Common baker's yeast, also known scientifically as Saccharomyces cerevisiae, contains 16 chromosomes. This is in its haploid state, a stage of the fungal organism's life cycle in which it reproduces via budding, which is the most usual state for yeast.
Baker's yeast also has a diploid state, meaning it possesses double the number of chromosomes, or 32, in contrast to the haploid state. The diploid state allows yeast to sexually reproduce and form ascospores. However, this double set of chromosomes is created by combining the individual chromosomes of two haploid state yeast cells. The extra chromosomes are simply two sets of 16. Therefore, while baker's yeast sometimes has 32 chromosomes, it only has 16 unique chromosomes, and it usually possesses only these 16 in its nucleus.