Background on George Wells Beadle and Edward Lawrie Tatum.
George Wells Beadle was born in Wahoo Nebraska October 22, 1903. Beadle would have become a farmer like his father if one of his teachers had not gotten Beadle into science. George Beadle went to University of Nebraska and studied hybrid wheat. Edward Lawrie was born in Boulder Colorado on December 14, 1909. Edward Tatum was educated at the University of Chicago and Wisconsin and majored in biochemistry. Tatum worked on nutrition and metabolism for bacteria which later was the foundation of his later work with Beadle. Tatum and Beadle are both well known for the Genetic Control of Biochemical Reactions in Neurospora
Hypothesis
Beadle & Tatum formulated a hypothesis known as the One Gene-One Enzyme Hypothesis.
One Gene-One Enzyme Hypothesis: Genes act through the production of enzymes, with each gene responsible for producing a single enzyme that in turn affects a single step in a metabolic pathway.
Method
According to their One Gene-One Enzyme hypothesis, it should be possible to create genetic mutants in Nuerospora, a bread mold, that are unable to carry out a specific enzymatic reaction/reaction in the metabolic pathway, more specifically that are unable to synthesize growth factors,like vitamins, amino acids, and other essential products. To prove this Beadle & Tatum exposed Nuerospora, to radiation,in the form of x-rays.The mold was then checked for nutritional mutations by transferring them into a minimal medium,that required the organism carry on all essential syntheses of which it is capable, as opposed to a complete medium that contains all of the normally synthesized products of the organism. The mold samples that did not grow when placed in the minimal medium, didn't grow due to mutations that prevented the synthesis of a specific growth factor.These samples are then tested to figure out what substance they're unable to synthesize by attempting to grow them with the minimal medium, with the addition of either known vitamins, amino acids or, substituting the glucose.Once the substance whose synthesis was being blocked was identified they compared the growth rate of normal strains of Nuerospora to the mutated strains by growing them on similar mediums except that the normal strains' medium didn't contain the substance the other couldn't synthesize.The strain was then crossed over with normal cells, the new cells were tested for the presence or absence of mutation to ascertain whether the mutation was inherited like a normal gene.
Result
One of the mutated strains created was unable to synthesize the vitamin B6. When transferred into a minimal medium containing 1 micro gram or more of synthetic vitamin B6 per 25 cc of medium, it would grow at a similar growth rate and characteristics as a normal strain grown in a similar medium with no B6. Out of the 24 asci crossed only 7 germinated.
Conclusion
Beadle and Tatum results proved that x-rays can induce mutation in genes concerned with control of specific biochemical process. The only difference between the mutated strains and normal strains, was the inability to synthesize that specific metabolite.The cross over of mutant and normal followed single gene-single gene pattern. This proved their one gene-one enzyme hypothesis as the mutated gene affected the enzyme, in turn affecting a specific process, in this case the synthesis of vitamin B6.
