From DNA to Organism: A Study in DNA Function for the High School Biology Classroom
 
 

Module 4: Yeast and the gene

Qualitative analysis (There are two different ways to do this section of the module; this is the qualitative one)

     Tips for culturing yeast cells

  1. Start with 100ml of your yeast solution in a tube. Label the tube 10%. Add to it 900ml of distilled water. Mix gently.

  2. Take 100ml of the 10% yeast solution and put it into a second tube. Label this tube 1%. Add to it 900ml of distilled water. Mix gently.

  3. Take 100ml of the 1% yeast solution and put it into a third tube. Label this tube 0.1%. Add to it 900ml of distilled water. Mix gently.

  4. Take 100ml of the 0.1% yeast solution and put it into a fourth tube. Label this tube 0.01%. Add to it 900ml of distilled water. Mix gently.

  5. You now have 4 different concentrations of your yeast solutions to grow on a media plate. This will help us to better assess how well the samples grow.  

  6. Obtain media plates for your experiment. Be careful to only remove the lids from the plates when you have to. Each time the lid is removed, contamination can occur.

  7. The Petri plates have a top and a bottom half. For each of your plates, label one end of the lower half of the plate (i.e., the part of the plate with the media in it, the other part is the cover) with an arrow so you know which side is the top (see picture below).

  8. Starting with your 10% yeast tube, place a 5 ml sample of on the left side of your dish. Do not spread the sample around.

  9. Place a 5 ml sample of your 1% solution just to the right of the 10% sample being careful that the two do not touch (see picture below).

  10. Do not spread the sample.

  11. Place a 5ml sample of your 0.1% solution just to the right of the 1% sample being careful that the two do not touch. Do not spread the sample.

  12. Place a 5ml sample of your 0.01% solution just to the right of the 0.1% sample being careful that the two do not touch (see picture below). Do not spread the sample.

  13. If you are adding more than one set of samples to a plate, place the second row of samples below the first (see picture below).

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     Assessing your cultures after they have grown

  1. After 24– 48 hours in the incubator remove your plates.

  2. Examine each of the spots on the plate for size and density. The bigger and more dense the spots are, the better the growth. Conversely, smaller and less dense indicates less the growth.

  3. Sketch, or otherwise record, your data in your lab book. Make sure to label your sketches.