Introduction
The concept of the gene has evolved over time with contributions from various scientists. One of the most influential experiments in understanding the gene’s function was conducted by George Beadle and Edward Tatum in the 1940s. Their work laid the foundation for molecular genetics and introduced the famous concept: “one gene, one enzyme hypothesis.”
Background of the Experiment
Beadle and Tatum worked on the bread mold Neurospora crassa to understand how genes control biochemical reactions. At that time, it was known that genes are inherited and affect physical traits, but their exact function was unclear.
Beadle and Tatum’s Experiment
They exposed Neurospora spores to X-rays to induce mutations. These mutated strains were then grown on minimal media (a basic nutrient medium). Normally, Neurospora can grow on minimal media by synthesizing all essential nutrients itself. However, the mutated strains failed to grow unless certain nutrients like amino acids or vitamins were added.
Key Observations:
- Mutants were unable to produce specific enzymes needed to synthesize nutrients.
- Each mutant had a defect in only one enzyme pathway.
Conclusion of the Study
Based on their findings, Beadle and Tatum proposed that:
- Each gene is responsible for the production of a single enzyme.
- When a gene is mutated, the corresponding enzyme is not produced, affecting the biochemical pathway.
This became known as the “one gene, one enzyme” hypothesis. Later, this was modified to “one gene, one polypeptide” as it became evident that not all proteins are enzymes and some enzymes have multiple polypeptides coded by different genes.
Importance of Their Work
- Established a direct link between genes and biochemical functions
- Helped explain how genetic disorders occur (due to enzyme deficiencies)
- Laid the groundwork for the field of molecular biology
Modern Understanding of Gene
Today, a gene is defined as a sequence of DNA that codes for a functional product, usually a protein. We now know that:
- Genes can be regulated (turned on/off)
- Some genes code for RNA, not proteins
- Genes interact with each other and the environment
Examples in Human Genetics
- Phenylketonuria (PKU): Caused by a defective gene that fails to produce the enzyme phenylalanine hydroxylase
- Albinism: Due to lack of enzyme tyrosinase, required for melanin production
Conclusion
Beadle and Tatum’s experiments marked a turning point in genetics by showing that genes are directly responsible for producing enzymes that control metabolic functions. Their “one gene, one enzyme” hypothesis, though refined, remains a cornerstone in understanding the molecular function of genes. Their work continues to inspire research in genetics, biotechnology, and medicine.