Yeast reproduce through budding, a form of asexual reproduction. In budding, a small outgrowth, or bud, forms on the parent cell. The nucleus of the parent cell replicates, and one copy of the nucleus migrates into the bud. The bud grows larger and eventually detaches from the parent cell, becoming a new, independent yeast cell.
Fission refers to the splitting of an atom's nucleus, releasing a tremendous amount of energy. This process is not relevant to yeast or any biological organisms.
It's important to distinguish between the biological process of budding in yeast and the nuclear process of fission in atoms.
