Gene Expression

Principles Module 50


  • Describe the design of the Beadle and Tatum experiment and how it provides evidence for the one gene, one polypeptide hypothesis
  • Explain the central dogma

Key points

How are traits linked to inheritance?

  • Beadle and Tatum used Neurospora to study the relationship between DNA and traits
  • they mutagenized spores and isolated colonies that couldn’t grow on minimal media (known as auxotrophic mutants)
  • they transferred spores of auxotrophic mutants to arginine media and noted those that recovered, reasoning that they must be mutants in one of the steps of arginine biosynthesis
  • they subcultured their mutants on media supplemented with an intermediate in the pathway and found classes of mutations that recovered:
    • some recovered on media with ornithine, the first intermediate in the pathway
    • some recovered on citruline, the second intermediate
    • some only recovered on arginine, the product of the pathway
  • their interpretation of their results was that each class of mutation corresponded to the loss of a specific enzyme in the pathway, and that by supplying the product of that enzyme they could rescue the growth on minimal media
  • they concluded that one gene dictates the production of one enzyme, now revised to state that one gene dictates one polypeptide
Central dogma
  • the idea that DNA encodes RNA, which in turn encodes proteins
  • DNA is an information storing molecule, and the information it stores often is the instruction set for building a specific protein via messenger RNA (mRNA)
  • DNA also encodes other forms of RNA that are catalytic or structural (ribosomal and transfer RNA)

In-class activities

Questions for Practice