Figure 1.

Freeze tolerance of cells harvested from the evolved populations. Molasses‐grown yeast cells from the parental (●), 50‐ (), 100‐ () and 200‐generation (○) evolved populations were transferred to LD medium and total CO₂ production at 30°C was measured before (control, time 0) and after freezing and frozen storage at −20°C for 7, 14 or 21 days. The amount of CO₂ produced for 180 min at 30°C was recorded in a home‐made fermentometer. Frozen samples were thawed at 30°C for 30 min before measuring gassing power. Values are expressed as ml of CO₂ per sample. In all cases, values represent the means of at least three independent experiments. The error associated with the points was calculated by using the formula: , where n is the number of measurements. Additional details are given in the Experimental procedures section.