FIGURE 19-3 The budding yeast S. cerevisiae. (a) Scanning electron micrograph of S. cerevisiae cells at various stages of the cell cycle. The larger the bud, which emerges at the end of the G₁ phase, the farther along in the cycle the cell is. (b) Main events in the S. cerevisiae cell cycle. Daughter cells are born smaller than parent cells and must grow to a greater extent in G₁ before they are large enough to enter the S phase. START is the point in the cell cycle after which cells are irreversibly committed to undergoing a cell cycle. G₂ is not well defined in budding yeast and is therefore denoted in parentheses. Note that the nuclear envelope does not disassemble during mitosis in S. cerevisiae and other yeasts. The small S. cerevisiae chromosomes do not condense sufficiently to be visible by light microscopy.

[Part (a) SCIMAT/Science Source.]