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Questions and Answers of Biology

A danger in computing heritability values from studies involving genetically related individuals is the possibility that these individuals share more similar environments than do unrelated
A large, genetically heterogeneous group of tomato plants was used as the original breeding stock by two different breeders, named Mary and Hector. Each breeder was given 50 seeds and began an
The correlation coefficients for height were determined for 15 pairs of individuals with the following genetic relationships: Mother-daughter: 0.36 Mother-granddaughter: 0.17 Sister-sister:
An animal breeder had a herd of sheep with a mean weight of 254 pounds at 3 years of age. He chose animals with mean weights of 281 pounds as parents for the next generation. When these offspring
The trait of blood pressure in humans has a frequency distribution that is similar to a normal distribution. The following graph shows the ranges of blood pressures for a selected population of
The abdomen length (in millimeters) was measured in 15 male Drosophila, and the following data were obtained: 1.9, 2.4, 2.1, 2.0, 2.2, 2.4, 1.7, 1.8, 2.0, 2.0, 2.3, 2.1, 1.6, 2.3, and 2.2. Calculate
In one strain of cabbage, you conduct an RFLP analysis of head weight; you determine that seven QTLs affect this trait. In another strain of cabbage, you find that only four QTLs affect this trait.
From an experimental viewpoint, what does it mean to say that an RFLP is associated with a trait? Let's suppose that two strains of pea plants differ in two RFLPs that are linked to two genes
Let's suppose that two strains of pigs differ in 500 RFLPs. One strain is much larger than the other. The pigs are crossed to each other, and the members of the F1 generation are also crossed among
Outline the steps you would follow to determine the number of genes that influence the yield of rice. Describe the results you might get if rice yield is governed by variation in six different genes.
In a wild strain of tomato plants, the phenotypic variance for tomato weight is 3.2 g2. In another strain of highly inbred tomatoes raised under the same environmental conditions, the phenotypic
The average thorax length in a Drosophila population is 1.01 mm. You want to practice selective breeding to make larger Drosophila. To do so, you choose 10 parents (5 males and 5 females) of the
In a strain of mice, the average 6-week body weight is 25 g and the narrow-sense heritability for this trait is 0.21. A. What would be the average weight of the offspring if parents with a mean
Discuss why heritability is an important phenomenon in agriculture.
From a biological viewpoint, speculate as to why many traits seem to fit a normal distribution. Students with a strong background in math and statistics may want to explain how a normal distribution
What is heterosis? Discuss whether it is caused by a single gene or several genes. Discuss the two major hypotheses proposed to explain heterosis. Which do you think is more likely to be correct?
What is a prophage, a provirus, and an episome? What is their common role in a viral reproductive cycle?
What key features distinguish the lytic from the lysogenic cycles?
With regard to promoting the lytic or lysogenic cycle, what would happen if the following genes were missing from the λ genome? A. cro B. cI C. cII D. int E. cII and cro
How do the λ repressor and the cro protein affect the transcription from PR and PRM? Explain where these proteins are binding to cause their effects.
In your own words, explain why it is necessary for the cl gene to have two promoters. What would happen if it had only PRE?
Figure 17.10 shows a genetic switch that controls the choice between the lytic and lysogenic cycles of phage X. What is a genetic switch? Compare the roles of a genetic switch and a simple operator
What structural features are common to all viruses? Which features are found only in certain types of viruses?
Why is gap repair synthesis needed during HIV DNA integration?
Compare and contrast the roles of fully spliced, incompletely spliced, and unspliced HIV RNA. Which type is needed in the early stages of HIV proliferation, and which is needed in later stages?
Describe the role of Gag polyprotein during the assembly of HIV components at the plasma membrane.
How does an HIV particle acquire its envelope?
Explain the role of HIV protease during the process of HIV maturation.
What are the similarities and differences among viral genomes?
What is a viral envelope? Describe how it is made.
What do the terms host cell and host range mean?
Describe why the attachment step in a viral reproductive cycle is usually specific for one or just a few cell types.
Compare and contrast the entry step of the viral reproductive cycle of phage λ and HIV.
Discuss how researchers determined that TMV is a virus that causes damage to plants.
This question combines your knowledge of conjugation (described in Chapter 7) and the genetic regulation that directs the phage λ reproductive cycles. When researchers mix donor Hfr strains with
What is a reconstituted virus?
Following the infection of reconstituted viruses on tobacco leaves, what two characteristics did Fraenkel-Conrat and Singer analyze? Explain how their results were consistent with the idea that the
Experimentally, when an E. coli bacterium already has a λ prophage integrated into its chromosome, another λ phage cannot usually infect the cell and establish the lysogenic or lytic cycle. Based
A bacterium is exposed to a drug that inhibits the N protein. What would you expect to happen if the bacterium was later infected by phage λ? Would phage λ follow the lytic cycle, the lysogenic
Discuss the properties of emerging viruses. What are the challenges associated with combating them?
Certain environmental conditions such as UV light are known to activate lysogenic λ prophages and cause them to progress into the lytic cycle. UV light initially causes the repressor protein to be
For each of the following mutations, is it a transition, transversion, addition, or deletion? The original DNA strand is 5'-GGAC TAG AT AC-3' A. 5'-GAACTAGATAC-3' B. 5'-GGACTAGAGAC-3' C.
Explain two ways that a chromosomal rearrangement can cause a position effect.
Is a random mutation more likely to be beneficial or harmful? Explain your answer.
Which of the following mutations could be appropriately described as a position effect? A. A point mutation at the -10 position in the promoter region prevents transcription. B. A translocation
Discuss the consequences of a germ-line versus a somatic mutation.
Draw and explain how alkylating agents alter the structure of DNA.
Explain how a mutagen can interfere with DNA replication to cause a mutation. Give two examples.
What type of mutation (transition, transversion, or frameshift) would you expect each of the following mutagens to cause? A. Nitrous acid B. 5-Bromouracil C. Proflavin
Explain what happens to the sequence of DNA during trinucleotide repeat expansion (TNRE). If someone was mildly affected with a TNRE disorder, what issues would be important when considering possible
Distinguish between spontaneous and induced mutations. Which are more harmful? Which are avoidable?
A gene mutation changes an AT base pair to a GC pair. This causes a gene to encode a truncated protein that is nonfunctional. An organism that carries this mutation cannot survive at high
Are mutations random events? Explain your answer.
Trinucleotide repeat expansions (TNREs) are associated with several different human inherited diseases. Certain types of TNREs produce a long stretch of glutamines (an amino acid) within the encoded
What is the difference between the mutation rate and the mutation frequency?
Achondroplasia is a rare form of dwarfism. It is caused by an auto-somal dominant mutation within a single gene. Among 1,422,000 live births, the number of babies born with achondroplasia was 31.
A segment of DNA has the following sequence: TTGGATGCTGG AACCTACGACC A. What would be the sequence immediately after reaction with nitrous acid? Let the letters H represent hypoxanthine and U
In the treatment of cancer, the basis for many types of chemotherapy and radiation therapy is that mutagens are more effective at killing dividing cells than nondividing cells. Explain why. What are
An individual carries a somatic mutation that changes a lysine codon into a glutamic acid codon. Prior to acquiring this mutation, the individual had been exposed to UV light, proflavin, and
Which of the following examples is likely to be caused by a somatic mutation? A. A purple flower has a small patch of white tissue. B. One child, in a family of seven, is an albino. C. One apple
How would nucleotide excision repair be affected if one of the following proteins was missing? Describe the condition of the DNA if repair had been attempted in the absence of the protein. A. UvrA B.
During mismatch repair, why is it necessary to distinguish between the template strand and the newly made daughter strand? How is this accomplished?
What are the two main mechanisms by which cells repair double-strand breaks? Briefly describe each one.
With regard to the repair of double-strand breaks, what are the advantages and disadvantages of homologous recombination repair versus non-homologous end joining?
When DNA N-glycosylase recognizes thymine dimers, it detects only the thymine located on the 5' side of the thymine dimer as being abnormal. Draw and explain the steps whereby a thymine dimer is
What is the underlying genetic defect that causes xeroderma pigmentosum? How can the symptoms of this disease be explained by the genetic defect?
Three common ways to repair changes in DNA structure are nucleotide excision repair, mismatch repair, and homologous recombination repair. Which of these three mechanisms would be used to fix the
Discuss the similarities and differences between the nucleotide excision repair and mismatch repair systems.
In E. coli, a methyltransferase enzyme encoded by the dam gene recognizes the sequence 5' GATC-3' and attaches a methyl group to the N6 position of adenine. E. coli strains that have the dam gene
How would each of the following types of mutations affect the amount of functional protein that is expressed from a gene? A. Nonsense B. Missense C. Up promoter mutation D. Mutation that affects
X-rays strike a chromosome in a living cell and ultimately cause the cell to die. Did the X-rays produce a mutation? Explain why or why not.
Lactose permease is encoded by the lacY gene of the lac operon. A mutation occurred at codon 64 that changed the normal glycine codon into a valine codon. The mutant lactose permease is unable to
Nonsense suppressors, which are described in solved problem SI, tend to be very inefficient at their job of allowing readthrough of a stop codon. How would it affect the cell if they were efficient
Are each of the following mutations silent, missense, nonsense, or frameshift mutations? The original DNA strand is 5'-ATGGGACTAGATACC-3'. A. 5'-ATGGGTCTAGATACC-3' B. 5'-ATGCGACTAGATACC-3' C.
In Chapters 12 through 16, we discussed many sequences that are outside the coding sequence and are important for gene expression. Look up two of these sequences and write them out. Explain how a
Explain how the technique of replica plating supports the random mutation theory but conflicts with the physiological adaptation hypothesis.
Outline how you would use the technique of replica plating to show that antibiotic resistance is due to random mutations.
From an experimental point of view, is it better to use haploid or diploid organisms for mutagen testing? Consider the Ames test when preparing your answer.
How would you modify the Ames test to discover physical mutagens? Would it be necessary to add the rat liver extract? Explain why or why not.
During an Ames test, bacteria were exposed to a potential mutagen. Also, as a control, another sample of bacteria was not exposed to the mutagen. In both cases, 10 million bacteria were plated and
Richard Boyce and Paul Howard-Flanders conducted an experiment that provided biochemical evidence that thymine dimers are removed from DNA by a DNA repair system. In their studies, bacterial DNA was
In E. coli, a variety of mutator strains have been identified in which the spontaneous rate of mutation is much higher than in normal strains. Make a list of the types of abnormalities that could
Discuss the times in a persons life when it would be most important to avoid mutagens. Which parts of a persons body should be most protected from mutagens?
A large amount of research is aimed at studying mutation. However, there is not an infinite amount of research money. Where would you put your money for mutation research? A. Testing of potential
Describe the similarities and differences between homologous recombination involving sister chromatid exchange (SCE) and that involving homologs. Would you expect the same types of proteins to be
In recombinant chromosomes, where is gene conversion likely to take place: near the breakpoint or far away from the breakpoint? Explain.
What events does the RecA protein facilitate?
According to the double-strand break model, does gene conversion necessarily involve DNA mismatch repair? Explain.
Briefly describe three ways that antibody diversity is produced.
Describe the function of RAG1 and RAG2 proteins and NHEJ proteins.
According to the scenario shown in Figure 19.7, how many segments of DNA (one, two, or three) are removed during site-specific recombination within the gene that encodes the K (kappa) light chain for
Describe the role that integrase plays during the insertion of λ DNA into the host chromosome.
If you were examining a sequence of chromosomal DNA, what characteristics would cause you to believe that the DNA contained a transposable element?
The molecular mechanism of SCE is similar to homologous recombination between homologs except that the two segments of DNA are sister chromatids instead of homologous chromatids. If branch migration
Why does transposition always produce direct repeats in the chromosomal DNA?
Which types of TEs have the greatest potential for proliferation: insertion elements, simple transposons, or retrotransposons? Explain your choice.
Let's suppose that a species of mosquito has two different types of simple transposons that we will call X elements and Z elements. The X elements appear quite stable. When analyzing a population of
This chapter describes different types of TEs, including insertion elements, simple transposons, LTR retrotransposons, and non-LTR retrotransposons. Which of these four types of TEs would have the
What features distinguish a transposon from a retrotransposon? How are their sequences different, and how are their mechanisms of transposition different?
Solved problem S2 illustrates the consequences of crossing over between the direct and inverted repeats within a single TE. The drawing here shows the locations of two copies of the same TE within a

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