Questions and Answers of Principles of Genetics

Fifteen distinct DNA polymerases—α, β, γ, δ, ε, κ, ζ, η, θ, κ, λ, μ, σ, ϕ, and Rev1—have been characterized in mammals. What are the intracellular locations and functions of these
The E. coli chromosome contains approximately 4 × 106 nucleotide pairs and replicates as a single bidirectional replicon in approximately 40 minutes under a wide variety of growth conditions. The
E. coli cells that have been growing in 14N for many generations are transferred to medium containing only 15N and allowed to grow in this medium for four generations. Their DNA is then extracted and
The bacteriophage lambda chromosome has several A:T-rich segments that denature when exposed to pH 11.05 for 10 minutes. After such partial denaturation, the linear packaged form of the lambda DNA
What enzyme activity catalyzes each of the following steps in the semiconservative replication of DNA in prokaryotes?(a) The formation of negative supercoils in progeny DNA molecules. (b) The
One species of tree has a very large genome consisting of 2.0 × 1010 base pairs of DNA.(a) If this DNA was organized into a single linear molecule, how long (meters) would this molecule be? (b)
Why must each of the giant DNA molecules in eukaryotic chromosomes contain multiple origins of replication?
In E. coli, viable polA mutants have been isolated that produce a defective gene product with little or no 5′→3′ polymerase activity, but normal 5′→3′ exonuclease activity. However, no
Other polA mutants of E. coli lack the 3′ → 5′ exonuclease activity of DNA polymerase I. Will the rate of DNA synthesis be altered in these mutants? What effect(s) will these polA mutations
Many of the origins of replication that have been characterized contain AT-rich core sequences. Are these AT-rich cores of any functional significance? If so, what?
(a) Why isn’t DNA primase activity required to initiate rolling-circle replication?(b) DNA primase is required for the discontinuous synthesis of the lagging strand, which occurs on the
DNA polymerase I is needed to remove RNA primers during chromosome replication in E. coli. However, DNA polymerase III is the true replicase in E. coli. Why does not DNA polymerase III remove the RNA
In E. coli, three different proteins are required to unwind the parental double helix and keep the unwound strands in an extended template form. What are these proteins, and what are their respective
How similar are the structures of DNA polymerase I and DNA polymerase III in E. coli? What is the structure of the DNA polymerase III holoenzyme? What is the function of the dnaN gene product in E.
The dnaA gene product of E. coli is required for the initiation of DNA synthesis at oriC. What is its function?How do we know that the DnaA protein is essential to the initiation process?
What is a primosome, and what are its functions? What essential enzymes are present in the primosome? What are the major components of the E. coli replisome? How can geneticists determine whether
The chromosomal DNA of eukaryotes is packaged into nucleosomes during the S phase of the cell cycle. What obstacles do the size and complexity of both the replisome and the nucleosome present during
In what ways does chromosomal DNA replication in eukaryotes differ from DNA replication in prokaryotes?(1) DNA replication usually occurs continuously in rapidly growing prokaryotic cells but is
(a) The chromosome of the bacterium Salmonella typhimurium contains about 4 × 106 nucleotide pairs. Approximately how many Okazaki fragments are produced during one complete replication of the S.
In the yeast S. cerevisiae, haploid cells carrying a mutation called est1 (for ever-shorter telomeres) lose distal telomere sequences during each cell division. Predict the ultimate phenotypic effect
Assume that the sequence of a double-stranded DNA shown below is present at one end of a large DNA molecule in a eukaryotic chromosome.5′-(centromere
Distinguish between DNA and RNA (a) Chemically, (b) Functionally, (c) By location in the cell.
On the basis of what evidence was the messenger RNA hypothesis established?
At what locations in a eukaryotic cell does protein synthesis occur?
List three ways in which the mRNAs of eukaryotes differ from the mRNAs of prokaryotes.
What different types of RNA molecules are present in prokaryotic cells? in eukaryotic cells? What roles do these different classes of RNA molecules play in the cell?
Many eukaryotic genes contain non-coding introns that separate the coding sequences or exons of these genes. At what stage during the expression of these split genes are the noncoding intron
For several decades, the dogma in biology has been that molecular reactions in living cells are catalyzed by enzymes composed of polypeptides. We now know that the introns of some precursor RNA
What role(s) do spliceosomes play in pathways of gene expression? What is their macromolecular structure?
What components of the introns of nuclear genes that encode proteins in higher eukaryotes are conserved and required for the correct excision of intron sequences from primary transcripts by
In human beings, the gene for b-globin is located on chromosome 11, and the gene for a-globin, which is another component of the hemoglobin protein, is located on chromosome 16. Would these two
Perform a chi-square test to determine if an observed ratio of 30 tall to 20 dwarf pea plants is consistent with an expected ratio of 1:1 from the cross Dd × dd.
In pedigree (b) of Problem 3.24, what is the chance that the couple III-1 and III-2 will have an affected child?What is the chance that the couple IV-2 and IV-3 will have an affected child?
What blood types could be observed in children born to a woman who has blood type M and a man who has blood type MN?
In rabbits, coloration of the fur depends on alleles of the gene c. From information given in the chapter, what phenotypes and proportions would be expected from the following crosses: (a) c+c+
In mice, a series of five alleles determines fur color. In order of dominance, these alleles are as follows: AY, yellow fur but homozygous lethal; AL, agouti with light belly; A+, agouti (wild-type);
In several plants, such as tobacco, primrose, and red clover, combinations of alleles in eggs and pollen have been found to influence the reproductive compatibility of the plants. Homozygous
A woman with type O blood gave birth to a baby, also with type O blood. The woman stated that a man with type AB blood was the father of the baby. Is there any merit to her statement?
A woman with type AB blood gave birth to a baby with type B blood. Two different men claim to be the father. One has type A blood, the other has type B blood. Can the genetic evidence decide in favor
The flower colors of plants in a particular population may be blue, purple, turquoise, light blue, or white. A series of crosses between different members of the population produced the following
A woman who has blood type O and blood type M marries a man who has blood type AB and blood type MN. If we assume that the genes for the A-B-O and M-N bloodtyping systems assort independently, what
A Japanese strain of mice has a peculiar, uncoordinated gait called waltzing, which is due to a recessive allele, v. The dominant allele V causes mice to move in a coordinated manner. A mouse
Congenital deafness in human beings is inherited as a recessive condition. In the following pedigree, two deaf individuals, each presumably homozygous for a recessive mutation, have married and
In the fruit fly, recessive mutations in either of two independently assorting genes, brown and purple, prevent the synthesis of red pigment in the eyes. Thus, homozygotes for either of these
The dominant mutation Plum in the fruit fly also causes brownish-purple eyes. Is it possible to determine by genetic experiments whether Plum is an allele of the brown or purple genes?
From information given in the chapter, explain why mice with yellow coat color are not true-breeding.
A couple has four children. Neither the father nor the mother is bald; one of the two sons is bald, but neither of the daughters is bald. (a) If one of the daughters marries a nonbald man and
The following pedigree shows the inheritance of ataxia, a rare neurological disorder characterized by uncoordinated movements. Is ataxia caused by a dominant or a recessive allele? Explain.
Chickens that carry both the alleles for rose comb (R) and pea comb (P) have walnut combs, whereas chickens that lack both of these alleles (i.e., they are genotypically rr pp) have single combs.
Rose-comb chickens mated with walnut-comb chickens produced 15 walnut-, 14 rose-, 5 pea-, and 6 single-comb chicks. Determine the genotypes of the parents.
Summer squash plants with the dominant allele C bear white fruit, whereas plants homozygous for the recessive allele c bear colored fruit. When the fruit is colored, the dominant allele G causes it
The white Leghorn breed of chickens is homozygous for the dominant allele C, which produces colored feathers. However, this breed is also homozygous for the dominant allele I of an independently
Fruit flies homozygous for the recessive mutation scarlet have bright red eyes because they cannot synthesize brown pigment. Fruit flies homozygous for the recessive mutation brown have
Consider the following hypothetical scheme of determination of coat color in a mammal. Gene A controls the conversion of a white pigment P0 into a gray pigment P1; the dominant allele A produces the
What F2 phenotypic segregation ratio would be expected for the cross described in the preceding problem if the dominant allele, C, of the third gene produced a product that completely inhibited the
The Micronesian Kingfisher, Halcyon cinnamomina, has a cinnamon-colored face. In some birds, the color continues onto the chest, producing one of three patterns: a circle, a shield, or a triangle; in
In a species of tree, seed color is determined by four independently assorting genes: A, B, C, and D. The recessive alleles of each of these genes (a, b, c, and d) produce abnormal enzymes that
Multiple crosses were made between true-breeding lines of black and yellow Labrador retrievers. All the F1 progeny were black. When these progeny were inter crossed, they produced an F2 consisting of
Two plants with white flowers, each from true-breeding strains, were crossed. All the F1 plants had red flowers. When these F1 plants were intercrossed, they produced an F2 consisting of 177 plants
Consider the following genetically controlled bio synthetic pathway for pigments in the flowers of a hypothetical plant:Assume that gene A controls the conversion of a white pigment, P0, into another
In the following pedigrees, what are the inbreeding coefficients of A, B, and C? A Offspring of half-first cousins Offspring of first cousins once removed
A, B, and C are inbred strains of mice, assumed to be completely homozygous. A is mated to B and B to C. Then the A × B hybrids are mated to C, and the offspring of this mating are mated to the B ×
Mabel and Frank are half siblings, as are Tina and Tim. However, these two pairs of half siblings do not have any common ancestors. If Mabel marries Tim and Frank marries Tina and each couple has a
Suppose that the inbreeding coefficient of I in the following pedigree is 0.25. What is the inbreeding coefficient of I€™s common ancestor, C? C
A randomly pollinated strain of maize produces ears that are 24 cm long, on average. After one generation of self fertilization, the ear length is reduced to 20 cm. Predict the ear length if
What are the genetic differences between male- and female-determining sperm in animals with heterogametic males?
A male with singed bristles appeared in a culture of Drosophila. How would you determine if this unusual phenotype was due to an X-linked mutation?
In grasshoppers, rosy body color is caused by a recessive mutation; the wild-type body color is green. If the gene for body color is on the X chromosome, what kind of progeny would be obtained from a
What are the sexual phenotypes of the following genotypes in Drosophila: XX, XY, XXY, XXX, XO?
In human beings, a recessive X-linked mutation, g, causes green-defective color vision; the wild-type allele, G,causes normal color vision. A man (a) And a woman (b), Both with normal
If both father and son have defective color vision, is it likely that the son inherited the trait from his father?
A normal woman, whose father had hemophilia, marries a normal man. What is the chance that their first child will have hemophilia?
A man with X-linked color blindness marries a woman with no history of color blindness in her family. Thedaughter of this couple marries a normal man, and their daughter also marries a normal man.
A man who has color blindness and type O blood has children with a woman who has normal color vision and type AB blood. The woman’s father had color blindness. Color blindness is determined by an
A Drosophila female homozygous for a recessive X-linked mutation that causes vermilion eyes is mated to a wildtype male with red eyes. Among their progeny, all the sons have vermilion eyes, and
Suppose that the LCR of the β-globin gene cluster was deleted from one of the two chromosomes 11 in a man. What disease might this deletion cause?
In Drosophila larvae, the single X chromosome in males appears diffuse and bloated in the polytene cells of the salivary gland. Is this observation compatible with the idea that X-linked genes are
Suppose that you used site-specific mutagenesis to modify the trpL sequence such that the two UGG Trp codons at positions 54–56 and 57–60 (Figure 17.14) in the mRNA leader sequence were changed
By what mechanism does the presence of tryptophan in the medium in which E. coli cells are growing result in premature termination or attenuation of transcription of the trp operon?
Constitutive mutations produce elevated enzyme levels at all times; they may be of two types: Oc or I−. Assume that all other DNA present is wild-type. Outline how the two constitutive mutants can
As a genetics historian, you are repeating some of the classic experiments conducted by Jacob and Monod with the lactose operon in E. coli. You use an F plasmid to construct several E. coli strains
Write the partial diploid genotype for a strain that will(a) Produce β-galactosidase constitutively and permease inducibly and (b) Produce β-galactosidase constitutively but not permease
Groups of alleles associated with the lactose operon are as follows (in order of dominance for each allelic series): repressor, Is (superrepressor), I+ (inducible), and I- (constitutive); operator,
In the lactose operon of E. coli, what is the function of each of the following genes or sites:(a) Regulator, (b) Operator, (c) Promoter, (d) Structural gene Z, and (e) Structural
The Streptococcus pyogenes Cas9 endonuclease can be targeted to a specific genomic DNA sequence by an sgRNA that at its 5′ end has 20 nucleotides complementary to the target sequence. If this
How can inducible and repressible enzymes of microorganisms be distinguished?
Distinguish between (a) Repression and (b) Feedback inhibition caused by the end-product of a biosynthetic pathway. How do these two regulatory phenomena complement each other to provide
What would be the result of inactivation by mutation of the following genes or sites in the E. coli lactose operon:(a) Regulator, (b) Operator, (c) Promoter, (d) Structural gene Z,
Assume that you have discovered a new strain of E. coli that has a mutation in the lac operator region that causes the wild-type repressor protein to bind irreversibly to the operator. You have named
Why is the Oc mutation in the E. coli lac operon epistatic to the Is mutation?
For each of the following partial diploids indicate whether enzyme synthesis is constitutive or inducible (see Problem 17.5 for dominance relationships):(a) I+O+Z+Y+/I+O+Z+Y+, (b)
How could the tryptophan operon in E. coli have developed and been maintained by evolution?
Of what biological significance is the phenomenon of catabolite repression?
How might the concentration of glucose in the medium in which an E. coli cell is growing regulate the intracellular level of cyclic AMP?
Is the CAP–cAMP effect on the transcription of the lac operon an example of positive or negative regulation? Why?
Would it be possible to isolate E. coli mutants in which the transcription of the lac operon is not sensitive to catabolite repression? If so, in what genes might the mutations be located?
Using examples, distinguish between negative regulatory mechanisms and positive regulatory mechanisms.
The following table gives the relative activities of the enzymes Î²-galactosidase and Î²-galactoside permease in cells with different genotypes at the lac locus in E. coli. The
The rate of transcription of the trp operon in E. coli is controlled by both (1) repression/derepression and (2) attenuation. By what mechanisms do these two regulatory processes modulate trp operon
What effect will deletion of the trpL region of the trp operon have on the rates of synthesis of the enzymes encoded by the five genes in the trp operon in E. coli cells growing in the presence of

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