Bio Chapter 17, 18, 19
Which of the following statements correctly describes the structure of chromatin?
Heterochromatin is highly condensed, whereas euchromatin is less compact.
How might a single base substitution in the sequence of a gene affect the amino acid sequence of a protein encoded by the gene?
Only a single amino acid could change, because the reading frame would be unaffected.
If individuals tend to mate within a subset of the population, there is ________.
random mating
What are telomeres?
the ends of linear chromosomes
The inability of organisms to evolve anything that could be an advantage reflects ________.
the limits of choices of genes within a species
Cell differentiation always involves
the production of tissue-specific proteins.
Gene expression is often assayed by measuring the level of mRNA produced from a gene. What level of the control of gene expression can by analyzed by this type of assay?
transcriptional control
In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of allele a is 0.2. What is the frequency of individuals that are heterozygous for this allele?
0.32
A fruit fly population has a gene with two alleles, A1 and A2. Tests show that 70% of the gametes produced in the population contain the A1 allele. If the population is in Hardy-Weinberg equilibrium, what proportion of the flies carry both A1 and A2?
0.42
You sample a population of butterflies and find that 56% are heterozygous at a particular locus. What should be the frequency of the homozygous individuals in this population?
0.50
In peas, a gene controls flower color such that R = purple and r = white. In an isolated pea patch, there are 36 purple-flowering plants and 64 white-flowering plants. Assuming Hardy-Weinberg equilibrium, what is the value of q for this population?
0.80
In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of allele a is 0.1. What is the frequency of individuals with AA genotype?
0.81
Which of the following mechanisms is used to coordinate the expression of multiple, related genes in eukaryotic cells?
A given gene may have multiple enhancers, but each enhancer is generally associated with only that gene and no other.
Who performed classic experiments that supported the semiconservative model of DNA replication?
Meselson and Stahl
In a nucleosome, the DNA is wrapped around
histones
In a nucleosome, the DNA is wrapped around
histones.
Within a cell, the amount of protein made using a given mRNA molecule depends partly on
the rate at which the mRNA is degraded.
A large population of laboratory animals has been allowed to breed randomly for a number of generations. After several generations, 25% of the animals display a recessive trait (aa), the same percentage as at the beginning of the breeding program. The rest of the animals show the dominant phenotype, with heterozygotes indistinguishable from the homozygous dominants. What proportion of the population is probably heterozygous (Aa) for this trait?
0.50
A particular triplet of bases in the template strand of DNA is 5′-AGT-3′. What would be the corresponding codon for the mRNA that is transcribed?
3′-UCA-5′
Arrange the following in order from most general to most specific. 1 natural selection 2. microevolution 3. intrasexual selection 4. evolution 5. sexual selection
4, 2, 1, 5, 3
Use the figure to answer the following question. Referring to the figure, what bases will be added to the primer as DNA replication proceeds?
5′ A, G, A, C, G, A, C 3′
In analyzing the number of different bases in a DNA sample, which result would be consistent with the base-pairing rules?
A + G = C + T
The genetic code is essentially the same for all organisms. From this, one can logically assume which of the following statements to be true?
A gene from an organism can theoretically be expressed by any other organism.
What would be the result of a mutation in a maternal effect gene in a female Drosophila?
All of her offspring will show the mutant phenotype, regardless of their genotype.
For a science fair project, two students decided to repeat the Hershey and Chase experiment, with modifications. They decided to radioactively label the nitrogen of the DNA, rather than the phosphate. They reasoned that each nucleotide has only one phosphate and two to five nitrogen atoms. Thus, labeling the nitrogen atoms would provide a stronger signal than labeling the phosphates. Why won't this experiment work?
Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins.
Use the figure to answer the following question. 4 test tubes, labeled: at the top, super 14 N DNA; in the middle super 14 N-super 15 N hybrid DNA; at the bottom super 15 N DNA. A, DNA helix at the bottom. B, DNA helices at top and bottom. C, helix at the top. D, helix in the center. A space probe returns with a culture of a microorganism found on a distant planet. Analysis shows that it is a carbon-based life-form that has DNA. You grow the cells in 15N medium for several generations and then transfer them to 14N medium. Which pattern in the figure would you expect if the DNA was replicated in a conservative manner?
B
Use the figure to answer the following question. 4 test tubes, labeled: at the top, super 14 N DNA; in the middle super 14 N-super 15 N hybrid DNA; at the bottom super 15 N DNA. A, DNA helix at the bottom. B, DNA helices at top and bottom. C, helix at the top. D, helix in the center. In the late 1950s, Meselson and Stahl grew bacteria in a medium containing "heavy" (radioactive) nitrogen (13N) and then transferred them to a medium containing 14N (non-radioactive). Which of the results in the figure would be expected after one round of DNA replication in the presence of 14N?
B
Which of the following effects might be caused by reduced or very little active telomerase activity?
Cells age and begin to lose function.
Codons are three-base sequences in mRNA that specify the addition of a single amino acid to the growing protein chain during translation. How do eukaryotic codons and prokaryotic codons compare?
Codons are a nearly universal language among all organisms.
Which of the following processes would allow the detection of alternative splicing of transcripts from a given gene?
Compare the sequences of different mRNAs made from the given gene.
Use the figure to answer the following question. 4 test tubes, labeled: at the top, super 14 N DNA; in the middle super 14 N-super 15 N hybrid DNA; at the bottom super 15 N DNA. A, DNA helix at the bottom. B, DNA helices at top and bottom. C, helix at the top. D, helix in the center. In the late 1950s, Meselson and Stahl grew bacteria in a medium containing "heavy" (radioactive) nitrogen (13N) and then transferred them to a medium containing 14N (non-radioactive). Which of the results in the figure would be expected after one round of DNA replication in the presence of 14N?
D
Hershey and Chase set out to determine what molecule served as the unit of inheritance. They completed a series of experiments in which E. coli was infected by a T2 virus. Which molecular component of the T2 virus actually ended up inside the cell?
DNA
Suppose you are provided with an actively dividing culture of E. coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates once in the presence of this radioactive base?
DNA in both daughter cells would be radioactive.
A biochemist isolates, purifies, and combines in a test tube a variety of molecules needed for DNA replication. When she adds some DNA to the mixture, replication occurs, but each DNA molecule consists of a normal strand paired with numerous segments of DNA a few hundred nucleotides long. What has she probably left out of the mixture?
DNA ligase
Why does a new DNA strand elongate only in the 5' to 3' direction during DNA replication?
DNA polymerase can add nucleotides only to the free 3' end.
What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized?
DNA polymerase can join new nucleotides only to the 3′ end of a pre-existing strand, and the strands are antiparallel.
Which statement about the beak size of finches on the island of Daphne Major during prolonged drought is true?
Each bird's survival was strongly influenced by the depth and strength of its beak as the drought persisted.
Which of the following statements accurately describes one characteristic of histones?
Histone H1 is not present in the nucleosome bead; instead, it draws the nucleosomes together.
Which of the following molecular characteristics cause histones to bind tightly to DNA?
Histones are positively charged, and DNA is negatively charged.
Which of the following structural characteristics is most critical for the association between histones and DNA?
Histones are positively charged.
Which of the following statements correctly describes the effect a nonsense mutation would have on a gene?
It introduces a premature stop codon into the mRNA.
In his transformation experiments, what phenomenon did Griffith observe?
Mixing a heat-killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form.
In 1986, a nuclear power accident in Chernobyl, USSR (now Ukraine), led to high radiation levels for miles surrounding the plant. The high levels of radiation caused elevated mutation rates in the surviving organisms, and evolutionary biologists have been studying rodent populations in the Chernobyl area ever since. Based on your understanding of evolutionary mechanisms, which of the following most likely occurred in the rodent populations following the accident?
Mutation led to increased genetic variation.
In E. coli, there is a mutation in a gene called dnaB that alters the helicase that normally acts at the origin of replication. Which of the following events would you expect to occur as a result of this mutation?
No replication fork will be formed.
In a healthy eukaryotic cell, the rate of DNA repair is typically equal to the rate of DNA mutation. When the rate of repair lags behind the rate of mutation, what is a possible fate of the cell?
The cell can be transformed into a cancerous cell.
Which of the following statements correctly describes the difference between ATP and the nucleotides used during DNA synthesis?
The nucleotides have the sugar deoxyribose; ATP has the sugar ribose.
Which of the following processes do normal proto-oncogenes typically exhibit?
They stimulate normal cell growth and division.
Which of the following statements is true about protein synthesis in prokaryotes?
Translation can begin while transcription is still in progress.
In 1983, a population of dark-eyed junco birds became established on the campus of the University of California, San Diego (UCSD), which is located many miles from the junco's normal habitat in the mixed-coniferous temperate forests in the mountains. Juncos have white outer tail feathers that the males display during aggressive interactions and during courtship displays. Males with more white in their tail are more likely to win aggressive interactions, and females prefer to mate with males with more white in their tails. Females have less white in their tails than do males, and display it less often. (Pamela J. Yeh. 2004. Rapid evolution of a sexually selected trait following population establishment in a novel habitat. Evolution 58[1]:166-74.) The UCSD campus male junco population tails were, on average, 36% white, whereas the tails of males from nearby mountain populations averaged 40-45% white. If this observed trait difference were due to a difference in the original colonizing population, it would most likely be due to ________. a founder effect
a founder effect
Which of the following types of mutation would convert a proto-oncogene into an oncogene?
a mutation that greatly increases the amount of the proto-oncogene protein
Which of the following characteristics would you expect of a eukaryotic organism that lacks the enzyme telomerase?
a reduction in chromosome length in gametes
A researcher introduces double-stranded RNA into a culture of mammalian cells and can identify its location or that of its smaller subsections experimentally, using a fluorescent probe. Some time later, she finds that the introduced strand separates into single-stranded RNAs, one of which is degraded. What does this enable the remaining strand to do?
bind to complementary regions of target mRNAs
How do steroid hormones produce their effects in cells?
by binding to intracellular receptors and promoting transcription of specific genes
How does extracellular glucose inhibit transcription of the lac operon?
by reducing the levels of intracellular cAMP
Microevolutions occur when ________.
changes in allele frequencies in a population occur over generations
Which of the following is the most predictable outcome of increased gene flow between two populations?
decreased genetic difference between the two populations
Three-spined stickleback fish (Gasterosteus aculeatus) show substantial heritable variation in gill-raker length related to differences in their diets. Longer gill rakers appear to function better for capturing open-water prey, while shorter gill rakers function better for capturing shallow-water prey. Which of the following types of selection is most likely to be found in a large lake (open water in the middle and shallow water around the sides) with a high density of these fish?
disruptive selection
Which of the following are maternal effect genes that control the orientation of the egg and thus the Drosophila embryo?
egg-polarity genes
DNA methylation and histone acetylation are examples of which of the following processes?
epigenetic phenomena
Cystic fibrosis is a genetic disorder in homozygous recessives that causes death during the teenage years. If 9 in 10,000 newborn babies have the disease, what are the expected frequencies of the dominant (A1) and recessive (A2) alleles according to the Hardy-Weinberg equation?
f(A1) = 0.9700, f(A2) = 0.0300
Over time, the movement of people on Earth has steadily increased. This has altered the course of human evolution by increasing ________.
gene flow
Which Hardy-Weinberg condition is affected by population size?
genetic drift
There are 25 individuals in population 1, all with genotype AA, and there are 40 individuals in population 2, all with genotype aa. Assume that these populations are located far from each other and that their environmental conditions are very similar. Based on the information given here, the observed genetic variation most likely resulted from
genetic drift.
In the formula for determining a population's genotype frequencies, the "2" in the term 2pq is necessary because ________.
heterozygotes can come about in two ways
Homozygotes with two sickle-cell alleles are selected against because of mortality. However, heterozygotes for sickle-cell allele experience little effects of sickle allele and are more likely to survive malaria. The net effect of this exposure produced evolutionary change in areas where malaria is endemic by ________.
increasing sickle-cell allele frequency
How are bacteria able to change their patterns of protein synthesis so quickly in response to environmental changes?
mRNAs that are produced are short-lived and degraded within a few minutes of being synthesized.
A proficient engineer can easily design skeletal structures that are more functional than those currently found in the forelimbs of such diverse mammals as horses, whales, and bats. The actual forelimbs of these mammals do not seem to be optimally arranged because ________.
natural selection is generally limited to modifying structures that were present in previous generations and in previous species
Which of the following lists represents the order of increasingly higher levels of organization of chromatin?
nucleosome, 30-nm chromatin fiber, looped domain
The higher the proportion of loci that are "fixed" in a population, the lower are that population's ________.
nucleotide variability and average heterozygosity
E. coli cells grown on 15N medium are transferred to 14N medium and allowed to grow for two more generations (two rounds of DNA replication). DNA extracted from these cells is centrifuged. What density distribution of DNA would you expect in this experiment?
one low-density and one intermediate-density band
Semiconservative replication involves a template. What is the template?
one strand of the DNA molecule
Which of the following types of cells are affected most by telomere shortening?
only eukaryotic cells
A heat-killed, phosphorescent (light-emitting) strain of bacteria is mixed with a living, non-phosphorescent strain. Further observations of the mixture show that some of the living cells are now phosphorescent. Which of the following observations would provide the best evidence that the ability to phosphoresce is a heritable trait?
phosphorescence in descendants of the living cells
Which of the following molecules is a protein produced by a regulatory gene?
repressor
It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information. Which of the following characteristics of DNA is responsible for this?
sequence of bases
The reason for differences in the sets of proteins expressed in a nerve and a pancreatic cell of the same individual is that nerve and pancreatic cells contain different ________.
sets of regulatory proteins
Which one of the following conditions would allow gene frequencies to change by chance?
small populations
In his work with pneumonia-causing bacteria and mice, Griffith found that
some substance from pathogenic cells was transferred to nonpathogenic cells, making them pathogenic.
Most Swiss starlings produce four to five eggs in each clutch. Starlings producing fewer or more than this have reduced fitness. Which of the following terms best describes this situation?
stabilizing selection
Whenever diploid populations are in Hardy-Weinberg equilibrium at a particular locus, ________.
the allele's frequency should not change from one generation to the next
Which of the following is an example of post-transcriptional control of gene expression?
the removal of introns and alternative splicing of exons
No two people are genetically identical, except for identical twins. The main source of genetic variation among humans is
the reshuffling of alleles in sexual reproduction.
Which of the following processes is the first event to take place in translation in eukaryotes?
the small subunit of the ribosome recognizes and attaches to the 5′ cap of mRNA
In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of the allele a is 0.3. What is the frequency of individuals that are homozygous for this allele?
0.09
In some jacana species, males take care of the eggs and young, and females compete among themselves for territories that contain one to several males. Female jacanas are significantly larger than males. Which of these statements would you predict to be true of this bird species? 1. Male jacana fitness is primarily limited by ability to take care of eggs and raise young. 2. Female jacana fitness is limited by the number of males in her territory with which a female mates. 3. Variation in reproductive success should be greater in male jacanas than in females. 4. Variation in reproductive success should be greater in female jacanas than in males. 5. Males and females have equal variation in reproductive success.
1, 2, and 4
Use the figure to answer the question. An arrow labeled enzyme A points from A to B; a similar arrow labeled enzyme B points from B to C. The figure shows a simple metabolic pathway. According to Beadle and Tatum's hypothesis, how many genes are necessary for this pathway?
2
Thymine makes up 28% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be guanine?
22
Thymine makes up 28% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be guanine?
22%
Use the figure to answer the question. An arrow labeled enzyme A points from A to B; a similar arrow labeled enzyme B points from B to C. The figure shows a simple metabolic pathway. According to Beadle and Tatum's hypothesis, how many genes are necessary for this pathway?
3
Suppose 64% of a remote mountain village can taste phenylthiocarbamide (PTC) and must, therefore, have at least one copy of the dominant PTC taster allele. If this population conforms to Hardy-Weinberg equilibrium for this gene, what percentage of the population must be heterozygous for this trait?
48%
At a specific area of a chromosome, the sequence of nucleotides below is present where the chain opens to form a replication fork: 3' C C T A G G C T G C A A T C C 5' An RNA primer is formed starting at the underlined T (T) of the template. Which of the following represents the primer sequence?
5' A C G U U A G G 3'
Cytosine makes up 42% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine?
8%
Which statement about variation is true?
All new alleles are the result of nucleotide variability.
Why does the fitness of a phenotype depend on frequency-dependent selection?
Because frequency-dependent selection acts against extreme phenotypes.
DNA contains the template needed to copy itself, but it has no catalytic activity in cells. What catalyzes the formation of phosphodiester bonds between adjacent nucleotides in the DNA polymer being formed during DNA replication?
DNA polymerase
In E. coli, which enzyme catalyzes the elongation of a new DNA strand in the 5' → 3' direction?
DNA polymerase III
The lagging strand is characterized by a series of short segments of DNA (Okazaki fragments) that will be joined together to form a finished lagging strand. The experiments that led to the discovery of Okazaki fragments gave evidence for which of the following ideas?
DNA polymerase is an enzyme that synthesizes leading and lagging strands during replication only in one direction.
In DNA replication, the resulting daughter molecules contain one strand of the original parental DNA and one new strand. What is the explanation for this phenomenon?
DNA replication is semiconservative.
The following experiment is used for the corresponding question. A researcher discovered a species of moth that lays its eggs on oak trees. Eggs are laid at two distinct times of the year: early in spring when the oak trees are flowering and in midsummer when flowering is past. Caterpillars from eggs that hatch in spring feed on oak flowers and look like oak flowers. But caterpillars that hatch in summer feed on oak leaves and look like oak twigs. How does the same population of moths produce such different-looking caterpillars on the same trees? To answer this question, the biologist caught many female moths from the same population and collected their eggs. He put at least one egg from each female into eight identical cups. The eggs hatched, and at least two larvae from each female were maintained in one of the four temperature and light conditions listed below. Four conditions of temperature and day length: Both springlike; springlike temperature and summerlike day length; summerlike temperature and springlike day length; both summerlike. In each of the four environments, one of the caterpillars was fed oak flowers, the other oak leaves. Thus, there were a total of eight treatment groups (4 environments × 2 diets). Which of the following is a testable hypothesis that would explain the differences in caterpillar appearance observed in this population?
Differences in diet trigger the development of different types of caterpillars.
Which of the following investigators was (were) responsible for the discovery that in DNA from any species, the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine?
Erwin Chargaff
Which of the following statements describes the process of transformation in bacteria?
External DNA is taken into a cell, becoming part of the cell's genome.
Swine are vulnerable to infection by bird flu virus and human flu virus, which can both be present in an individual pig at the same time. When this occurs, it is possible for genes from bird flu virus and human flu virus to be combined. If the human flu virus contributes a gene for Tamiflu resistance (Tamiflu is an antiviral drug) to the new virus, and if the new virus is introduced to an environment lacking Tamiflu, then what is most likely to occur?
If the Tamiflu-resistance gene involves a cost, it will experience directional selection leading to reduction in its frequency.
How does the enzyme telomerase meet the challenge of replicating the ends of linear chromosomes?
It catalyzes the lengthening of telomeres, compensating for the shortening that could occur during replication without telomerase activity.
Which of the following statements correctly describes the function of a signal peptide?
It helps target a protein to the ER.
Which of the following statements accurately describes the structure of a eukaryotic chromosome?
It is a single linear molecule of double-stranded DNA plus proteins.
What is the role of DNA ligase in the elongation of the lagging strand during DNA replication?
It joins Okazaki fragments together.
Within a double-stranded DNA molecule, adenine forms hydrogen bonds with thymine, and cytosine forms hydrogen bonds with guanine. What is the significance of the structural arrangement?
It permits complementary base pairing.
Which of the following properties is associated with a protein that will be secreted from a eukaryotic cell?
Its signal sequence must target it to the ER, after which it goes to the Golgi.
The restriction enzymes of bacteria protect the bacteria from successful attack by bacteriophages, whose genomes can be degraded by the restriction enzymes. The bacterial genomes are not vulnerable to these restriction enzymes because bacterial DNA is methylated. This situation selects for bacteriophages whose genomes are also methylated. As new strains of resistant bacteriophages become more prevalent, this in turn selects for bacteria whose genomes are not methylated and whose restriction enzymes instead degrade methylated DNA. Over the course of evolutionary time, what should occur?
Methylated and nonmethylated strains should be maintained among both bacteria and bacteriophages, with ratios that vary over time.
Use the following information to answer the question below. Researchers studying a small milkweed population note that some plants produce a toxin and other plants do not. They identify the gene responsible for toxin production. The dominant allele (T) codes for an enzyme that makes the toxin, and the recessive allele (t) codes for a nonfunctional enzyme that cannot produce the toxin. Heterozygotes produce an intermediate amount of toxin. The genotypes of all individuals in the population are determined (see chart) and used to determine the actual allele frequencies in the population. Genotype frequencies are TT, 0.56; Tt, 0.28; tt 0.16. Allele frequencies have two boxes each labeled T with no frequency shown. Is this population in Hardy-Weinberg equilibrium?
No; there are more homozygotes than expected.
Which of the following statements accurately describes the differences between DNA replication in prokaryotes and DNA replication in eukaryotes?
Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have many.
Which of the following statements best describes the termination of transcription in prokaryotes?
RNA polymerase transcribes through the terminator sequence, causing the polymerase to separate from the DNA and release the transcript.
After the first replication was observed in their experiments testing the nature of DNA replication, Meselson and Stahl could be confident of which of the following conclusions?
Replication is not conservative.
In DNA replication in E. coli, the enzyme primase is used to attach a 5 to 10 base ribonucleotide strand complementary to the parental DNA strand. The RNA strand serves as a starting point for the DNA polymerase that replicates the DNA. If a mutation occurred in the primase gene, which of the following results would you expect?
Replication would not occur on either the leading or lagging strand.
Telomere shortening puts a limit on the number of times a cell can divide. Research has shown that telomerase can extend the life span of cultured human cells. How might adding telomerase affect cellular aging?
Telomerase eliminates telomere shortening and retards aging.
What is meant by the description "antiparallel" regarding the two strands that make up the DNA double helix?
The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand.
Which of the following statements describes a cell that is considered to be differentiated?
The cell produces proteins specific to a particular cell type.
If a cell were unable to produce histone proteins, which of the following results would be a likely effect on the cell?
The cell's DNA could not be packed into its nucleus.
Which of the following conditions is most likely to cause the lactose operon to be transcribed?
The cyclic AMP and lactose levels are both high within the cell.
Individuals with the disorder xeroderma pigmentosum are hypersensitive to sunlight, and mutations to the DNA in their skin cells are left uncorrected. Why are the mutations not corrected in individuals with this disorder?
The disorder causes cells to be unable to repair thymine dimers.
Suppose an experimenter becomes proficient with a technique that allows her to move DNA sequences within a prokaryotic genome. If a researcher moves the operator to the far end of the operon, past the transacetylase (lacA) gene, which of the following processes would likely occur when the cell is exposed to lactose?
The genes of the lac operon will be transcribed continuously.
Suppose an experimenter becomes proficient with a technique that allows her to move DNA sequences within a prokaryotic genome. If a researcher moves the repressor gene (lacI), along with its promoter, to a position at some several thousand base pairs away from its normal position, which of the following results would be expected?
The lac operon will function normally.
According to the lac operon model proposed by Jacob and Monod, what is predicted to occur if the operator is removed from the operon?
The lac operon would be transcribed continuously.
Which of the following statements correctly describes the difference between the leading strand and the lagging strand in DNA replication?
The leading strand is synthesized continuously in the 5' → 3' direction, while the lagging strand is synthesized discontinuously in the 5' → 3' direction.
Which of the following statements correctly describes the difference between the leading and the lagging strands of DNA during DNA replication?
The leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction.
Researchers found a strain of E. coli bacteria that had mutation rates one hundred times higher than normal. Which of the following statements correctly describes the most likely cause of these results?
The proofreading mechanism of DNA polymerase was not working properly.
A large population of laboratory animals has been allowed to breed randomly for a number of generations. After several generations, 25% of the animals display a recessive trait (aa), the same percentage as at the beginning of the breeding program. The rest of the animals show the dominant phenotype, with heterozygotes indistinguishable from the homozygous dominants. What is the most reasonable conclusion that can be drawn from the fact that the frequency of the recessive trait (aa) has not changed over time?
The two phenotypes are about equally adaptive under laboratory conditions.
HIV's genome of RNA includes the code for reverse transcriptase (RT), an enzyme that acts early in infection to synthesize a DNA genome off of an RNA template. The HIV genome also codes for protease (PR), an enzyme that acts later in infection by cutting long viral polyproteins into smaller, functional proteins. Both RT and PR represent potential targets for antiretroviral drugs. Drugs called nucleoside analogs (NA) act against RT, whereas drugs called protease inhibitors (PI) act against PR. Which of the following treatment options would most likely avoid the evolution of drug-resistant HIV (assuming no drug interactions or side effects)?
Use moderate doses of NA and two different PIs at the same time for several months.
Which of the following types of cells are affected most by telomere shortening?
Which of the following types of cells are affected most by telomere shortening?
Hershey and Chase used a DNA-based virus for their work. How might the results have been different if they had used an RNA virus?
With an RNA virus, radioactive RNA would have been in the final pellet.
A single base substitution mutation is likely to have a less deleterious effect when the base change exhibits which of the following results?
a codon that specifies the same amino acid as the original codon
An earthquake decimates a ground-squirrel population, killing 98% of the squirrels. The surviving population happens to have broader stripes, on average, than the initial population. If broadness of stripes is genetically determined, what effect has the ground-squirrel population experienced during the earthquake?
a genetic bottleneck
Altering patterns of gene expression in prokaryotes would most likely serve an organism's survival by ________.
allowing an organism to adjust to changes in environmental conditions
Which of the following methods is utilized by eukaryotes to control their gene expression that is different from the type of control found in bacteria?
control of both RNA splicing and chromatin remodeling
You are maintaining a small population of fruit flies in the laboratory by transferring the flies to a new culture bottle after each generation. After several generations, you notice that the viability of the flies has decreased greatly. Recognizing that small population size is likely to be linked to decreased viability, the best way to reverse this trend is to ________.
cross your flies with flies from another lab
A researcher found a method she could use to manipulate and quantify phosphorylation and methylation in embryonic cells in culture. In one set of experiments, she succeeded in increasing acetylation of histone tails in the chromatin of the cells. Which of the following results would she most likely see in these cells?
decreased chromatin condensation
The elongation of the leading strand during DNA synthesis
depends on the action of DNA polymerase.
Which of the following is the best modern definition of evolution?
descent with modification
Which of the following descriptions illustrates phenotype variation caused by environment?
diet of caterpillars changes their morphology
The fact that plants can be cloned from somatic cells demonstrates that ________.
differentiated cells retain all the genes of the zygote
XY axis, with X showing Measured Variation in Trait and Y showing number of individuals. Line approximates a bell curve, rising from 0,0 and returning to 0 farther along the x axis In a very large population, a quantitative trait has the following distribution pattern. If there is no gene flow, the curve shifts to the left or to the right, and the population size consequently increases over successive generations, which of the following is most likely occurring? directional selection
directional selection
A biologist doing a long-term study on a wild spider population observes increased variation in silk thickness. Which of the following could the spider population be experiencing?
disruptive selection
The Dunkers are a religious group that moved from Germany to Pennsylvania in the mid-1700s. They do not marry with members outside their own immediate community. Today, the Dunkers are genetically unique and differ in gene frequencies, at many loci, from all other populations including those in their original homeland. Which of the following mechanisms likely explains the genetic uniqueness of this population?
founder effect and genetic drift
When imbalances occur in the sex ratio of sexual species that have two sexes (that is, other than a 50:50 ratio), the members of the minority sex often receive a greater proportion of care and resources from parents than do the offspring of the majority sex. This is most clearly an example of ________.
frequency-dependent selection
Which of the following characteristics of eukaryotic telomeres cause them to replicate differently than the rest of the chromosome?
gaps left at the 5' end of the lagging strand template
Comparisons of Neanderthal DNA revealed that there are more similarities to non-African DNA than reference sequences from West Africans. Additionally, scientists found that Neanderthal DNA is as closely related to East Asians as to Europeans. This indicates that interbreeding occurred before human migration further east. What process of population genetics generated these results?
gene flow
Natural selection changes allele frequencies because some ________ survive and reproduce better than others.
individuals
Most repressor proteins are allosteric. Which of the following molecules binds with the repressor to alter its conformation and therefore affect its function?
inducer
When taken up by a cell, which of the following molecules binds to a repressor so that the repressor no longer binds to the operator?
inducer
You briefly expose bacteria undergoing DNA replication to radioactively labeled nucleotides. When you centrifuge the DNA isolated from the bacteria, the DNA separates into two classes. One class of labeled DNA includes very large molecules (thousands or even millions of nucleotides long), and the other includes short stretches of DNA (several hundred to a few thousand nucleotides in length). Which two classes of DNA do these different samples represent?
leading strands and Okazaki fragments
On the Bahamian island of Andros, mosquitofish populations live in various, now-isolated, freshwater ponds that were once united. Currently, some predator-rich ponds have mosquitofish that can swim in short, fast bursts; other predator-poor ponds have mosquitofish that can swim continuously for a long time. When placed together in the same body of water, the two kinds of female mosquitofish exhibit exclusive breeding preferences. If one builds a canal linking a predator-rich pond to a predator-poor pond, then what type of selection should subsequently be most expected among the mosquitofish in the original predator-rich pond, and what type should be most expected among the mosquitofish in the formerly predator-poor pond?
less-intense directional selection; more-intense directional selection
Genetic variation ________.
must be present in a population before natural selection can act upon the population
In E. coli, to repair a thymine dimer by nucleotide excision repair, in which order do the necessary enzymes act?
nuclease, DNA polymerase, DNA ligase
The spontaneous loss of amino groups from adenine in DNA results in hypoxanthine, an uncommon base, opposite thymine. What combination of proteins could repair such damage?
nuclease, DNA polymerase, DNA ligase
Among the newly discovered small noncoding RNAs, one type helps to reestablish ethylation patterns during gamete formation and blocks expression of some transposons. Which of the following types of RNA is responsible for this function?
piRNA
What is the function of the enzyme topoisomerase in DNA replication?
relieving strain in the DNA ahead of the replication fork caused by the untwisting of the double helix
Adult male humans generally have deeper voices than do adult female humans, which is the direct result of higher levels of testosterone causing growth of the larynx. If the fossil records of apes and humans alike show a trend toward decreasing larynx size in adult females and increasing larynx size in adult males, then ________.
sexual dimorphism was evolving over time in these species
Which of the following types of molecules help to hold the DNA strands apart while they are being replicated?
single-strand DNA binding proteins
Use the following information to answer the question below. Martin Wikelski and L. Michael Romero (Body size, performance and fitness in Galápagos marine iguanas, Integrative and Comparative Biology 43 [2003]:376-86) measured the snout-to-vent (anus) length of Galápagos marine iguanas and observed the percent survival of different-sized animals, all of the same age. The graph shows the log snout-vent length (SVL, a measure of overall body size) plotted against the percent survival of these different size classes for males and females. Line graph: x is Log SVL in mm; y is survival percent. Solid line starts at 2.1 SVL, 50%, rises to almost 100% at SVL 2.4, then declines. Dotted starts at 2.2 SVL, rises to above 90% at 2.3, stays steady, then declines to end at 2.5 SVL, 75% Examine the figure. What type of selection for body size appears to be occurring in these marine iguanas?
stabilizing selection
Which one of these processes describes bottleneck effect?
sudden change in environments that alters gene frequency of a population
In the polymerization of DNA, a phosphodiester bond is formed between a phosphate group of the nucleotide being added and which of the following atoms or molecules of the last nucleotide in the polymer?
the 3' OH
Map of Hawaii showing islands from northwest to southeast, and for some a time frame: Kauai, 5.1 million years; Oahu, 3.7 million years; Molokai; Lanai; Maui, 1.3 million years; Hawaii, 0.4 million years. Soon after the island of Hawaii rose above the sea surface (somewhat less than one million years ago), the evolution of life on this new island should have been most strongly influenced by ________.
the founder effect
Which of the following characteristics is directly related to the coding of a single amino acid during the process of translation?
the three-base sequence of mRNA
In E. coli, what is the function of DNA polymerase III?
to add nucleotides to the 3' end of a growing DNA strand
The functioning of enhancers is an example of
transcriptional control of gene expression.