has three major components located on three separate
chromosomes in humans, they are the beta globin gene family, the
______________________ gene family and the myoglobin gene.
a. alpha globin
b. Hba-ps4
c. gamma globin
d. delta globin
e. leghemoglobin
Ans: a
Difficulty: 2
34. In humans, the two functional adult alpha globin genes:
a. encode 8 different types of alpha globin chains.
b. encode proteins that form heterodimers in hemoglobin.
c. each have three very long introns.
d. encode identical polypeptide products.
e. are conserved by concerted evolution.
Ans: d, e
Difficulty: 4
35. The Hba-ps3 and Hba-ps4 pseudogenes which are located on mouse chromosomes 15
and 17 respectively are unlinked from the three principle globin gene families and thus
considered:
a. orphons.
b. transposable elements.
c. retrotransposons.
d. SINES.
e. LINES.
Ans: a
Difficulty: 2
36. Hox proteins have in common the functional capacity to:
a. transcribe target genes.
b. reduce gene expression in developmental genes.
c. function as DNA binding transcription factors.
d. transpose as a group.
e. function as epistatic regulators of 3' Hox genes.
Ans: c, e
Difficulty: 3
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37. The ancestral Hox gene family, which arose ________________ years ago, consisted of
_______ related genes that encode protein products that regulate the expression of other
genes.
a. 100 million, 8
b. 1 billion, 5
c. 65 million, 6
d. 600 million, 5
e. 100,000, 8
Ans: d
Difficulty: 3
38. LINE, SINE, and retroviral DNA sequences are considered by many evolutionary
biologists to be:
a. selfish DNA.
b. selectively neutral.
c. middle repetitive DNA sequences.
d. unique sequence DNA.
e. copied by the action of reverse transcriptase.
Ans: a, c, e
Difficulty: 2
39. SINE elements are evolutionarily related to:
a. signal recognition particle scRNA sequences.
b. tRNA sequences.
c. snRNP RNA species.
d. rRNA.
e. mRNA.
Ans: a, b
Difficulty: 4
40. LINE and SINE sequences evolve by the processes of episodic amplification and:
a. exon shuffling.
b. RNA splicing.
c. sequence degradation.
d. concerted evolution.
e. gene conversion.
Ans: c
Difficulty: 2
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41. Homologous LINE and SINE elements in close proximity on the same chromosome can
increase the rate of:
a. gene expression.
b. mutation.
c. unequal crossing over.
d. deletions.
e. duplications.
Ans: c, e
Difficulty: 3
42. Satellite DNA contains DNA sequence subsets that are useful for DNA fingerprinting
because of the inherent high level of polymorphisms that occur in their loci and include
which of the following components?
a. microsatellite sequences
b. minisatellite sequences
c. telomeric satellite sequences
d. centromeric satellite sequences
e. all of the above
Ans: e
Difficulty: 3
43. The human ________________ sequence is a noncoding 171 bp motif present in
tandem arrays in a 1 mb region of human centomeres.
a. deltoid
b. orphon
c. alphoid
d. microsatellite
e. pseudogene
Ans: c
Difficulty: 2
44. Telemeric repeated DNA sequences contain a hexomeric repeating unit containing a
_______________ sequence motif.
a. TTAGGG
b. GGGAAA
c. TTTAGG
d. TTTGGG
e. TGATGC
Ans: a
Difficulty: 2
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45. A 100 residue amino acid sequence called the ______________________________ is
common to all members of the immunoglobulin gene superfamily.
a. variable domain
b. constant domain
c. immunoglobulin homology unit
d. immunoglobulin binding site
e. beta-2 microglobulin domain
Ans: c
Difficulty: 2
46. The unique tertiary structure of the immunoglobulin fold permits it to:
a. resist proteolysis.
b. display a great diversity of recognition sites.
c. retains its three dimensional structure.
d. form trimeric molecules with other immunoglobulin folds.
e. none of the above.
Ans: a, b, c
Difficulty: 4
47. The immunoglobulin supergene family contains three different types of homology units
called variable (V), ___________________, and homology (H).
a. constant (C)
b. joining (J)
c. diversity (D)
d. CD4 (C)
e. CEA (C)
Ans: a
Difficulty: 2
48. The principle evolutionary mechanism that gave rise to the diverse immunoglobulin
supergene family was:
a. gene conversion.
b. exon shuffling.
c. genetic drift.
d. concerted evolution.
e. transposition.
Ans: b
Difficulty: 2
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49. The immunoglobulin gene families encode specific antigen receptor classes called:
a. T cell receptors.
b. antibodies.
c. beta-2 microglobulin.
d. MHC molecules.
e. a, b, and d above.
Ans: e
Difficulty: 2
50. Members of the immunoglobulin gene superfamily which carry out functions different
from vertebrate immune recognition include:
a. beta-2 microglobulin.
b. carcinoembryonic antigen.
c. contactin.
d. almagam.
e. MAG.
Ans: b, c, d, e
Difficulty: 3
51. Class I MHC molecules which are composed of a _____________________ chain and a
beta microglobulin chain, typically present __________________________ to T
cytotoxic cells.
a. light, pathogens
b. heavy, peptide fragments
c. light, native proteins
d. heavy, T-cell receptors
e. heavy, light chains
Ans: b
Difficulty: 3
52. An immune response has three basic components, it is highly specific, selects for
increased adaptivity, and:
a. has mutability.
b. has memory.
c. evolved rapidly by gene duplication.
d. is maintained by concerted evolution.
e. secretes antibody.
Ans: b
Difficulty: 2
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53. A diagram depicting evolutionary history of a gene is called a:
a. node.
b. branch diagram.
c. phylogenetic tree.
d. molecular clock.
Ans: c
Difficulty: 1
Matching
Match the following terms with the best definition
a. Kingdom
b. Hardy-Weinberg equilibrium
c. Burgess Shale
d. eukarya
e. Phylum
f. alpha helix
g. nucleus
h. First cellular life
i.
RNA secondary structure
j.
A,U,C,G
k. prokaryotes
l.
archaea
m. intramembrane system
n. punctuated equilibrium
o. North Pole, Australia
54. RNA alphabet
Ans: j
Difficulty: 1
55. complimentary base pairing in single stranded RNA molecules
Ans: i
Difficulty: 3
56. 3.5 billion years ago
Ans: h
Difficulty: 1
57. living representatives of the earliest life forms
Ans: l
Difficulty: 2
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58. compact genomes
Ans: k
Difficulty: 2
59. originated about 1.4 billion years ago
Ans: d
Difficulty: 1
60. the most universal feature of eukaryotic cells
Ans: m
Difficulty: 4
61. fossil evidence of the “explosion” of metazoan life forms
Ans: c
Difficulty: 2
62. taxonomic level based on “body plan”
Ans: e
Difficulty: 3
63. short bursts of rapid evolution
Ans: n
Difficulty: 2
Match the following terms with the best definition
a. C. Elegans
b. class I MHC genes
c. D. Melanogaster
d. M. Perutz
e. nodes
f. Gene superfamily
g. Multigene family
h. Simple sequence repeats
i.
branches
j.
Alu sequences
k. Tissue Plasminogen Activator
l.
fibronectin
m. human beta globin gene cluster
n. RRNA, tRNA, and histone genes
o. L. Pauling
64. examined hemoglobin and cytochrome c protein sequences
Ans: o
Difficulty: 1
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65. in phylogenetic trees, taxonomic unit are designated as
Ans: e
Difficulty: 2
66. (n)2, (n)3, (n)4, (n)5, etc.
Ans: h
Difficulty: 3
67. the first metazoan species whose complete genome has been sequenced
Ans: a
Difficulty: 2
68. 3'-locus control region
Ans: m
Difficulty: 3
69. Kringle, Growth Factor, and Finger
Ans: k
Difficulty: 3
70. A set of linked genes descended by duplication and divergence
Ans: g
Difficulty: 2
71. Arose by gene conversion from 38 donor pseudogenes to a small set of functional genes
Ans: b
Difficulty: 4
72. Conserved by one way gene conversion events within a species but can differ in
consensus sequence between different species
Ans: n
Difficulty: 3
73. Human globin genes
Ans: f
Difficulty: 2
True or False
74. Darwin was the first to propose that species could undergo evolution.
Ans: False
Difficulty: 2
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75. HIV genome has a high rate of mutation, about 1 in 50 nucleotides per replication.
Ans: False
Difficulty: 2
76. Ribozymes are RNA molecules that act as enzymes.
Ans: True
Difficulty: 1
77. Metazoans are multicellular animals.
Ans: True
Difficulty: 1
78. Punctuated equilibrium of evolution is the tendency of evolution to proceed through
long periods of stasis followed by short explosive periods of change.
Ans: True
Difficulty: 1
79. Humans diverged from chimpanzees about 6 billion years ago.
Ans: False
Difficulty: 2
80. Based on DNA genotyping, Neanderthal man was determined not to be a direct ancestor
of modern man.
Ans: True
Difficulty: 1
81. Species-specific differences in phenotype are most likely due to differences in gene
expression rather than mutations within genes.
Ans: True
Difficulty: 1
82. Nonsynonymous mutations have no effect on the amino acid encoded.
Ans: False
Difficulty: 2
83. There is evidence that synonymous mutations can be deleterious or favorable based on
availability of tRNA and their various synthetases.
Ans: True
Difficulty: 1
84. Most extremely rare mutations that have deleterious effects become fixed in a
population.
Ans: False
Difficulty: 2
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85. Duplications increase genome size and occur through transposition and unequal
crossing-over.
Ans: True
Difficulty: 1
86. Phylogenetic trees have nodes and branches; branches represent taxonomic units while
nodes represent the relationship of these units.
Ans: False
Difficulty: 2
87. Gene conversion outcome of unequal crossing-over allows the transfer of information
from one gene to another.
Ans: True
Difficulty: 1
88. Concerted evolution allows changes in single genetic elements to spread across a
complete set of genes in a gene family.
Ans: True
Difficulty: 1
Short Answer
89. Affinity maturation in which the immune response adaptively increases the fit between
antibody and antigen binding during B cell proliferation and differentiation is the result
of what underlying mechanism and how does it occur?
Ans: Somatic Hypermutation is responsible for causing 10 - 15 mutations in V region
immunoglobulin DNA sequences during the immune response in B-cells.
Mutations that increase the binding affinity of antibody to antigen will be
selectively amplified for clonal expansion.
Difficulty: 4
90. What are the five primary processes that account for the “generation of antibody
diversity?”
Ans: Germline diversity, Combinatorial joining, junctional diversity, somatic
hypermutation, and the joining of light and heavy immunoglobulin chains.
Difficulty: 3
91. What was the key evolutionary event in the evolution of the T-cell receptor gene family
and how might it have occurred?
Ans: The key events were the acquisition of the ability to rearrange DNA gene
segments via insertion of a transposable element into the 3' region of an ancestral
beta (T-cell receptor family) gene segment followed by gene duplication,
divergence, and adaptation.
Difficulty: 3
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92. What are the most interesting features of the human beta T-cell receptor family?
Ans: The 700 kb T-cell receptor gene family on chromosome 7 in humans contains 45
functional V beta gene segments, 19 pseudogene segments, 2 clusters containing 1
D segment and 5 - 6 functional J gene segments in 7 genomic modules, and LINE
and Alu repetitive sequence elements occupying about 36 percent of the total
DNA.
Difficulty: 4
93. What are three unique features of the Burgess Shale fossils?
Ans: The fossils have a great variety of basic “body plans,” the evolution of these
“body plans” occurred in a very short evolutionary time frame of about 10 - 20
million years, and all the phyla present today came into existence during this
Cambrian “explosion” of metazoan life forms.
Difficulty: 4
94. Catastrophic evolution has occurred a number of times during the evolution of life
forms on earth and has resulted in great changes in species numbers and dominance. If a
large asteroid struck the earth today what would be the effects of an oceanic impact and
what might be the consequences?
Ans: An asteroid impact into the sea would drastically alter earths climate and
ecosystem integrity for years following the event. Massive tidal waves, fires, acid
rain, and
atmospheric dust clouds would kill most organisms outright followed
by a great reduction in photosynthesis which would greatly impact both the
aquatic and terrestrial food chains. Mass extinctions would occur in the now
“toxic” environment heated by gasses and fires followed by deep cold. Could we
be among the species that are sufficiently adaptive or opportunistic to survive?
Difficulty: 4
95. Once life in cellular form emerged, living organisms evolved into three distinct domains
(kingdoms). What are they?
Ans: archaea, bacteria, and eukarya.
Difficulty: 2
96. In evolutionary terms, what is punctuated equilibrium?
Ans: The tendency of evolution to proceed through long periods of stasis (lack of
change) followed by short periods of considerable change.
Difficulty: 2
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Experimental Design and Interpretation of Data
97. What evolutionary conclusions can be drawn from a comparison of the human and
mouse beta T-cell receptor gene complexes?
Ans: DNA sequence analysis has revealed that very different repetitive DNA sequences
are spread throughout the region between both species. The general organization
of the genes has been evolutionarily conserved. Trypsinogen genes are associated
within the segments of both species but have been considerably more amplified in
the mouse while the human segments have experienced an enhanced amplification
of V beta T-cell genes.
Difficulty: 4
98. What three key requirements would be expected of a molecule capable of self
replication in the earliest proto cells?
Ans: The ancestral molecule may have been RNA which could have preceded DNA as
the repository of genetic information. The requirements for such a molecule in the
primordial RNA world would have to be: To encode genetic information in a
digital alphabet containing four RNA letters, assume variable three dimensional
structures capable of self replication and directing other cellular reactions, and to
expand the population of successful molecules and processes through selective
adaptation.
Difficulty: 4
99. Scientist have determined that chimpanzee and human genomes are approximately 99%
similar with nearly identical karyotypes yet remarkable differences exist in phenotypic
expression. Interpret this data.
Ans: The data suggests that developmental expression of genes leads to significant
differences between chimps and humans rather than absolute differences in
protein coding regions of the two genomes.
Difficulty: 3
100. Two hypothetical populations of animals exist, one is immense covering a large
continent and the other rather small which occupies an area the size of Chicago, IL.
Predict the effect of each population's size on its genetic drift.
Ans: The smaller the population, the more rapidly genetic drift effects it.
Difficulty: 3
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