Vegetative Reproduction : Yeast reproduces vegetatively either by fission or by budding. Depending on this character. They are grouped as fission yeast (Schizosaccharomyces) and budding yeast (Saccharomyces)
1. By fission : During reproduction by fission the parent cell elongates. The nucleus divides into two daughter nuclei and gradually a transverse partition wall is laid down somewhat near the middle, starting from periphery to the centre dividing the mother cell into daughter cells. The two daughter cells so formed, may remain together for sometime and begin to divide again or they may separate soon and then divide.
2. By budding : Budding yeasts are rather common than the fission yeast. At the commencement of budding a small protion of the cell wall, usually near the end, softens. The protoplast of the mother cell covered by a thin membrane bulges out in the form of a bud which ultimately develops into a daughter cell. Meanwhile , the nucleus of the mother cell divides mitotically, (according to some, the division is amitotic). One of the two daughter nuclei migrates into the enlarging bud. The bud grows until it attains the size of the mother cell. The daughter cell then becomes separated from the mother cell and the process may be repeated indefinitely.
Under conditions of rapid growth, the daughter cell also starts producing buds before being detached from the mother cell and the process may be repeated several times, giving rise to chains or groups of yeasts cells. This results in the formation of branched or unbranched pseudomycelium. The cells in chains of pseudomycelium are loosely joined together. Sooner or later, however, the chains break into their constituent cells.