George Beadle & Edward Tatum Experiment

Instructor: Adrianne Baron

Adrianne has taught high school and college biology and has a master's degree in cancer biology.

There are so many discoveries in the field of genetics. Learn how two scientists worked with bread molds in the 1940s to discover an essential property of genes and enzymes.

George Beadle and Edward Tatum

There have been so many astounding discoveries that have helped us to understand and improve our lives. George Beadle and Edward Tatum were two scientists whose work changed how we view the body and detect and treat diseases.

George Beadle was a geneticist and Edward Tatum was a biochemist that both lived and worked in the US. The majority of their studies took place at Columbia University.

What the Experiment Proved

These men are most notably remembered for the George Beadle and Edward Tatum experiment conducted in the 1940s. This study proved that genes are responsible for giving the directions needed to produce enzymes that control metabolic processes.

Let's break that down. Enzymes are proteins that allow chemical reactions to occur at a faster rate. Metabolic processes are chemical reactions that build or break down the various chemical compounds that living organisms need.

Choosing a Test Subject

Before Beadle and Tatum came to this conclusion, they had lots of work to do. Beadle was studying fruit flies. Even though these are very small organisms, they have complex genetic patterns that make it difficult to get results.

Beadle therefore switched to studying a species of bread mold instead. Mold has simpler genetic patterns where certain characteristics are determined by one gene rather than multiple genes like in fruit flies.

Creating and Growing Mutants

Beadle and Tatum started their experiment by creating mutants of the mold they were working with. They did so by exposing mold spores to radiation from x-rays to cause mutations in the DNA. Then they crossed those mutant molds with the regular, unradiated types.

The two hey then transferred the next generation to complete media, which is media with all of the nutrients needed for growth, in this case, sugar, salts, aminio acids, and lots of vitamins. Once the mold grew, they transferred part of the colony to minimal media, which is media that is missing one or more of the nutrients needed to grow, in this case it was missing amino acids and all other vitamins other than biotin.

Methods and Results

Now, this bread mold is known to be able to survive in both types of mediums. It can survive in the minimal media by turning what is available into those other vital building blocks (amino acids).

However, in this experiment, there were some colonies that didn't grow in the minimal media. These were the mutants. They were no longer able to make some missing ingredient to allow them to grow.

To determine which nutrient needed, they separated the colonies that didn't grow and added either vitamins or amino acids back in. The ones that were given the vitamins did not live, so they knew it must be amino acids that were needed. But which one?

They had to test for each of the 20 amino acids to isolate which one would allow for mold growth. They had success with the amino acid arginine.

Experimental Conclusion

Now keep in mind that the spores are just reproductive cells containing DNA. The spores do not contain amino acids. The only thing that could have been mutated in the spores is the DNA of genes.

To make the amino acid arginine, the mold must have a particular enzyme. Beadle and Tatum where thereby able to prove that the mutant cultures were missing the gene that encoded for the specific enzyme that makes arginine.

Their work came to a hypothesis - the one gene one enzyme hypothesis, or that only one gene is needed to make one enzyme. This has since been modified a bit (genes actually code for a single polypeptide, which can technically combine with other genes in making an enzyme).

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