Question

1. Explain the set-up and outcome of Griffith’s transformation experiment ?
2. Describe the Ames test and how it used to test the mutagenic properties of chemicals    I NEED ANSWERS FOR BOTH QUESTION , THAT IS , ALSO SEPARATE ANSWERS FOR BOTH QUESTIONS 1 AND 2 !!!!

Answer 1

GRIFFITH EXPERIMENT

Griffith experiment was a crucial experiment for the discovery of genetic material in organisms. In 1928, Frederick Griffith conducted this experiment with Streptococcus pneumoniae bacteria.

SET UP : Griffith cultured two strains of S. pneumococcus bacteria - smooth strain or S strain (virulent strain) and rough strain or R strain (non-virulent strain).

OBSERVATION : Griffith injected these strains into the mice and observed -

• On infecting mice with R strain (non-virulent), the mice survived.
• On infecting mice with S strain (virulent strain), the mice died
• On infecting mice with heat killed R strain (non-virulent), the mice survived
• On infected mice with heat-killed S and living R strain, mice lived.

OUTCOME :

From the experiment, Griffith concluded that the R type bacteria was transformed into S type bacteria by inheriting some "tranforming principle" from the heat killed S strain which turned them virulent. He assumed this transforming principle to be the genetic material of the organism.

AMES TEST

Ames test is a bioassay used to evaluate the mutagenic potential of chemicals. The test implies bacteria to detect whether a chemiacl can cause mutations in the genetic material (DNA) of an organism.

PRINCIPLE :

The test implies several strains of Salmonella or E.coli bacteria to carry out a specific mutations. For example S. typhimurium makes mutations in gene coding for histidine while E.coli makes mutations in gene coding for tryptophan which disrupts the production of the respective amino acid in the bacteria. Such organisms (denoted by His- and Trp-) are unable to grow unless supplied the with histidine and tryptophan in the culture media.

METHOD :

These mutants ( His- Salmonella or Trp- E.coli ) are grown in a culture media constituting of certain chemicals where they again mutate the respective histidine coding or tryptophan coding gene so as to restore it's ability to synthesize the corresponding amino acids. (His+ or Trp+), referred to as a reverse mutation.

Ames test can thus be used for evaluating the mutagenic capacity of chemicals.

INTERPRETATION OF THE RESULTS :

• A positive Ames test result may indicate the chemical to be mutagenic.
• Mutagenic capacity being directly linked to colony number can indicate the chemical being mutagenic incase of large colony number observed.