Instructions

1 points Save Answer QUESTION 1 A GENE221 student carried out the Ames test with histidine-requiring strains of Salmonella typhimurium (strains TA7001-TA7006) and obtained the results in the table below. The bacteria that grow on the plates of minimal medium without histidine are best described as: Number of bacterial colonies per plate TA 7001 TA7002 TA7003 TA7004 TA7005 TA7006 (AT.>GC) (TASAD (TA->GC) (GOAT (CG->ADCG-GC) NO 10 5 7 47 12 18 mutagen Mutagen 120 17 4 10 a. revertants b.wild-type c. mutants d. auxotrophs 1 points Save Answer QUESTION 2 Unless they undergo mutation, the bacteria used in the Ames test are not able to grow unless the growth medium contains the amino acid histidine. This means that these bacteria are: a. auxotrophs Ob.wild-type c. prototrophs d. revertants Question Completion Status: 1 points Save Answer QUESTION 3 A student carried out the Ames test with strain Salmonella typhimurium TA7001 that requires histidine to grow. The bacteria were spread onto agar with no histidine and a paper disk impregnated with 700 ug ethyl methane sulphonate (EMS) placed in the middle. A control plate had a paper disk that did not contain a test compound. Next day, the plate with EMS had 25 colonies on it. The control plate had 12 colonies. What should the student conclude? O a. EMS might cause mutations in strain TA7001 Ob. EMS causes mutations in strain TA7001 OC. EMS does not cause mutations in strain TA7001 Od. The experiment is not well enough designed to allow any conclusions to be drawn 1 points Save Answer QUESTION 4 A student had a culture of Salmonella typhimurium strain TA7001 that are unable to grow unless they are provided with the amino acid histidine. She centrifuged the culture, resuspended the bacteria in PBS buffer and spread 0.1 mL onto a plate of minimal agar that did not contain histidine. Next day the plate had 27 colonies randomly scattered around the agar. These colonies most likely arose from a revertant bacteria in the culture the absence of histidine induced some of the bacteria to have mutations that made them able to grow without histidine C. contamination of the experiment by other bacteria radiation hitting the bacteria on the plate and causing some of them to become able to grow without histidine A GENE221 student carried out the Ames test with histidine-requiring strains of Salmonella typhimurium (strains TA7001-TA7006) and obtained the results in the table below. Why might the plate of TA7004 with no mutagen have so many colonies compared to the other “No mutagen” plates? Number of bacterial colonies per plate: TA7001 TA7002 TA7003 TA 7004 TA7003 TA7006 KAT-GC) (TA->AD (TA->GC) (GOAD (CG->AT (CG->GC) NO 10 47 12 18 mutan Mutagen 120 10 a mutation event early in the growth of the TA7004 culture has resulted in a jackpot culture of bacteria that can grow without histidine b. all three of the above could be true the mutation required for reversion to histidine-independence in strain TA7004 occurs at a high frequency in S. typhimurium Od the culture of TA7004 has become contaminated with bacteria that can grow without histidine 1 points Save Answer QUESTION 6 The Ames test strains can detect the following mutations: AT > GC AT-> TA AT-> CG, CG -> TA.CG-> AT, CG > GC and frameshift mutations. A chemical sodium bananate is known to cause mutations in mice but does not affect any of the strains used in the Ames test. What is the most likely reason that it is not detected as a mutagen in the Ames test? The compound is not mutagenic for bacteria but is converted into a mutagenic compound in mice Ob. It causes mutations (eg GC->TA) that are not detected in the Ames test c. Sodium bananate is not taken up by the bacterial cells d. It is toxic to the bacteria and so revertants cannot grow 1 points Save Answer QUESTION 7 A student carried out the Ames test in a GENE221 practical, using several different compounds that are known to cause mutations. The different test compounds gave different numbers of colonies with Salmonella typhimurium strain TA7001, with numbers of colonies ranging from 11 to 600. The most likely reason for the different numbers of colonies is: a. Different mutagens are taken up by the bacteria with different effectiveness Ob. Different mutagens react differently with DNA and cause different kinds of mutations O c Different amounts of each mutagen were used Od Different mutagens diffuse to different extents 1 points Save Answer QUESTION 8 A student carried out the Ames test using Salmonella typhimurium strain TA7004, with four different test compounds. Next day she examined the plates – which one is likely to have had a mutagen compound present? a. 69 colonies scattered over the plate b. 4 colonies scattered over the plate c. too many colonies to count in a circle around the disk and touching the disk d.46 colonies in a circle around the test disk, with an area of clearing around the disk

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