Yeast artificial chromosomes are genetically engineered chromosomes derived from the DNA of the yeast, Saccharomyces, which is then ligated into a bacterial plasmid. By inserting large fragments of DNA, from 100–1000 kb, the inserted sequences can be cloned and physically mapped using a process called chromosome walking. The primary components of a YAC are the ARS, centromere, and telomeres from Saccharomyces. Additionally, selectable marker genes, such as antibiotic resistance and a visible marker, are utilized to select transformed yeast cells. Without these sequences, the chromosome will not be stable during extracellular replication, and would not be distinguishable from colonies without the vector