A chromosome is a single deoxyribonucleic acid (DNA) molecule with its associated protein components. In the case of many viruses, most bacteria, and eukaryotic organelles, this DNA molecule is circular; but in the case of most eukaryotic organisms with cell nuclei and large genomes, the genome is partitioned between a number of linear DNA molecules. In simple eukaryotes such as Saccharomyces cerevisiae (baker's yeast), the relatively small size of the genome (more than 12 million nucleotide base pairs) has made the analysis of these chromosomes rather easy at the DNA level. Much progress is being made in understanding the proteins involved in chromosomal processes such as DNA replication, recombination, localization within the nucleus, and segregation of the replicated chromosomes to the daughter cells with high accuracy. This last function is arguably the most fundamental role of the chromosome.