The conditions outlined in the Hardy-Weinberg equilibrium provide parameters, or variables, that can be probed by the experimental scientist. Testing these parameters, or variables, in lab experiments presents several challenges in terms of space, time and resources. Bacteria can be a good model system for these experiments as they have short generational time and their small size allows investigation of populations rather than individuals. Phenotypes of bacteria are often easily selected for and identified, allowing for rapid and cost effective determination of changes in allele frequency. One experiment utilizing multiple populations of the bacteria E. coli ran continuously for close to 20 years and over 30,000 generations (Blount, 2008). The differences in the evolving population include both changes in existing allele frequencies and mutations. The latter genotypes of E. coli do not necessarily represent the absolute best genotypes for the environment; however, genotypes that predominate in latter generations are better suited for their environment than the ones predominating in previous generations.
Such an ambitious experiment is outside of the scope of a student laboratory; however, shorter term experiments can be informative. In this lab we will manipulate E. coli populations so they can be studied in multiple environments. This approach has been used as part of a strategy to understand a problem in world health, antibiotic drug resistance. This week we will create a stock plate of E. coli. In the following weeks, we will use this stock plate to create genetically identical plates of E. coli on differing substrates.
Please read the following procedures carefully to avoid contaminating your bacterial samples. Copy the method in your lab notebook so you can follow this procedure during lab.