Question

The Ames Test measures the number of that result from exposure to potential mutagen, and these type of phenotypic variants can be assayed by plating on media that O revertants; lacks histidine mutagens: contains histidine revertants: contains histidine O mutagens, lacks histidine

Answer 1

Ans The Ames test measures the no . Of bacterial colonies that results from exposure to mutagen and these type of phenotypic variants can be assayed by plating on media that

Mutagens contain histidine.

Ames test is a biological assy which assess the mutagenic potetial of a chemical. It utilizes bacteria to test whether the given compound can causes mutation in DNA .This test was developed by Bruce Ames.

Principle ●Ames test uses several strains of bacteria (Salmonella,E.coli) that carry a mutation.

●Point mutations are made in the histidine in Salmonella typhimurium rendering the bacteria incapable of producing the amino acid.

●Culturing His-Salmonella in a media containing chemicals causes mutation in histidine.When mutagenic events occur base substitution occurs that can causereversion of amino acid prototrophy.This is reverse mutation.

●These reverted bacteria will then grow on histidine deficient media

Method :-

◆Isolate the auxotrophic strain of Salmonella typhimurium for histidine .

◆Prepare a test suspension for Salmonella and add histidine also.Histidine is required for bacterial growth.Once histidine depleted only those bacteria mutated to gain the ability to synthesize histidine from colonies.

◆ Also make a test suspension without test chemicals

◆ Incubate the suspension for 37℃ for 20 hours◆

◆Prepare agar plates and spread the suspension on agar plates.

◆Incubate plates at 37℃for 48 hours.

◆After that count the no.of colonies.

The mutagenicity of chemical is proportional to no.of colonies.If there is large no.of colonies on the test plate then such chemicals are mutagens.

possible mutagen a high number of revertants (his- to his+) suggests the mutagen causes mutations rat liver extract plate incubate ! media with minimal histidine plate incubate Salmonella strain (requires histidine) control plate (natural revertants)

While Ames test is used to identify the revert mutations which are present in strains.It can also be used to detect the mutagenicity of environmental samples such as drugs,dye etc.