Concept explainers
In an experiment employing the methods of the Ames test, two
a. Characterize the expected distribution of colony growth on the four plates. Defend your growth prediction for each plate.
b. What event is being detected by growth of a colony on any of the four plates?
c. Why is the
d. Suppose the compound being tested was proflavin instead of EMS. Would this change the Ames test results? Explain why or why not.
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- C. Anagnostopoulos and I. P. Crawford isolated and studied a series of mutations that affected several steps in the biosynthetic pathway leading to tryptophan in the bacterium Bacillus subtilis . Seven of the strains that they used in their study are listed here, along with the mutation found in each strain.Strain Mutation T3 T− 168 I− 168PT I− TI I− TII I− T8 A− H25 H− To map the genes for tryptophan synthesis, they carried out a series of transformation experiments on strains having different mutations and determined the percentage of recombinants among the transformed bacteria. Their results were as follows:(refer picture) On the basis of these two-point crosses, determine the order of the genes and the distances between them. Where more than one cross was completed for a pair of genes, average the recombination rates from the different crosses. Draw a map of the…arrow_forwardBacteriophage P22 was used in generalised transduction experiments to infect the Salmonella typhimurium donor strains described in the table below. The resulting phage lysates were then used to infect the recipient strains of S. typhimurium recipient strains listed in the table. In each cross, a phenotype was selected for one of the selected for one of the three genetic markers studied (str, aceA, thrA), and were made to select the recombinants corresponding to the other two markers. markers. The results are given in the following table: Strain I donor str thrA aceA thrA str aceA+ Strain recipient strs thrA+ aceA thrA str aceA Phenotype selected Str Ace+ Str recombinants selected ThrA ThrA ThrA ThrA Ace Ace Number 60 40 95 5 10 90 str: gene involved in streptomycin resistance, aceA: gene involved in the use of acetate as a carbon source, thrA: gene involved in threonine biosynthesis. 1) What are the selective media used in these three transduction experiments? to obtain the selected…arrow_forwarda. Bacteriophage P22 was used in generalized transduction experiments to infect the Salmonella typhimurium donor strains described in the table below. The resulting phage lysates were then used to infect the S. typhimurium recipient strains listed in the table. In each cross, a phenotype was selected for one of the three genetic markers studied (str, aceA, thrA), and then replicates were performed to select the corresponding recombinants for the other two markers. The results are given in the following table: Recipient strain Selected phenotype Selected recombinants Donor strain str thrA aceAt thrA str aceA+ strs thrA+ aceA thrA+ str aceA Str Ace+ Str ThrA ThrA+ ThrA ThrA+ Ace Ace+ str: gene involved in streptomycin resistance, aceA: gene involved in the use of acetate as a carbon source, thrA: gene involved in the biosynthesis of threonine. Number 60 40 95 5 10 90 What are the selective media used in these three transduction experiments, on the one hand to obtain the selected…arrow_forward
- Bacteriophage P22 was used in generalized transduction experiments to infect the Salmonella typhimurium donor strains described in the table below. The resulting phage lysates were then used to infect the S. typhimurium recipient strains listed in the table. In each cross, a phenotype was selected for one of the three genetic markers studied (str, aceA, thrA), and then replicates were performed to select the corresponding recombinants for the other two markers. The results are given in the following table: Recipient strain Selected phenotype Selected recombinants Donor strain str thrA aceA+ thrA str aceA+ strs thrA+ aceA thrA+ str aceA Str Ace+ Str ThrA ThrA+ ThrA ThrA+ Ace Ace str: gene involved in streptomycin resistance, aceA gene involved in the use of acetate as a carbon source, thrA: gene involved in the biosynthesis of threonine. Number 60 40 95 5 10 90 Determine the order of the genes and draw a genetic map showing this orderarrow_forwardSickle cell anaemia is caused by a mutation in the HBB gene. The normal wild-type βA allele contains an MstII restriction site; in the mutated sickle-cell βS allele this restriction site has been lost.PCR amplification of part of the gene encompassing the mutation site from a normal unaffected individual results in a product of 110bp. Digestion of the PCR product with MstII and subsequent gel electrophoresis results in a single band of 55bp. How many bands and of what size would you expect to see in individuals who: i) has sickle-cell anaemia (has two βS alleles) ii) carry the disease (sickle cell trait) (has one βS and one βA allele) a. Individual Number of bands Size of bands (bp) Sickle-cell anaemia(has two βS alleles) 2 55 Sickle cell trait)(has one βS and one βA allele) 1 110 b. Individual Number of bands Size of bands (bp) Sickle-cell anaemia(has two βS alleles) 2 110 Sickle cell trait)(has one βS and one βA allele) 2 55 & 110…arrow_forwardFour Hfr strains (A, B, C, D), were all derived from a F+ strain of E. coli. When each strain is used as a donor in an interrupted-conjugation experiment, the entry times of the first five markers are indicated in the table below (time of entry in minutes is indicated in brackets). Below is a partial map of the F+ strain (distances not proportional). Match the position of all genes with their correct position on this map. Strain A ala+ (5) ser+ (10) ade+ (15) his+ (25) val+ (30) 3 5 2 7 4 1 6 Strain B ade+ (12) his+ (22) val+ (27) pro+ (42) met+ (45) > sert ade+- 1. lac+ his+ ala+ met+ mal+ pro+ val+ Strain C pro+ (1) met+ (6) lac+ (11) mal+ (21) ala+ (31) 7. Strain D met+ (10) pro+ (15) val+ (30) his+ (35) ade+ (45) 2. 6. 3. 5. 4. 1. position #1 2. position #2 3. position #3 4. position #4 5. position #5 6. position #6 7. position #7arrow_forward
- You can carry out matings between an Hfr and F strain by mixing the two cell types in a small patch on a plate and then replica plating to selective medium. This methodology was used to screen hundreds of different cells for a recombination-deficient recA - mutant. Why is this an assay for RecA function? Would you be screening for a recA mutation in the F or Hfr strain using this protocol? Explain.arrow_forwardFour Hfr strains are derived from an F+ strain of E. Coli to serve as donors for an interrupted-mating experiment. Use the time-table and partial map of the F+ strain (shown below) to determine the genes’ respective positions. Keep in mind that the map distances are NOT proportional, only the FIRST 5 markers are indicated per strain, and the entry times, recorded in minutes, are in parentheses. Transferred genes represent wild-type alleles. Based on the data, which gene can be located at position 5 on the map?arrow_forwardDNA from a strain of bacteria with genotype a+ b+ c+ d+ e+ was isolated and used to transform a strain of bacteria that was a− b− c− d− e−. The transformants were tested for the presence of donated genes. The following genes were cotransformed: a+ and d+ b+ and e+ c+ and d+ c+ and e+ What is the order of genes a, b, c, d, and e on the bacterial chromosome?arrow_forward
- From an Escherichia coli strain, five Hfr strains were isolated. The location and orientation of the transfer origin of each Hfr strain is shown in Figure 1. You want to use these five strains to map the locus responsible for thiamine synthesis, called thi. Each Hfr strain is sensitive to rifampicin (Rifs) and thi*. Conjugation experiments are performed between each of the Hfr strains and an F strain Rif Thi™. 0 T leu 10 20 T nadD pyrC trp 40 T his 60 70 2) The results are shown in the following table: Donor strain Hfr1 Hfr2 Hfr3 Hfr4 Hfr5 cysG 80 90 1) What is the selection medium used in these conjugation experiments metA Colonies Thi+ 1000 0 400 0 25 100 Hfr1 Hfr2 Figure 1: Chromosome map of Escherichia coli. Five Hfr strains (Hfr1 to Hfr5) were isolated and the location and orientation of the origin of transfer is shown by the arrows in each Hfr strain. Distances in minutes are shown. Leu: leucine biosynthesis; nadD: NAD biosynthesis; pyrC: pyrimidine biosynthesis; trp: tryptophan…arrow_forwardFrom one Escherichia coli strain, five Hfr strains were isolated. The location and orientation of the origin of transfer of each Hfr strain are shown in Figure 1. want to use these five strains to map the locus responsible for thiamine synthesis, called thi. Each Hfr strain is sensitive to rifampicin (RifS) and Thi+. Conjugation experiments are performed between each of the Hfr strains and an F- RifR Thi 9 leu 10 20 30 nadD pyrC trp 40 his 50 60 70 cysG 80 90 metA 100 Hfr1 Hfr2 Hfr3 Hfr4 Hfr5 Figure 1: Chromosome map of Escherichia coli. Five Hfr strains (Hfr1 to Hfr5) were isolated and the location and orientation of the origin of transfer is shown by the arrows in each Hfr strain. Distances in minutes are indicated. Leu: leucine biosynthesis; nadD: NAD biosynthesis; pyrC: pyrimidine biosynthesis; trp: tryptophan biosynthesis; his: histidine biosynthesis; cysG: cysteine biosynthesis; metA: biosynthesis of methionine. 1) What is the selection medium used in these conjugation…arrow_forwardFrom one Escherichia coli strain, five Hfr strains were isolated. The location and orientation of the origin of transfer of each Hfr strain are shown in Figure 1. want to use these five strains to map the locus responsible for thiamine synthesis, called thi. Each Hfr strain is sensitive to rifampicin (RifS) and Thi+. Conjugation experiments are performed between each of the Hfr strains and an F- RifR Thi leu 10 20 T nadD pyrC trp 30 his Donor strain Hfr1 Hfr2 Hfr3 Hfr4 Hfr5 The results are shown in the following table 60 70 cysG Colonies Thi 1000 0 400 0 25 80 90 metA 1,00 Hfr1 Hfr2 Figure 1: Chromosome map of Escherichia coli. Five Hfr strains (Hfr1 to Hfr5) were isolated and the location and orientation of the origin of transfer is shown by the arrows in each Hfr strain. Distances in minutes are indicated. Hfr 3 Leu: leucine biosynthesis; nadD: NAD biosynthesis; pyrC: pyrimidine biosynthesis; trp: tryptophan biosynthesis; his: histidine biosynthesis; cysG: cysteine biosynthesis; metA…arrow_forward
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