Defrosting, Detours, and a Debrief on Evolution

Last week was my first week of summer research. I was actually very excited to come back to campus. Relaxing at home is wonderful and much needed after finals, but with all the time in the world on my hands I started to get a little antsy. At the end of the semester, I paused my experiment by storing my yeast populations in glycerol and freezing them. Freezing the yeast puts them in a dormant state. When I returned for the summer, I knew I would be able to start exactly where I left off. For the first couple of days, all I did was prepare myself to start evolving again by getting all my equipment ready. I grow the yeast in glass tubes filled with evolution medium, basically sugar water. I spent a good portion of Monday autoclaving (sterilizing) and washing old tubes, making evolution medium and filling up clean tubes with it. At the beginning of last week, all but one of the autoclaves in the ISC was broken, so it was quite an adventure having to go back and forth to the third floor to get all my work done.

On Tuesday, I was able to start my experiment. I took the yeast that I had stored out of the freezer. I stored the yeast in a 24-welled plate with each well housing a different population. I scraped some of the yeast out of the wells and pipetted them into clean glass tubes with EM and antibiotics. In total, I have 19 populations, including both sexual and asexual yeast as well as control populations. The yeast take about two days to grow. During this time, I leave them rotating in an incubator. It was actually perfect timing that I did not have anything to do on Wednesday because my lab decided to take advantage of the good weather and take a trip to Busch Gardens.

On Thursday, I inoculated the yeast into glass tubes with EM, antibiotics, and beads (The control populations do not have beads). Some of the tubes from population 7 had not fully grown up yet so I let them stay in the incubator for an extra day and inoculated them on Friday. The way I set up my experiment, I do have to come into the lab everyday to treat the yeast. Over the weekend, I started my first transfer. This involves taking the beads out of the glass tubes the yeast have been growing in, washing and sonicating (shaking) off all the yeast from those beads, and then pipetting just the yeast from the beads into new tubes. This procedure specifically selects for plastic adherence in yeast because I am only allowing the yeast that stuck really well to the plastic bead to reproduce in the next generation. Even though, I’ve been doing this for a whole semester at this point, the procedure is still a little finicky. I have to be really careful not to drop beads because that risks contamination. To help keep track of my daily treatment to the yeast and where I am in the treatment cycle, I created an excel sheet —- Juliana’s Master Record.

That was all for week one! Until next time!

Plates of yeast that had been left in the lab for three weeks. Yes, it does look as bad as it smelled.

Plates of yeast that had been left in the lab for three weeks. Yes, it does look as bad as it smelled.


  1. Wow Juliana, I am really impressed with your work. It must be hard to work with so many populations at once, especially when you must keep everything very sterile to avoid contamination. What are you planning to do once the yeast have finished evolving? Also, what is the purpose of the antibiotic?
    I like that you are using yeast because it is a eukaryotic organism. This way, we can apply more of the evolutionary concepts we see to humans. Though yeast are generally single-celled, it is interesting to see you work with them instead of bacteria. Thanks for posting!