MBIO 2020 Lecture Notes - Lecture 22: Chromosome, Plasmid, Ames Test

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grayrabbit360

10 Nov 2016

School

University of Manitoba

Department

Microbiology

Course

MBIO 2020

Professor

Dibrov Pavel

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Document Summary

Ames test screens for potentially carcinogenic chemicals. If the chemical is mutagenic, his- to his+ revertants will be induced and more his+ colonies will be formed on this plate. Number of colonies formed - indicates mutagenic potential of the chemical. Incubation of chemical with liver extract may be required - since some chemicals are non- carcinogenic until they have been activated by liver enzymes. Hgt or lateral gene transfer - various processes of genetic exchange in bacteria - part of evolution. Eukaryotes carry out genetic exchange during sexual reproduction. Other than mutants - 3 hgt mechanisms to acquire new dna from environment/microorganisms: transformation, transduction, conjugation. Only a portion of genome of donor cell is transferred to recipient cell: donor dna - exogenote dna - recipient genome - endogenote. Upon receiving donor dna, recipient becomes a merozygote - partially diploid - may carry 2 copies of same gene.

Related Questions

1. At Thanksgiving dinner, your great aunt refuses to eat with plastic silverware and proudly exclaims that she has discarded all plastics because âthey cause cancer.â You wonder if chemicals you commonly use are mutagenic. You recall your time in BY 331, Genetics, and realize that you can use the Ames test to test for reversion of a point mutation in the HisG gene in the bacteria S. typhimurium. You added the chemical you wish to test into the growth medium for the bacteria. You carefully plated an equal number of cells on each mutagenesis plate. You also calculated percent survival for chemical treated cells relative to untreated cells. Remember that the plate media for survival is not selective. A summary of the results is shown below.

Chemical	Percent Survival	Number of Revertants (# of His⁺ colonies/selective plate)
No chemical added	100	28
Chemical A	50	1400
Chemical B	70	20
Chemical C	100	7

A. What medium must be used in the selective plate as part of the Ames test? Explain how a mutation gives rise to a revertant in this experiment.

[Type your answer here, use as much space as necessary to completely answer the question]

B. You are initially surprised to see revertants in the absence of any chemical that you are testing, but you realize that this is normal. Explain a specific way in which a revertant can arise in the absence of an added mutagen.

[Type your answer here, use as much space as necessary to completely answer the question]

C. Which chemicals would you identify as containing a mutagen? Explain your reasoning.

[Type your answer here, use as much space as necessary to completely answer the question]

D. Which chemicals would you identify as possibly antimutagenic? Explain your reasoning.

[Type your answer here, use as much space as necessary to completely answer the question]

MBIO 2020 Lecture Notes - Lecture 22: Chromosome, Plasmid, Ames Test

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