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The Molecular Biology of Eukaryotes Practice Test (page 2)

By — McGraw-Hill Professional
Updated on Aug 23, 2011

The Molecular Biology of Eukaryotes Questions

  1. The haploid genome of Drosophila melanogaster contains approximately 1.8 × 108 nucleotide pairs. The chromosomes of a polytene nucleus collectively have about 5000 bands. Assuming that 95% of the DNA is located in these bands and 5%is in the interband regions     (a)  determine the average number of nucleotide pairs in each band and interband region and     (b)  estimate the average number of genes per band and interband if an average gene contains 103 nucleotide pairs.
  2. The puffing pattern of Drosophila polytene chromosomes seems to change in a predictable pattern during larva development.     (a)  It has been suggested that these puffs are the sites of genes transcription. How could this hypothesis be tested experimentally?     (b)  The synthesis of a particular protein coincides with the appearance of a specific puff in one of the polytene chromosomes. What inference can be made from this observation?
  3. A sex-linked mutation in humans results in deficiency of the enzyme glucose-6-phosphate dehydrogenase (G6PD). Some individuals with this enzyme defect are more resistant to malaria than are those without this enzyme defect. Among those parasitized, approximately half of the blood cells of the resistant females contain the causative parasite; the cells of G6PD-deficient males are not parasitized. How can these observations be explained?
  4. Different mRNA molecules have characteristic half-lives. Propose a method for estimating the half-life of a specific mRNA.
  5. If a certain protein is found in the Golgi apparatus, how can you explain the fact that its cytoplasmic mRNA transcript contains 24 codons at its 5' end that are not represented by corresponding amino acids at the amino terminus of the protein?
  6. The gonads of Drosophila develop from material in the posterior end of the oocyte cortex (outer layer) that contains densely staining polar granules. An autosomal recessive mutation gs, when homozygous, causes adult females to produce oocytes without polar granules; progeny that develop from such eggs do not develop gonads. If parents are of genotype gs+/gs, predict the results for the next two generations.
  7. A mutant gene in Drosophila called antennapedia causes legs to develop on the head where antennae normally appear. To what class of developmental control genes does antennapedia belong? Offer an explanation as to how this mutation might cause abnormal development.
  8. A female fruit fly is homozygous recessive for a mutation in a maternal effect gene important for embryonic development (m/m).     (a)  What kind of offspring will this fly produce when mated to a wild type male (m+ /m+)?     (b)  What kind of offspring will be produced by a male that is homozygous recessive for the same mutation when mated to a wild-type female?     (c)  How is it possible to generate this female fly (m/m) from a cross involving a homozygous recessive parent?
  9. A female fruit fly is heterozygous recessive for a mutation in a zygotic gene important for embryonic development (z+/z).     (a)  What kind of offspring will this fly produce when mated to a wild-type male (z+/z+)?     (b)  What kind of offspring will this fly produce when mated to a male heterozygous for the same mutation?     (c)  Is it possible to isolate a mature fly that is homozygous recessive for a zygotic gene mutation? Explain.
  10. The bicoid protein (see Example 13.20) is localized to the anterior portion of the Drosophila oocyte by the action of two proteins swallow and exuperantia.     (a)  What effect would a mutation in the swallow gene have on embryonic development?     (b)  How would this effect be altered in a fly containing a mutation in both the swallow and the nanos genes?
  11. (a)  Design a mutant screen to identify dominant (gain-of-function) mutations in maternal effect genes in Drosophila.     (b)  Design a screen to identify recessive zygotic gene mutations.
  12. The Drosophila gene hunchback (see Example 13.20) contains five repeats of 5'-TCTAATCCCC-3' in its promoter. Bicoid protein is known to bind to each of these sites. When all five sites are bound with bicoid, maximal transcriptional activation occurs. What would be the phenotype of a fly that contains a deletion of three of the five repeats?
  13. Why are translation controls less critical for eukaryotic genes than for many prokaryotic genes?
  14. The ced-3 gene (see Example 13.22) is required for apoptosis in C. elegans.     (a)  How would a loss-of-function mutation in this gene effect C. elegans development?     (b)  What about a gain-of-function mutation?     (c)  Is there likely to be a human oncogene counterpart to the ced-3 gene?
  15. The N terminus of a polypeptide destined to cross a membrane contains a signal sequence or signal peptide that is removed by a signal peptidase enzyme sometime during the passage of the rest of the polypeptide through the membrane.     (a)  What kinds of amino acids would be expected to predominate in the signal peptide?     (b)Why is protein translocation through the mitochondrial or chloroplast membranes potentially more complex than that through the endoplasmic reticulum?     (c)  In what major respect does the nuclear membrane differ from the membranes of other organelles?
  16. The concentration of cytoplasmic mRNA is observed to be higher under one condition when compared with another. Does this observation indicate that transcription control of that gene is operative? Explain.
  17. Pseudogenes are nontranscribed DNA sequences that are highly homologous in nucleotide sequence to functional genes found elsewhere in the same genome. One class of pseudogenes, known as "processed pseudogenes," is characterized by absence of introns and upstream promoter sequences and presence of 3' terminal poly-A tracts. Propose a mechanism that might account for the origin of processed pseudogenes.
  18. The diagram below represents a spread of nucleolar chromatin, showing gene transcription on a segment of DNA containing a tandemly arranged series of nucleolar rRNA genes. They give the appearance of a linear series of Christmas-tree-like structures, first identified in electron micrographs by O. L. Miller and B. R. Beatty (1969), and have been subsequently referred to as "Miller trees." Identify the following structures or regions.     (a)  The limits of an rRNA gene for the 38S rRNA precursor molecule.     (b)  A nontranscribed spacer DNA region between the rDNA repeats.     (c)  Promoter or initiator region.     (d)  Terminator of an rDNA gene.     (e)  RNA polymerase molecules.     (f )  5' end of an rRNA transcript.     (g)  Do you expect to find ribosomes?     (h)  Is a similar phenomenon expected in E. coli? If so, explain any predicted differences.
  19. Supplementary Problems

  20. A recessive chromosomal gene produces green and white stripes in the leaves of maize, a condition called "japonica." This gene behaves normally in monohybrid crosses giving a 3 green : 1 striped ratio. Another striped phenotype was discovered in Iowa, named "iojap" (a contraction of Iowa and japonica), which is produced by a recessive gene ij when homozygous. If a plant with iojap striping serves as the seed parent, then the progeny will segregate green, striped, and white in irregular ratios regardless of the genotype of the pollen parent. Backcrossing striped progeny of genotype Ij/ij to a green pollinator of genotype Ij/Ij produces progeny that continue to segregate green, striped, and white in irregular ratios. White plants die due to lack of functional chloroplasts. Green plants produce only green progeny except when the genotype of the progeny is ij/ij; striping then reappears. Interpret this information to explain the inheritance of iojap.
  21. If a woman contracts German measles during the first trimester of pregnancy, the child may be seriously affected even though the mother herself suffers no permanent physical effects. Such anomalies as heart and liver defects, deafness, cataracts, and blindness often occur in the affected children at birth. Can these phenotypic results be considered hereditary abnormalities?
  22. A snail produced by a cross between two individuals has a shell with right-hand twist (dextral). This snail produces only left-hand (sinistral) progeny by selfing. Determine the genotype of this snail and its parents. See Solved Problem 13.2.
  23. Most strains of Chlamydomonas (Fig. 5-1) are sensitive to streptomycin (see Example 13.25). A strain is found that requires streptomycin in the culture medium for its survival. How could it be determined whether streptomycin-dependence is due to a chromosomal gene or to a cytoplasmic element?
  24. A yeast (Fig. 6-4) culture, when grown on medium containing acriflavine, produces numerous minute cells that grow very slowly. How could it be determined whether the slow growth was due to a cytoplasmic factor or to a nuclear gene?
  25. Determine the genotypes and phenotypes of sexual progeny in Neurospora from the following crosses:     (a)  fast-poky male × normal female of genotype F',     (b)  poky female × fast-poky male,     (c)  fast-poky female × poky male (see Solved Problem 13.4).
  26. The cells of a Neurospora mycelium are usually multinucleate. Fusion of hyphae from different strains results in the exchange of nuclei. A mycelium that has genetically different nuclei in a common cytoplasm is called a heterokaryon. Moreover, the union results in a mixture of two different cytoplasmic systems called a heteroplasmon or a heterocytosome. The mycelia of two slow-growing strains, each with an aberrant cytochrome spectrum, fuse to form a heteroplasmon that exhibits normal growth. Abnormal cytochromes a and b are still produced by the heteroplasmon. Offer an explanation for this phenomenon.
  27. Male sterile plants (Solved Problem 13.5) in corn may be produced either by a chromosomal gene or by a cytoplasmic factor.     (a)  At least 20 different male-sterile genes are known in maize, all of which are recessive. Why? Predict the F1 and F2 results of pollinating     (b)  a genetic male sterile by a normal, and     (c)  a cytoplasmic male sterile by a normal.
  28. Given seed from a male sterile line of corn (see Solved Problem 13.5), how would you determine if the sterility was genic or cytoplasmic?
  29. A bacterial spirochaete that is passed to the progeny only from the maternal parent has been found in Drosophila willistoni. This microorganism usually kills males during embryonic development but not females. The trait is called "sex ratio" (SR) for obvious reasons. Occasionally, a son of an SR female will survive. This allows reciprocal crosses to be made. The SR condition can be transferred between D. equinoxialis and D. willistoni. The spirochaete is sensitive to high temperatures, which inactivates them, forming "cured" strains with a normal sex ratio.     (a)  What would you anticipate to be the consequence of repeated backcrossing of SR females to normal males?     (b)  A "cured" female is crossed to a rare male from an SR culture. Would the sex ratio be normal? Explain.
  30. How will the sequencing of whole genomes change the way that geneticists approach the understanding of gene structure and function?
  31. The evolution of mitochondrial DNA occurs at a rate much faster than that of nuclear DNA. Hence, there is much greater variation from one person to another in mitochondrial DNA sequences than in nuclear DNA sequences. Of all the existing human populations, there appears to be greater variation in those of Africa than any other place on Earth. Furthermore, all the human mitochondrial DNA sequences can be arranged into a single phylogenetic tree. Assuming that the mitochondrial DNA of our most ancient ancestors had the same amount of individual variation as that of modern mitochondrial DNA, what are the evolutionary implications of these facts?
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