What is Human artificial chromosome?

A human artificial chromosome (HAC) is a microchromosome that can act as a new chromosome in a population of human cells. That is, instead of 46 chromosomes, the cell could have 47 with the 47th being very small, roughly 6-10 megabases in size, and able to carry new genes introduced by human researchers. Yeast artificial chromosomes and bacterial artificial chromosomes were invented before human artificial chromosomes, which first appeared in 1997. They are useful in expression studies as gene transfer vectors and are a tool for elucidating human chromosome function. Grown in HT1080 cells, they are mitotically and cytogenetically stable for up to six months.