Explanation of this is

a. normal mitosis.

b. normal meiosis.

c. nondisjunction in meiosis I.

d. nondisjunction in meiosis I and II.

e. nondisjunction in mitosis.

10. The number of daughter chromosomes in a human cell in anaphase II of meiosis is

a. 2.

b. 23.

c. 46.

d. 69.

e. 92.

Test questions 5

1. In a simple Mendelian monohybrid cross, tall plants were crossed with short plants and the F1 were crossed among themselves. What fraction of the F2 generation are both tall and heterozygous?

a. 1 ⁄8

b. 1⁄4

c. 1⁄3

d. 2⁄3

e. 1⁄2

2. The phenotype of an individual

a. depends at least in part on the genotype.

b. is either homozygous or heterozygous.

c. determines the genotype.

d. is the genetic constitution of the organism.

e. is either monohybrid or dihybrid.

3. The ABO blood groups in humans are determined by a multiple allelic system where IA and IB are codominant and dominant to IO. A newborn infant is type A. The mother is type O. Possible genotypes of the father are:

a. A, B or AB

b. A, B or O

c. O only

d. A or AB

e. A or O

4. Which statement about an individual that is homozygous for an allele is not true?

a. Each of its cells possesses two copies of that allele.

b. Each of its gametes contains one copy of that allele.

c. It is true-breeding with respect to that allele.

d. Its parents were necessarily homozygous for that allele.

e. It can pass that allele to its offspring.

5. Which statement about a test cross is not true?

a. It tests whether an unknown individual is homozygous or heterozygous.

b. The test individual is crossed with a homozygous recessive individual.

c. If the test individual is heterozygous, the progeny will have a 1:1 ratio.

d. If the test individual is homozygous, the progeny will have a 3:1 ratio.

e. Test cross results are consistent with Mendel’s model of inheritance.

6. Linked genes

a. must be immediately adjacent to one another on a chromosome.

b. have alleles that assort independently of one another.

c. never show crossing over.

d. are on the same chromosome.

e. always have multiple alleles.

7. In the F2 generation of a dihybrid cross

a. 4 phenotypes appear in the ratio 9:3:3:1 if the loci are linked.

b. 4 phenotypes appear in the ratio 9:3:3:1 if the loci are unlinked.

c. 2 phenotypes appear in the ratio 3:1 if the loci are unlinked.

d. 3 phenotypes appear in the ratio 1:2:1 if the loci are unlinked.

e. 2 phenotypes appear in the ratio 1:1 whether or not the loci are linked.

8. The sex of a human is determined by

a. ploidy, the male being haploid.

b. the Y chromosome.

c. X and Y chromosomes, the male being XY.

d. the number of X chromosomes, the male being XO.

e. Z and W chromosomes, the male being ZZ.

9. In epistasis

a. nothing changes from generation to generation.

b. one gene alters the effect of another.

c. a portion of a chromosome is deleted.

d. a portion of a chromosome is inverted.

e. the behavior of two genes is entirely independent.

10. In humans, spotted teeth is caused by a dominant sexlinked gene. A man with spotted teeth whose mother had normal teeth marries a woman with normal teeth. Therefore,a. all of their daughters will have normal teeth.

b. all of their daughters will have spotted teeth.

c. all of their children will have spotted teeth.

d. half of their sons will have spotted teeth.

e. none of their sons will have spotted teeth.

Test questions 6

1. Which of the following is not a difference between RNA andDNA?

a. RNA has uracil; DNA has thymine.

b. RNA has ribose; DNA has deoxyribose.

c. RNA has five bases; DNA has four.

d. RNA is a single polynucleotide strand; DNA is a double

strand.

e. RNA is relatively smaller than human chromosomal DNA.

2. Normally, Neurospora can synthesize all 20 amino acids. A certain strain of this mold cannot grow in simple growth medium but grows only when the amino acid leucine is added to the medium. This strain is

a. dependent on leucine for energy.

b. mutated in the synthesis of all proteins.

c. mutated in the synthesis of all 20 amino acids

d. mutated in the synthesis of leucine.

e. mutated in the syntheses of 19 of the 20 amino acids.

3. An mRNA has the sequence 5′-AUGAAAUCCUAG-3′. What is the template DNA strand for this sequence?

a. 5′-TACTTTAGGATC-3′

b. 5′-ATGAAATCCTAG-3′

c. 5′-GATCCTAAAGTA-3′

d. 5′-TACAAATCCTAG-3′

e. 5′-CTAGGATTTCAT-3′

4. The adapters that allow translation of the four-letter nucleic acid language into the 20 letter protein language are called

a.aminoacyl tRNA synthetases.

b. transfer RNAs.

c. ribosomal RNAs.

d. messenger RNAs.

e. ribosomes.

5. At a certain location in a gene, the nontemplate strand of DNA has the sequence GAA. Amutation alters the triplet to GAG. This type of mutation is called

a. silent.

b. missense.

c. nonsense.

d. frame-shift.

e. translocation.

6. Transcription

a. produces only mRNA.

b. requires ribosomes.

c. requires tRNAs.

d. produces RNA growing from the 5′end to the 3′end.

e. takes place only in eukaryotes.

7. Which statement about translation is not true?

a. It is RNA-directed polypeptide synthesis.

b. An mRNA molecule can be translated by only one ribosome at a time.

c. The same genetic code operates in almost all organisms and organelles.

d. Any ribosome can be used in the translation of any mRNA.

e. There are both start and stop codons.

8. Which statement is not true?

a. Transfer RNA functions in translation.

b. Ribosomal RNA functions in translation.

c. RNAs are produced in transcription.

d. Messenger RNAs are produced on ribosomes.

e. DNA codes for mRNA, tRNA, and rRNA.

9. The genetic code

a. is different for prokaryotes and eukaryotes.

b. has changed during the course of recent evolution.

c. has 64 codons that code for amino acids.

d. is degenerate.

e. is ambiguous.

10. A mutation that results in the codon UAG where there had been UGG is

a. a nonsense mutation.

b. a missense mutation.

c. a frame-shift mutation.

d. a large-scale mutation.

e. unlikely to have a significant effect.

Test questions 7

1. The two major components of Darwin’s theory of evolutionare that

a. evolution is a fact and mutations are the agent of evolution.

b. evolution is a fact and natural selection is the agent of evolution.

c. species cannot change into other species, but natural

selection can modify them.

d. species cannot change into other species but mutations

can modify them.

e. evolution is a hypothesis, and genetic drift is the agent of

evolution.

2. To ground his theory, Charles Darwin

a. developed a comprehensive theory of inheritance.

b. described several evolutionary changes and identified the

agents that caused them.

c. used patterns of domestication to show how his theory

differed from those patterns.

d. assembled a broad base of supporting information from

many fields.

e. developed a mathematical model of evolutionary change.

3. The phenotype of an organism is

a. the type specimen of its species in a museum.

b. its genetic constitution, which governs its traits.

c. the chronological expression of its genes.

d. the physical expression of its genotype.

e. the form it achieves as an adult.

4. The appropriate unit for defining and measuring geneticvariation is the

a. cell.

b. individual.

c. population.

d. community.

e. ecosystem.

5. Which statement about allele frequencies is not true?

a. The sum of any set of allele frequencies is always 1.

b. If there are two alleles at a locus and we know the frequency

of one of them, we can obtain the frequency of

the other by subtraction.

c. If an allele is missing from a population, its frequency is 0.

d. If two populations have the same gene pool for a locus, they will have the same proportion of homozygotes at that locus.

e. If there is only one allele at a locus, its frequency is 1.

6. In a population at Hardy–Weinberg equilibrium in which the frequency of A alleles (p) is 0.3, the expected frequency of Aa individuals is

a. 0.21.

b. 0.42.

c. 0.63.

d. 0.18.

e. 0.36.

7. Natural selection that preserves existing allele frequencies is called

a. unidirectional selection.

b. bidirectional selection.

c. prevalent selection.

d. stabilizing selection.

e. preserving selection.

8. The fitness of a genotype is determined by the

a. average rates of survival and reproduction of individuals with that genotype.

b. individuals that have the highest rates of both survival and reproduction.

c. individuals that have the highest rates of survival.

d. individuals that have the highest rates of reproduction.

e. average reproductive rate of individuals with that genotype.

9. Laboratory selection experiments with fruit flies have demonstrated that

a. bristle number is not genetically controlled.

b. bristle number is not genetically controlled but changes in bristle number are caused by the environment in which the fly is raised.

c. bristle number is genetically controlled but there is little variation on which natural selection can act.

d. bristle number is genetically controlled but selection cannot result in flies having more bristles than any individual in the original population had.

e. bristle number is genetically controlled, and selection can result in flies having more bristles than any individual in the original population had.

10. Disruptive selection maintains a bimodal distribution of bill size in the West African seedcracker because

a. bills of intermediate shapes are difficult to form.

b. the two major food sources of the finches differ markedly in size and hardness.

c. males use their large bills in displays.

d. migrants introduce different bill sizes into the population each year.

e. older birds need larger bills than younger birds.

11. A population is said to be polymorphic for a locus if it has at least

a. three different alleles at that locus.

b. two different alleles at that locus.

c. two genotypes for that locus.

d. three genotypes for that locus.

e. two alleles for that locus, the rarest of which is more common than expected by mutation alone.

Test questions 8

1. The role of oxygen gas in our cells is to

a. catalyze reactions in glycolysis.

b. produce CO₂.

c. form ATP.

d. accept electrons from the electron transport chain.

e. react with glucose to split water.

2. Oxidation and reduction

a. entail the gain or loss of proteins.

b. are defined as the loss of electrons.

c. are both endergonic reactions.

d. always occur together.

e. proceed only under aerobic conditions.

3. NAD+ is

a. a type of organelle.

b. a protein.

c. present only in mitochondria.

d. a part of ATP.

e. formed in the reaction that produces ethanol.

4. Glycolysis

a. takes place in the mitochondrion.

b. produces no ATP.

c. has no connection with the respiratory chain.

d. is the same thing as fermentation.

e. reduces two molecules of NAD+ for every glucose

molecule processed.

5. Fermentation

a. takes place in the mitochondrion.

b. takes place in all animal cells.

c. does not require O2.

d. requires lactic acid.

e. prevents glycolysis.

6. Which statement about pyruvate is not true?

a. It is the end product of glycolysis.

b. It becomes reduced during fermentation.

c. It is a precursor of acetyl CoA.

d. It is a protein.

e. It contains three carbon atoms.

7. The citric acid cycle

a. takes place in the mitochondrion.

b. produces no ATP.

c. has no connection with the respiratory chain.

d. is the same thing as fermentation.

e. reduces two NAD+ for every glucose processed.

8. The electron transport chain

a. operates in the mitochondrial matrix.

b. uses proteins embedded within a membrane.

c. always leads to the production of ATP.

d. regenerates reduced coenzymes.

e. operates simultaneously with fermentation.

9. Compared to anaerobic metabolism, aerobic breakdown ofglucose produces

a. more ATP.

b. pyruvate.

c. fewer protons for pumping in mitochondria.

d. less CO2.

e. more oxidized coenzymes.

10. Which statement about oxidative phosphorylation is not true?

a. It is the formation of ATP by the respiratory chain.

b. It is brought about by the chemiosmotic mechanism.

c. It requires aerobic conditions.

d. In eukaryotes, it takes place in mitochondria.

e. Its functions can be served equally well by fermentation.

For Discussion -1

1. How is it possible for endergonic reactions to proceed in organisms?

2. Consider two proteins: One is an enzyme dissolved in the cytosol, the other is an ion channel in a membrane. Contrast the structures of two proteins, indicating at least two important differences.

3. Plot free energy versus the course of an endergonic reaction and that of an exergonic reaction. Include the activation energy

in both plots. Label Ea and G on both graphs.

4. Consider an enzyme that is subject to allosteric regulation. If a competitive inhibitor (not an allosteric inhibitor) is added to a solution of such an enzyme, the ratio of enzyme molecules in the active form to those in the inactive form increases.

Explain this observation.

5. If you were presented with a radioactively labeled substance, what experiments would you perform to determine whether it enters cells by simple diffusion or active transport?

For Discussion-2

1. Both photosynthetic electron transport and the Calvin– Benson cycle stop in the dark. Which specific reaction stops

first? Which stops next? Continue answering the question “Which stops next?” until you have explained why both pathways have stopped.

2. In what principal ways are the reactions of electron transport in photosynthesis similar to the respiratory chain and oxidative phosphorylation discussed in previous Chapter ? Differentiate between cyclic and noncyclic electron transport in terms of (1) the products and (2) the source of electrons for the reductionof oxidized chlorophyll.

3. The development of what two experimental techniques made it possible to elucidate the Calvin–Benson cycle? How were these techniques used in the investigation?

4. If water labeled with 18O is added to a suspension of photosynthesizing chloroplasts, which of the following compounds will first become labeled with 18O: ATP, NADPH, O2, or 3PG? If water labeled with 3H is added to a suspension of photosynthesizing chloroplasts, which of the same compounds will first become radioactive? If CO2 labeled with 14C is added to a suspension of photosynthesizing chloroplasts, which of those compounds will first become radioactive?

5. The Viking lander was sent to Mars in 1976 to detect signs of life. Explain the rationale behind the following experiments this unmanned probe performed:

a. A scoop of dirt was inserted into a container and 14CO2 was added. After a while during the Martian day, the 14CO2 was removed and the dirt was heated to high temperatures. Scientists monitoring the experiment back on the Earth looked for the release of 14CO2 as a sign of life.

b. The experiment in (a) was performed, except that the dirt was heated to high temperature for 30 minutes and then allowed to cool to Martian temperature right after scooping and before the 14CO2 was added. If experiment (a) released 14CO2, then this experiment should not release it, if living things were present.

For Discussion- 3

1. Trace the sequence of chemical changes that occurs in mammalian brain tissue when the oxygen supply is cut off. The first change is that the cytochrome c oxidase system becomes totally reduced, because electrons can still flow from cytochrome c but there is no oxygen to accept electrons from cytochrome c oxidase. What are the remaining steps?

2. Trace the sequence of chemical changes that occurs in mammalian muscle tissue when the oxygen supply is cut off. (The first change is the same as that in Question 1.)

3. Some cells that use the citric acid cycle and the respiratory chain can also thrive by using fermentation under anaerobic conditions. Given the lower yield of ATP (per molecule of glucose) in fermentation, why can these cells function so efficiently under anaerobic conditions?

4. Describe the mechanisms by which the rates of glycolysis and aerobic respiration are kept in balance with one another.

5. You eat a hamburger that has polysaccharides, proteins and lipids. Using your knowledge of the integration of biochemical pathways, explain how the amino acids in the proteins and glucose in the polysaccharides can end up as fats.

For Discussion - 4

1. Which organelles and other structures are found in both plant and animal cells? Which are found in plant but not animal cells? In animal but not plant cells? Discuss these differences in relation to the activities of plants and animals.

2. Through how many membranes would a molecule have to pass in going from the interior of a chloroplast to the interior of a mitochondrion? From the interior of a lysosome to the outside of a cell? From one ribosome to another?

3. How does the possession of double membranes by chloroplasts and mitochondria relate to the endosymbiosis theory of the origins of these organelles? What other evidence supports the theory?

4. Compare the extracellular matrix of the animal cell with the plant cell wall with respect to composition of the fibrous and nonfibrous components, rigidity and presence of cytoplasmic “bridges.”

5. Plastids and mitochondria may have arisen via endosymbiosis. Propose a hypothesis for the origin of the cell nucleus.

For Discussion - 5

1. How does a nucleus in the G2 phase of the cell cycle differ from one in the G1 phase?

2. Compare the roles of cohesins and condensin in mitosis, meiosis I and meiosis II.

3. Compare and contrast mitosis (and subsequent cytokinesis) in animals and plants.

4. Suggest two ways in which, with the help of a microscope, one might determine the relative duration of the various phases of mitosis.

5. Contrast mitotic prophase and prophase I of meiosis. Contrast mitotic anaphase and anaphase I of meiosis.

6. Compare the sequence of events in the mitotic cell cycle with the sequence in programmed cell death.

For Discussion-6

1. The genetic code is described as degenerate. What does this mean? How is it possible that a point mutation, consisting of the replacement of a single nitrogenous base in DNA by a different base, might not result in an error in protein production?

2. Har Gobind Khorana at the University of Wisconsin synthesized artificial mRNAs such as poly CA (CACA…) and poly CAA (CAACAACAA…). He found that poly CA codes for a polypeptide consisting of threonine (Thr) and histidine (His), in alternation (His–Thr– His–Thr…). There are two possible codons in poly CA, CAC and ACA. One of these must code for histidine and the other for threonine—but which is which? The answer comes from results with poly CAA, which produces three different polypeptides: poly Thr, poly Gln (glutamine) and poly Asn (asparagine). (An artificial messenger can be read, inefficiently, beginning with any point in the chain; there is no specific initiator region.) Thus poly CAA can be read as a polymer of CAA, of ACA, or of AAC. Compare the results of the poly CA and poly CAA experiments and determine which codon codes for threonine and which for histidine.

3. Look back at Question 2. Using the genetic code as a guide, deduce what results Khorana would have obtained had he used poly UG and poly UGG as artificial messengers. In fact, very few such artificial messengers would have given useful results. For an example of what could happen, consider poly CG and poly CGG. If poly CG were the messenger, a mixed polypeptide of arginine and alanine (Arg–Ala–Ala– Arg . . .) would be obtained; poly CGG would give three polypeptides: poly Arg, poly Ala, and poly Gly (glycine). Can any codons be determined from only these data? Explain.

4. Errors in transcription occur about 100,000 times as often as do errors in DNA replication. Why can this high rate be tolerated in RNA synthesis but not in DNA synthesis?

For Discussion-7

1. During the past 50 years, more than 200 species of insects that attack crop plants have become highly resistant to DDT and other pesticides. Using your recently acquired knowledge of evolutionary processes, explain the rapid and widespread evolution of resistance. Propose ways of using pesticides that would slow down the rate of evolution of resistance. Now that use of DDT has been banned in the United States, what do you expect to happen to levels of resistance to DDT among insect populations? Justify your answer.

2. In what ways does artificial selection by humans differ from natural selection in nature? Was Darwin wise to base so much of his argument for natural selection on the results of artificial selection?

3. In nature, mating among individuals in a population is never truly random, immigration and emigration are common, and natural selection is seldom totally absent. Why then, does it make sense to use the Hardy–Weinberg equilibrium, which is based on assumptions known generally to be false? Can you think of other models in science that are based on false assumptions? How are such models used?

4. As far as we know, natural selection cannot adapt organisms to future events. Yet many organisms appear to respond to natural events before they happen. For example, many mammals go into hibernation while it is still quite warm. Similarly, many birds leave the temperate zone for their southern wintering grounds long before winter has arrived. How can such “anticipatory” behaviors evolve?

5. Populations of most of the thousands of species that have been introduced to areas where they were previously not found, including those that have become pests, began with a few individuals. They should therefore have begun with much less genetic variation than the parent populations have. If genetic variation is advantageous, why have so many of these species been successful in their new environments?

6. The flavors of many crop plants have been enhanced by artificial selection that has removed the bad-tasting chemicals with which they defended themselves in the wild. What problems do growing crop plants with reduced chemical defenses pose for modern agriculture?